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of moving the heaviest pumps and all electrical equipment should be protected from being flooded sufficient storage should be provided in sumps or otherwise vertical or submersible pumps should be used to take water from sumps in severe conditions the pump room should be protected with an adequate pressure door and a raise for access and ventilation capacity should be added if needed sufficient controls usually at least automatic start andstop alarms for high water and protection for pumps and motors should be provided positive suction head should be provided if reasonably possible by pumping from sump with vertical pumps or locating pump room lower than sump high tension items should be protected from accidental jets and splashes floor should be sloped and a drain provided ventilation should be used as needed for normal and emergency operation discharging hot air to the mine or returning it to the surface or if both are objectionable cooling it mechanically adding to the temperature of water discharged system design the first decision required in the design of a pumping system is whether to pump dirty water or to remove the solids to enable the use of clear water pumps this will depend on a number of factors including the volume of water to be pumped the properties of the water the depth of the workings the expected life of the mine and demands and constraints on disposal and or reuse of the water the second decision is to consider whether to pump in stages or in a single lift from the bottom of the mine some of the considerations include whether the water will be clarified or not before pumping the depth and vertical and lateral extent of the workings the expected life of the mine the type of access available shaft and or decline whether the overall mining sequence is top down or bottom up and whether development of the mine is progressive or largely completed prior to production clearly these two decisions are interdependent and the overall system selection will consider all of these factors some general principles are listed here deep mines with large water volumes and long life will favor clarification and clear water pumping high capital cost but lower operating cost shallow mines with low water volumes and shorter life will favor dirty water pumping a top down mining sequence with progressive mine development will favor a staged pumping system a mine with large vertical and lateral extents will favor staged pumping a shallow mine with limited vertical extent will favor single lift pumping pump selection some of the types of pumps used in underground mining are described in this section small portable or semiportable pumps sump pumps may be powered by compressed air or electricity they are usually vertical centrifugal pumps with open impellers and abrasion resistance or less commonly diaphragm and displacement pumps they are moved to and from sumps where the

y normally work submerged but can run dry without damage and must be self priming compressed air pumps are limited to heads of about 100 m at flows less than 1 l s but can deliver up to 10 l s at low heads electric pumps exceed these limits and can be used to clear small inflows from shaft bottoms clean sumps and so forth where high portability is desirable reciprocating positive displacement pumps these include dirty water pumps mud pumps slurry pumps and grout pumps powered by compressed air or electric motors through belts or gears plunger pumps and diaphragm pumps have high abrasion resistance and low to moderate capacity but are capable of high discharge pressure valves are accessible for cleaning some positive displacement pd pumps displace the fluid directly either via a piston working in a cylinder or a plunger working through a stuffing box a supply of clear high pressure water may be required to lubricate glands and minimize wear a diaphragm pump has a flexible diaphragm between the fluid being pumped and a chamber containing oil that is displaced by a piston thus preventing any wear on the piston side figure 9 6 9 in large sizes pd pumps are used together in main pump stations to deliver 100 l s or more of dirty water directly to the surface from depths exceeding 1 000 m single stage horizontally split centrifugal pumps these are usually directly connected to electric motors for compactness dependability and ease of control discharge sizes are up to about 300 mm generally furnished with close clearances for clear water these pumps can work with high efficiency to capacities of about 200 l s and heads to about 150 m pumps are made for larger capacity at somewhat lower heads installation and maintenance are simpler than for multistage pumps horizontal multistage centrifugal pumps these are usually direct connected to electric motors for compactness dependability and ease of control figure 9 6 10 discharge sizes are from 75 to 250 mm with 2 to 10 stages although total efficiency is likely to be less than that of singlestage units efficiency per stage may be higher heads typically range from about 150 to 700 m although the first cost of these pumps generally is higher than for single stage pumps of similar power their use may save the capital and operating costs of duplicate facilities the close tolerances require clean water to prevent excessive wear so the cost of building and maintaining settling dams is a consideration vertical turbine deep well pumps these are essentially vertical centrifugal pumps made in comparatively small diameters to work in water wells and similar narrow but high spaces water ends are essentially similar whether close coupled to a vertical electric motor connected by a long shaft to a motor at the top of a well casing or connected to a submerged motor in the well vertical turbines are made with as many as 20 or more bowls stages for heads of 5 to 30 m per stag

e pumps are made in diameters from about 150 to 1 000 mm or more because pump intakes normally are submerged priming is not a problem motors of close coupled pumps can be well above normal water levels impellers can be removed if a pump is to work at less head or more bowls and impellers can be added for greater head vertical centrifugal pumps these are made in one and two stages with proportions like those of horizontal centrifugals they are direct connected below vertical motors by short shafts because the pump always works submerged priming is not a problem they have the simplicity and high capacity of horizontal centrifugals and in many applications approach or equal the convenience of vertical turbines although total efficiency is likely to be less than that of singlestage units efficiency per stage may be higher heads typically range from about 150 to 700 m although the first cost of these pumps generally is higher than for single stage pumps of similar power their use may save the capital and operating costs of duplicate facilities the close tolerances require clean water to prevent excessive wear so the cost of building and maintaining settling dams is a consideration vertical turbine deep well pumps these are essentially vertical centrifugal pumps made in comparatively small diameters to work in water wells and similar narrow but high spaces water ends are essentially similar whether close coupled to a vertical electric motor connected by a long shaft to a motor at the top of a well casing or connected to a submerged motor in the well vertical turbines are made with as many as 20 or more bowls stages for heads of 5 to 30 m per stage pumps are made in diameters from about 150 to 1 000 mm or more because pump intakes normally are submerged priming is not a problem motors of close coupled pumps can be well above normal water levels impellers can be removed if a pump is to work at less head or more bowls and impellers can be added for greater head vertical centrifugal pumps these are made in one and two stages with proportions like those of horizontal centrifugals they are direct connected below vertical motors by short shafts because the pump always works submerged priming is not a problem they have the simplicity and high capacity of horizontal centrifugals and in many applications approach or equal the convenience of vertical turbines vertical centrifugal pumps are made for capacities up to 950 l s and heads to 250 m with motors as large as 1 000 kw they are commonly used to raise water from a lower to an upper sump from which it can flow with positive suction head to horizontal centrifugals they also can pump to emergency storage air lifts the efficiency of an air lift is low at best yet there is no simpler pumping system typically two strings of concentric pipe are submerged and compressed air is introduced through the internal pipe anything that can get into and through the larger pipe is

pumped without doing damage they are especially good in dewatering partially blocked shafts but require a minimum submergence of around 33 and so cannot completely dewater a shaft progressive cavity pumps with abrasion resistant rotors in rubber stators progressive cavity pumps will pump any mud that can be drawn into them they are widely used in mine dewatering figure 9 6 11 multistage units are capable of heads up to 720 m at up to 60 l s or flows up to 150 l s at lower heads testing performance of pumps well equipped manufacturers have extensive facilities for testing large pumps with precision comparable test facilities are uncommon in deep mines yet records of performance are essential to evaluate the results of pumping and to guide maintenance modern pump stations are often well instrumented but serviceable data can be obtained by such means as the following the total output by a weir on the surface can be measured integrated and recorded in some cases it is possible to measure rate by pumping into or out of a large sump or tank but usually with less accuracy inflow can be estimated by adding the water removed with ventilating air and subtracting any water piped into the mine for drilling and washing and decant water from hydraulic fill the pumping rate of each pump can be measured by any of several means including magnetic flowmeters venturis orifices weirs or pumping from or into a sump provision of these measuring devices in the discharge of each pump makes it possible to check each periodically with little labor and loss of pumping time individual discharge and suction heads can be measured with calibrated bourdon type gauges or manometers placed appropriately mechanical input can be determined from a calibrated watt hour meter subtracting the motor loss as taken from the manufacturer s test data various torque dynamometers can be used for a more fundamental determination of power input pump speed can be measured by a calibrated tachometer and stopwatch and this is generally adequate the rate of discharge of a centrifugal pump and its discharge pressure can decrease with time because of scale formed in the discharge or other change increasing the dynamic head decrease in suction head due to scale obstruction of intakes and so forth decrease in effective diameter of the impeller or other severe pump wear blocking or other obstruction of the impeller passages and wear causing excessive leakage between stages of multistage pumps and across wear rings in single stage all pumps discharging into a single line should be kept balanced to operate together efficiently if unbalanced the head of one pump could decrease until flow is reduced to the degree that the pump bearings seize cost of pumps usually other factors are likely to be more significant than the first cost of the pump the cost of standard water ends of horizontal centrifugal mine pumps generally is 30 to 50 of the total cost o

f the pump motor starter unit it may be only 5 to 15 of the cost of the pumping plant including sumps clarification power supply ventilation suction discharge and required excavations the construction of the pump influences the cost of the station e g vertical pumps require less floor space and no suction line efficiency is important because power ordinarily is the largest part of operating cost where planning makes it practicable a single high head pumping installation can be more efficient as well as simpler than a series of pumping stations each working at a lower head initial duty calculations can be made assuming efficiency of 60 motor pump for small units 75 for larger pumps and up to 80 for units of large capacity large units in which both motor and pump are excellently matched to the pumping duty may go higher e g 90 pump 93 motor pipework normal working pressures may be increased considerably by the pulsations of reciprocating pumps or by surging and water hammer special steels or extra wall thickness may compensate for pressure or corrosion but with added cost or weight where significant ground movement is likely the discharge pipe should be able to survive some misalignment if it is likely that individual lengths or sections of a discharge line must be removed to clean scale or repair accidental damage pipe should be coupled and supported accordingly in some places repair by cutting and welding is difficult in some cases reasons exist for not treating water underground and protection of the outside of the steel pipe is likely to be incomplete the angle of the pipe its exposure to accidental damage working room and service facilities also are factors in selection of pipe and couplings and how it is supported because many of these factors are difficult to evaluate continuous dependable service is important and repair can be highly inconvenient innovation in high pressure design pipe is uncommon preference for seamless steel pipe for high pressure lines has decreased with better quality control in welding highpressure lines usually are no larger than 250 mm 10 in to limit the weight of long steep columns facilitate placement and repair in limited shaft compartments reduce the number of pumps discharging to the same line and make it easier to provide a spare line wall thickness needed for any pressure is calculated from the minimum ultimate tensile stress with a good factor of safety 5 is frequently used in shaft rising mains whereas 2 may be acceptable in more accessible areas there is much more latitude in choice of pipe for lower pressures such as discharge from single stage pumps where volumes are large 500 mm 20 in pipe may be used on high pressure lines the practice is to join pipe with flanges simple flanges generally are preferred but gasket material must resist extrusion by strength or by retention these long strings generally are assembled from th

e bottom up by adding one or several lengths with the use of a cage with extensible crawls to handle the pipe and decks where crews work more than 100 m of pipe can be placed in a shift weight usually is carried on steel bearer beams or brackets concreted into the shaft wall at intervals of 120 m or less the provision of an expansion joint below each bearer assists in equalizing weight adds vertical flexibility and makes it unnecessary to raise an entire string to replace a length continuous rising mains can be added in 20 m lengths with each joint welded as it is added at the surface like well casing alternatively screwed well casing may be used guides prevent side movement but all weight bears either on a concrete bridge at the elevation of the pumps with the line in compression or is suspended from a bridge at the surface with the line in tension gate and check valves are placed in the discharge of each centrifugal pump for use in starting and for protection during the repair of a pump connected to an active discharge line bulkheads and plugs deep gold mines in south africa have developed outstanding practice with plugs demonstrated in tests and in both routine and emergency construction generally these plugs were built in hard strong quartzite impermeable except on fractures culmination of this development came with the four plugs placed in emergency conditions in the west driefontein mine in november 1968 at depths below 1 000 m they were completed 20 days after the inrush in 3 0 3 7 m crosscuts work was undertaken with water flowing more than 1 m deep on each level valves to stop bypassing water were closed on the 23rd day and the lower plug withstood a head of 1 116 m of water on the 26th day cousens and garrett 1969 several conclusions are reached from south african practice garrett and campbell pitt 1961 generally it is more difficult to stop leakage past a bulkhead than to make it strong enough to resist thrust passage of water through rock fractures is related to the pressure gradient which should be moderate many plugs are neither hitched tapered nor reinforced reliance is placed in the strength of the concrete bearing against the usual irregularities of the rock surface such plugs have withstood pressures of more than 6 9 mpa one at 15 5 mpa no indication of structural failure resulting from thrust was noted in the examples reported leakage is likely along the floor and roof even at low pressure where mud and honeycomb laitance a weak layer due to excess water and air pockets commonly weaken the rock concrete contact these leakages sometimes are sealed acceptably by one stage of grouting at higher pressures water is likely to break through rock fractures this appears to result from rock movement induced by pressure on rock surfaces part of the water entering the fractures may not appear outside the bulkhead much of this leakage can be sealed by several stages of cement grouting

at pressures to at least 2 5 the hydrostatic head in holes drilled as far as 10 m into the rock the effect of each stage of grouting seems to be to fill the fractures perhaps poststressing the ground around the bulkhead and increasing its resistance to the entrance of water the loss of several bulkheads subjected to more than 6 9 mpa is attributed to failure of gaskets threaded plugs and other fittings the possibility that even the smallest leakage through fractures may be enlarged by high pressure erosion should not be underestimated preferred construction is by injecting cement sand grout into clean strong angular rock previously packed between timber forms this generally results in better concrete easier logistics and in some circumstances less time and cost than direct concrete placement ordinary portland cement usually is used but rapid set cement can be required by urgency concrete should reach at least 17 2 mpa in 28 days the four plugs at west driefontein were made of cement sand slurry only slurry can be mixed under good control at a central plant and pumped more than 1 000 m through small pipe horizontal cold joints should be avoided by all means recommendations from this work include seeking sites in tight sound rock in good ground at least keyways are unnecessary but note the length next recommended the plug should be long enough that the pressure gradient is moderate in one test a gradient of 9 mpa m was reached after several stages of rock grouting but for working bulkheads designed gradients of 900 to 1 400 kpa m have proved effective i e for each 6 9 mpa allow between 8 and 12 m of plug all mud and loose rock should be removed the water flow across the floor should be stopped and a ventilation hole provided for high spots in the roof pipe gaskets valves and fittings should be tested at a pressure somewhat greater than that to be withstood several stages of grouting to reduce leaks should be planned the first through pipes at concrete rock contacts might be at around 2 000 kpa but later stages through holes drilled successively deeper into the rock can be at successively higher pressures up to at least 2 5 the expected hydrostatic head comparable experience in other rock is unknown but several inferences seem to deserve consideration in any strong rock that can be grouted effectively similar practice seems applicable in weaker rock however or one with seams that do not take grout well it appears prudent to work to lower pressures and lower pressure gradients to reduce the risk of uncontrollable leakage through erosion and enlargement of rock permeability or defects no large excavation should be subjected to pressure greater than the maximum hydrostatic head unless after full study and evaluation of rock stresses lastly the use of expanding cement using aluminum powder or similar seems promising inrushes an inrush is a low probability but high impact event usually le

ading to major disruptions to production and multiple fatalities for example vutukuri and singh 1993 tabulate 33 mine inundations in england scotland india and the united states having an average of 31 and a maximum of 375 fatalities at chasnala colliery jharia india in 1975 one definition of an inrush is the uncontrolled mass movement of material whereas subsidence is a sudden collapse of a large volume of rock often referred to as plug or pipe subsidence mccarthy and harvey 1998 these definitions recognize that flows of mud tailings wet ore or saturated surface material may also become inrushes and that sudden subsidence although a hazard in itself can create unexpected connections to these materials causes of inrushes a review of 43 examples of inrushes mainly in noncoal mines shows the following causes mccarthy and harvey 1998 a further 18 examples gave insufficient details for classification surface flooding enters mine 33 mining broke into old workings 28 strata water enters mine 19 accidental connection made with sea river lake etc 14 failure of a dam seal borehole etc 5 earthquake 1 it is interesting to compare this list with the next which was prepared by job 1987a 1987b based on 208 incidents in british collieries during the period 1851 to 1970 the much greater frequency of contact with abandoned workings is to be expected in intensively exploited bedded deposits the lack of surface flooding may reflect a greater predictability and awareness of flood levels than has been the case in arid environments this list does not include fill bulkhead failures which are common but rarely become public knowledge unless a fatality is involved contact with abandoned old workings 78 clearing old shafts or shaft sinking 9 failure of an underground dam or seal or leakage of a borehole 4 contact with surface water pond river canal or stream 4 contact with surface unconsolidated deposits glacial or organic 4 strata water entering working 1 frequency and location of inrushes a survey of mining periodicals for the years 1980 1996 identified 33 inrush incidents involving fatalities or loss of production this is a rate of about two incidents per year worldwide not including unreported incidents in china and the former ussr these locations are for inrushes from 1980 to 1996 africa 9 north america 6 southeast asia 5 australasia 5 europe 5 india 2 south america 1 the occurrence of inrushes seems to generally correlate with the level of underground mining activity without new preventive measures a country such as australia should experience one incident every 3 4 years as about 70 significant underground mines exist in australia the return period for an inrush incident is 238 years which means that personal experience and awareness of the hazard are likely to be low the nature of low probability high impact events means that a seve

re incident could happen at any time and that special management procedures are required to maintain awareness more recent instances particularly in coal mines in north america and china suggest that this problem remains a significant one is a serious threat to employee safety and has a serious impact on the public perception of the mining industry surface water disposal all of the water and associated sediments removed from the mine must be disposed on the surface or recycled some water is disposed into the atmosphere via the exhaust ventilation and evaporation from wet rock dumps and water storages in many mines the water from underground is an important source for processing operations and other surface operations today even if the mine water is of better quality than the water in local streams direct discharge into surface waterways is often not permitted or requires extensive and expensive purification the presence of heavy metals or acidity will exacerbate this situation mines with superfluous water may construct evaporation ponds for water disposal this is not particularly effective in cold climates with low evaporation rates in some cases properly treated mine water can be an important water source for the surrounding community any water discharged into the natural environment should meet internationally accepted water quality standards what is physical asset management a mining organization is critically dependent on mineral resources and a wide range of physical equipment infrastructure and operating systems the economic performance of the enterprise is closely linked to the correct investments extraction strategy system design and selection appropriate use high performance reliability safety and maintenance of such physical assets the optimal management of these assets is therefore at the heart of good mining business management the term asset management however has been applied to a variety of asset types and activities over the years so it is important to recognize and distinguish between the current usages of the term to focus on appropriate business priorities and value the financial services sector for example has long used the phrase to describe the management of a stock or investment portfolio trying to find the best mix of capital security or growth and interest rates or yield this vision of asset management has close parallels to the physical systems version insofar as it involves juggling investments risks performance and sustainability however there are big differences between financial assets and physical ones and between the options for their management some engineering and industrial maintenance departments and certain software vendors have relabeled their functions as asset management to boost their professional standing and credibility in the organization this however is a restrictive and ultimately ineffective view that misses many of the biggest opportunities asset c

are maintenance is just one part of asset management some of the biggest prizes in effective asset management for example involve optimizing the relationship between asset utilization sweating the assets and the needs for maintenance or renewal this is only possible if a cross functional view is taken of whole life asset management a more holistic view of assets and their management has emerged since about 1990 and this concept of asset management is the focus of this chapter such a model encompasses all aspects of investing in the right assets in the first place exploiting them appropriately caring for them maintenance and ultimately replacing or disposing of them various levels of granularity exist in this context depending on the definition of the asset some organizations limit the term to the management of physical equipment items or process units while others take a more holistic view and define their assets at the level of the whole ore body site or mining enterprise in all such cases however the challenges of optimizing investment operations utilization maintenance and whole life value are similar and are addressed in a publicly available specification pas 55 2008 this standard defines terms and requirements for optimal management of physical assets pas 55 defines asset management as systematic and coordinated activities and practices through which an organization optimally and sustainably manages its assets and asset systems their associated performance risks and expenditures over their life cycles for the purpose of achieving its organizational strategic plan other wordings and definitions are in use in various industries but the most robust ones all include the key elements of this pas 55 definition they identify the coordination and systematic approach the need for optimization and the combined consideration of expenditures asset performance and risk exposures they recognize the need for a whole lifecycle or sustainability view i e the long term and for asset management to be directed toward a clear corporate goal for many organizations such aspirations represent a significant challenge yet the prize for getting it right is substantial benefits of optimized whole life cycle asset management many organizations are tackling the integration and optimization challenges of asset management in all sorts of industries and business environments and they are coming to remarkably consistent conclusions a cross disciplinary whole lifecycle view of asset management yields significant tangible and sustainable benefits compared to the silo behaviors of individual functional departments that have often historically been focused on conflicting and or short term goals typical quoted benefits include thirty percent reduction in total cost of ownership nuon electricity network the netherlands thirty percent reduction in mining equipment maintenance costs with 3 10 increased system a

vailability copper mining chile seventeen percent increased output at 50 lower operating cost shell north sea oil platforms twenty eight percent reduction in planned system downtime u k national grid budget savings of a 11 million per year new south wales government and twenty nine percent increased output at no extra cost baltimore maryland united states power generation further and maybe even greater long term benefits are found through improved credibility in the eyes of customers enterprise investors and other stakeholders good asset management also results in much greater engagement and remotivation of the work force and in more sustainable continual improvement business processes it is not easy however to create such an integrated system in the first place or to resolve the inevitable trade offs that exist between short term and long term effects or among costs performance and risks it usually involves a fundamental review of stakeholder expectations and business drivers and a quantified or consistently scaled method for determining the criticality and value of assets and activities sophisticated tools and processes are also usually needed to optimize the mix of capital investment operating costs performance maintenance requirements risks and achievable economic life spans and education communication motivation and behavioral changes have consistently proven to be absolutely critical success factors modern optimized asset management therefore involves an integrated business model that bridges departmental contributions to deliver net value for money on both short and long time frames in line with explicit business goals what are the assets one of the key messages of pas 55 is that joined up asset management needs to occur at multiple levels in every organization the characteristics and criticality of different assets and asset types vary and the options for investment exploitation care maintenance and ultimate disposal or renewal differ but the requirement to deliver sustainable total value for money remains a consistent underlying objective the pas 55 standard for asset management illustrates this stratified view of assets and their management see figure 9 7 1 in a typical mining enterprise therefore a hierarchy of assets would correspond to the following categories whole mining enterprise including all business functions and locations specific ore bodies and or geographical regions of the enterprise specific mine and associated extraction processing facilities the different extraction and or processing systems discrete equipment items at the corporate or enterprise level asset management simply means good business management however at lower levels asset specific characteristics and divisions of responsibility departments and functions make it increasingly difficult to see the whole picture and optimize the whole life cycle costs and value this is the

area in which a robust asset management strategy helps to ensure coherence between the organization s goals and the day to day realities of who does what when where and why emerging standards in asset management since 1990 two very different business environments have made very similar discoveries about what is needed and what is achievable through a more integrated approach to whole life cycle asset management the north sea oil and gas sector faced massive wake up calls in the late 1980s the piper alpha disaster an oil price crash the cullen report 1990 recommendations on risk safety management market globalization and so on these forced a fundamental reappraisal of underlying business models and the recognition that big companies while holding several strategic advantages and economies of scale were losing the joined up thinking and operational efficiency or agility that smaller organizations naturally enjoy and need in order to survive bp and shell experimented with the creation of a small business culture within a large organization with its attendant leverage asset centered production units emerged employing multidisciplinary teams with significant budget and performance freedoms to find the best combination of investments exploitation and care for each reservoir or production platform the results were spectacular reducing total costs of ownership and raising productivity nearly tenfold while simultaneously raising safety and environmental performance recent high profile events in bp s u s operations texas city refinery and the gulf of mexico leak have of course implied otherwise but the underlying trend has been profound and significant fatalities injuries and environmental incidents have fallen dramatically since the 1980s at the same time public utilities and municipalities in australia and new zealand facing a sustained period of degrading services and escalating costs combined with some highly publicized system failures realized that a different approach to sustainability and value for money was needed the whole asset life cycle needed to be considered and capital investment planning began to take on a cross functional view to find the best value for money options again the results have been spectacular with significant and sustained service improvements cost reductions and reestablished public confidence now the lessons are being adapted and applied to mining road and rail transport water electric and gas utilities process and manufacturing health education and other industries in both private and public sectors there is increasing recognition therefore that many of the good practices in managing assets are generic and there are many opportunities for learning and improving by exploring how other industries are addressing similar problems in different environments in 2002 the institute of asset management iam initiated a project with the british standards institution to doc

ument these observations in the form of a publicly available specification pas 55 was first published in 2004 with the backing of about 25 organizations in the next 4 years it became a mandated requirement for the regulated u k electric and gas utility sectors and was picked up internationally in railways mining water and manufacturing industries the most recent update of the standard published in 2008 pas 55 2008 involved more than 50 organizations from 15 different industries in 10 countries it is currently going forward to form the basis of a full international organization for standardization iso standard with the support of the national standards organizations of more than 20 countries it is safe to say that asset management has thus evolved to become mainstream an expected competency in any organization that is heavily dependent on physical assets resources or infrastructure the understanding of what this involves however is still evolving best practices or even what should be regarded as good practices are constantly moving forward this is why a management system is necessary to coordinate the many functional contributions of an organization with a common understanding and clear purpose optimally managing the inevitable and inherently conflicting subgoals and doing this sustainably while still retaining enough flexibility to cope with future unknowns basic terminology before delving into the specifics of what needs to be done why and how it is necessary to be very clear on terminology a common problem in this field is one of poor communication or misunderstanding of meanings some terms in asset management are used and interpreted very differently depending on role or context while others are simply misused or confusing pas 55 tries to address this with a definitive glossary of 35 common terms the most important of which are reproduced here other useful guidance is to be found in complementary standards such as iso 15663 2000 for whole life costing bs 3811 1993 for maintenance and reliability language and iso 31000 2009 for risk management asset at the simplest level an asset is anything of value tangible or intangible that is owned by the organization in this context however it refers particularly to plant machinery property natural resources buildings vehicles and other physical items or infrastructure however the principles and practices of good asset management also apply to other asset types data or information reputation financial resources licenses or entitlements natural resources etc note also the relationships between individual assets within functional asset systems and portfolios of assets see figure 9 7 1 asset life cycle an asset life cycle is the time interval that commences with the identification of the need for an asset and terminates with the decommissioning of the asset or any associated liabilities the principal stages of an asset s life cycle typical

ly include creation acquisition use maintenance and renewal disposal asset management asset management comprises the systematic and coordinated activities and practices through which an organization optimally and sustainably manages its assets and asset systems their associated performance risks and expenditures over their life cycles for the purpose of achieving its organizational strategic plan asset management system the asset management system comprises the organization s asset management policy strategy objectives and plans and the activities processes and organizational structures necessary for their development implementation and continual improvement a management system also includes the organizational structure roles and responsibilities planning activities standards information systems practices processes procedures and resources asset management information system the information system usually computerized is for the storage processing and transmission of asset management information such as asset registers drawings contracts licenses legal regulatory and statutory documents policies standards guidance notes technical instructions procedures operating criteria work plans asset performance and condition data or audit results such systemsare sometimes referred to as enterprise asset management systems their role however is largely that of a computerized maintenance management system and they should not be confused with the larger scope of the life cycle business management of physical assets an asset management system as described in this chapter asset management policy the asset management policy is a specific mandate that states the principles commitments obligations and control framework for the development and implementation of the asset management strategy and plans it must be clearly derived from the organization s corporate values and strategic plan and must be complementary to not conflicting with other company policies such as those for safety health and environmental commitments asset management strategy the asset management strategy is a vital centralized and cross disciplinary view of the long term optimized approach to the management of the assets it needs to reflect the top down requirements and goals of the business and the bottom up realities of the assets including their condition performance capabilities and opportunities it also needs to provide enough coordinated clarity and detail that specific asset management plans who will do what when where and why can be derived and optimized asset management objectives two levels of asset management objectives should be considered asset management objectives need to be defined for specific and measurable outcomes or achievements required of the physical assets and asset systems e g how assets themselves need to perform and specific and measurable outcomes or achievements requi

red of the overall asset management system e g how asset management should perform this reflects the need for a scheme of asset management performance monitoring in the context of other corporate business priorities asset management plan an asset management plan is a document that specifies activities resources responsibilities and time scales for implementing the asset management strategy and delivering the asset management objectives such a plan needs to be optimized for cost risk performance and sustainability in line with the planning horizons for the asset life cycles and the company business plan optimization this is the process required to achieve the best value compromise between conflicting factors e g performance costs and risks within any nonnegotiable constraints optimization requirements exist in many areas of asset management such as trade offs between short term and long term goals or between capital investment and operating costs or between costs and risks the processes of optimization are explained and illustrated later in this chapter structure of an asset management system an integrated system for managing assets is primarily a coordination mechanism for breaking down the silos of individual departmental roles and activities in favor of delivering the mining enterprise s core objectives like any other management system however it is a set of connected processes controls and enablers that ensure the right things are done for the right reasons in the right way to deliver the objectives and enable ongoing flexibility and continual improvement care should be taken not to confuse an asset management system with either of these systems asset system the functions of the physical equipment and infrastructure in production systems asset information management system asset registers work planning and history collection systems an asset management system is not a software tool nor is it the hardware comprising the production or processing plant and infrastructure itself the management system for assets rather is in the same category as a quality management system a safety management system or an environmental management system it includes statements of policy some clear strategies objectives and plans and a range of delivery mechanisms along with performance monitoring review and improvement processes an asset management system is particularly focused on the coordination and integration of what takes place to break down the barriers between departmental contributions and their localized self interests or short term goals this requirement emphasizes the optimization of the combined effects and value for money resulting from investments asset usage and asset care over the whole life cycle it also highlights the importance of clarity communication and alignment between asset management activities and the overall purpose of the organization the need to understand where th

e organization is going and why before determination is made of what is therefore worth doing when and how for example a mining enterprise may have the goal of maximizing the total lifetime yield and margin from an ore body so the development use and maintenance of facilities developed to support extraction should be planned with this horizon and total value in mind not just year by year budgeting or the selection of cheapest equipment options or at the other extreme the gold plating of technical solutions when the incremental expenditures are not worthwhile figure 9 7 2 is a high level view of the most important attributes of a joined up management system for physical assets the boundary of such a system can be seen as sitting just beneath the organizational strategic plan the company s overall business plan this is the interface at which the language of business drivers and stakeholder expectations e g safety profit reputation quality must be translated into the practical and specific implications or requirements for creation use care and renewal disposal of the physical assets or systems required to deliver these objectives within an asset management system that is compliant with pas 55 it is necessary to develop and demonstrate a logical and transparent top down chain of connectivity from the overall business objectives to a clear definition of policy mandated obligations and principles and from preferred or optimal strategies and objectives to the specifics of what needs to be done to which assets why when and how i e asset management plans this sounds obviously desirable and logical but it often proves very hard in practice the language used in corporate initiatives and priorities is often very different from day to day operational language priorities and expectations change and short term objectives conflict with long term goals a very important bottom up influence must also be established and exploited the asset portfolio s diverse characteristics needs risks and opportunities shouldbe influencing the organization s strategies and even its strategic plan later in this chapter the practical steps needed to establish and maintain such alignment are discussed of course asset systems and assets are diverse in type role importance capability performance and health so whatever the overall strategy there is a vital optimization to be done in determining what is the best mix of investment exploitation maintenance and renewals to deliver the most value for money optimization is a much overused and misused word but it is correctly applied here the requirement is to find the best blend of competing factors such as cost versus performance versus risk or capital cost versus operating costs or short term versus long term results such optimization and decision making is at the core of good asset management and there are many significant developments in this area these are also summarized

later in this chapter the right side of figure 9 7 2 addresses the need for continual improvement using the reality of assets and operating maintenance experience to modify plans strategies the whole organization s ambitions and even the expectations of the stakeholders in addition the underlying enablers or lubricants of the whole management system must not be forgotten these profoundly influence the combined performance and sustainable nature of the asset management system ever since the industrial revolution businesses have increasingly specialized their activities and job functions in the search for greater efficiencies and performance one result is the increasing difficulty for any individual or functional department to see the whole picture and understand the effects of doing something for apparently good local reasons e g saving 5 in the purchasing costs for a major project that has unanticipated performance cost or risk consequences on other parts of the business e g performance maintenance or spares impact to minimize these false economies and ensure that net value for money overrides any local vested or departmental interests an asset management system must include a range of important enablers such as good communications clear roles and responsibilities competencies risk management and so on these are discussed in detail later in this chapter asset management processes business processes that are more specific can be identified in the life cycle management of physical assets these correspond to many of the daily functional activities in any mining enterprise however their integration coordination and optimization represent the greatest challenge and opportunity for improved efficiency and effectiveness figure 9 7 3 shows a simplified view of these main functions seven key features of a good asset management system to precede an expanded discussion of the components and functions of an effective asset management system it is necessary to recognize some underlying generic requirements these are characteristics of the whole system and provide an important frame of thinking within which the component activities methods tools responsibilities and performance measures should be considered as part of the development of pas 55 the participating organizations identified seven key features that characterize good and effective asset management systems see figure 9 7 4 1 holistic cross disciplinary and focused on the total picture and total value 2 systematic rigorously applied in a structured management system 3 systemic looking at assets in their own systems context seeking net total value for money rather than component or localized goals 4 risk based incorporating risk consciously and appropriately into all decision making and planning 5 optimal seeking the best net compromise between conflicting objectives such as costs versus performance versus risks or short term versus

long term benefits 6 sustainable delivering optimal whole asset life cycles rather than artificial short term results at the expense of long term consequences the management system itself also needs to be agile and sustainable in the face of future uncertainties and inevitable change 7 integrated the importance of being joined up and collaborative this is at the heart of good asset management the total jigsaw puzzle needs to work to be more than the sum of its parts these generic principles apply to all asset management activities they should be evident features of investment planning resourcing contract management organization structures materials management work scheduling information capture and use and a host of other business functions they form a central feature of a maturity scale for asset management and are good indicators of the likely performance robustness flexibility and sustainability of the company s core functions if it is heavily dependent on physical assets the iam has for example developed a five level maturity scale against all the pas 55 requirements that is widely used for gap analysis benchmarking improvement planning and so on iam 2002 the need to improve the productivity safety and profitability of mining is driving the widespread application of automation technologies in mines automation in its many forms is something that miners interact with on a daily basis but may be unaware of its existence the current implementation of mining automation and robotics has not yet significantly changed mining processes it has however begun to demonstrate its potential value to improve the productivity and safety of these mining processes and associated unit operations this has lead to a growing vision within the industry that fully automated robotic mining will be a major part of mining in the near future this vision includes mines that have the following capabilities automated personnel and equipment tracking automated materials handling trucks loaders conveyors sizers smart drills automated drilling of holes and recognition of material characteristics accurate and automated movement and positioning of all mining equipment automated mechanical mining systems remote supervision from distant locations intelligent and integrated control over all mining processes to optimize resource value benefits of mining automation why does this vision of a fully autonomous mine exist today traditionally the main perceived benefits for introducing mining automation have been improved safety removing operators from hazardous and stressful mining environments higher productivity through the improved performance of individual machines more metric tons per hour and reduced downtime automated machines see less duty than human operated machines and reduced labor costs automation removes operators from machines penman 2002 suggests labor accounts for approximately 20 of the cost

of operating a large haul truck although these benefits are still appropriate today the current renewed interest in automation and robotics in mining is related to the following perceived additional benefits limiting operational variance automation allows machines to be controlled so that their output is well defined for example an automated shovel would load more consistent bucket payloads this allows a truck size to be selected for the shovel that will be consistently loaded to its target payload improved precision automation means mining tasks are executed at their planned locations and times for example an automated blasthole drill will drill blastholes at their precise location and specified depth as designated by the blast pattern holmes 2006 this means the outcomes of blasts are more consistent and generate the desired rock fragmentation which has significant downstream benefits the more significant benefit of limiting operational variance and improved precision is that they enable production consistency this means that mine designs and more specifically mine plans as well as production and schedules can be generated where there is a valid expectation that they can be achieved automation allows mining processes to be controlled more effectively more like manufacturing facilities where individual processes as well as the complete mining process can be optimized the introduction of automation is expected to serve as a catalyst for new credos for mining similar to those that have evolved through introduction of total quality management methodologies to manufacturing definitions to understand what mining automation and robotics are and what potential impact they have on mining operations it is important to define the basic terms mechanized operations performed by machines automatic does not make decisions but completes task by following well defined rules semiautomatic partly automatic and partly manually controlled automation mining tasks completed by machines without human workers autonomous functions independently without human supervision robotics machines with high level capabilities to sense and reason about their environment such machines are required for successful automation of tasks in high variable and unpredictable mining environments intelligent machines with the ability to learn understand and deal with new situations what makes mining automation challenging automation is used extensively in many other industries and has demonstrated great value in improving productivity gaimon 1985 carlsson 1995 its successful use in the manufacturing sector is in the automation of well defined manufacturing cycles of identical components in a well known and well structured environment mining is typically conducted as a series of discrete steps or unit operations by groups of equipment types working in tandem such as drilling blasting loading hauling ground control and materia

ls processing here the highly variable and unpredictable mining environment affects the successful execution of each or sequences of unit operations thus automated mining systems must be able to sense reason and adapt to this unpredictable environment in order to function effectively in addition these systems need to operate for 365 days per year in very harsh mining environments for these reasons many existing automation technologies from other industries are not readily transferred into mining the growth of robotics driven primarily by the military has provided the tools necessary to develop autonomous mining systems these developments have been driven by low cost increases in computing power new algorithms for signal processing perception and control and in particular new sensing technologies such as global positioning systems gpss and radar and laser systems durrant whyte 2009 these tools are essential to accurately locate control and coordinate the activities of robotic machines onboard sensors can generate real time maps of the mine environment geometry and geology around these machines so they can be optimally controlled this spatial control information is essential to plan and schedule the complete mining process including machines this will make mining operations more precise and predictable like a factory and ultimately dramatically more productive fully autonomous mining that encompasses the complete spectrum of mining processes will be expensive and require significant technical development more importantly it will only be achieved through significant change management of mining culture to accept these innovations mine automation technologies will achieve the highest probability of success using a multistep implementation program the resulting early introduction of technologies can provide mining benefits such as operator aids that improve machine performance and reduce machine damage improved mine sensing systems that can provide managers with better information about the state of the mine new mine models that allow managers to execute operational decisions semiautonomous and remote control capabilities that remove operators to safer environments and collision avoidance technologies that prevent accidents mining robotics the science field robotics is now well established in the research commercial and military arenas mining robotics is a stream or application within field robotics the basic science with associate sensors computing hardware etc that drives the technology in this field is not being developed by the mining industry however mining robotics is using and reengineering this technology several good textbooks and journals explore the extensive science and technology of field robotics buehler et al 2010 siegwart and nourbakhsh 2004 everett 1995 and ge 2006 are excellent references for more detailed information evidence of the close link between res

earchers in field robotics and mining equipment manufacturers is caterpillar s sponsorship of the carnegie mellon university cmu participation in the defense advanced research projects agency darpa grand challenge competition this competition tests the performance of autonomous ground vehicles in a series of different outdoor environments and demonstrates the state of the art in mobile robotics cmu won the last competition in 2007 and has been in a longstanding partnership with caterpillar to develop automated mining equipment binning 2009 a very large body of basic research into the development of autonomous vehicles includes major themes such as route planning al hasan and vachtsevanos 2002 frazzoli et al 2002 salichs and moreno 2000 obstacle detection and avoidance azouaoui and chohra 2002 close maneuvering strategies gomez bravo et al 2001 and autonomous vehicle control system design pereira 2001 mining automation and robotics in practice this section provides an overview of selected automation solutions for the mining industry some are commercially available others are being trialed at mine sites as precommercial technologies and some are still in the research and development r d stage detailed published information about many of these systems is difficult to find as manufacturers and mines are reluctant to release information that might hurt their competitive advantage autonomous haulage systems technology autonomous haulage systems are generally divided into two major divisions site level systems sometimes called the office site manager and machine level systems sometimes called the onboard controls site level automation the site level systems provide an interface between the human and software based mine planners provide data for business tracking and provide optimization and control over the haulage system machines mine planning is defined as determining the goals and priorities and communicating them to the mine management tools and mine management is defined as optimization of existing resources to accomplish the goals mine planning this requires significant human interaction to set goals such as prioritizing production volume versus cost factors fuel usage risk of machine damage or prioritizing short term production versus long term mine efficiency the challenge in mine planning is to ensure that both explicit and implicit goals are accurately translated to the more automated mine management system mine management fortunately there is a large body of experience with mine management systems however a new generation of mine management systems will be required to address the requirements of autonomous systems the next generation of such systems will require much more detailed mine models and many new features to manage autonomous equipment machine level automation machine level automation requires the ability to understand what tasks need to be accomplished highlevel planning

determine location positioning perceive the environment based on the location perception based on the environment and position plan future tasks to achieve the desired goals task level planning execute the planned primitives primitive execution and handle exceptions high level planning high level planning is the ability to interpret directions from the mine management system and to select the appropriate behaviors for example if an autonomous truck is directed to a load area it needs to understand the path validate the path and ensure that it has the required behaviors and capability to execute the plan positioning positioning is the ability to determine the machine s pose meaning its location and orientation for autonomous machines an accurate reliable pose is critical although absolute accuracy is actually not as critical the ability to accurately register the machine s pose to the mine model is a requirement multiple types of positioning must be considered for aboveground applications the most common realtime kinetic global navigation satellite systems rtk gnsss are rtk gnss machine sensors such as odometers rtk gnss machine sensors inertial rtk gnss machine sensors inertial perceptionbased positioning and rtk gnss machine sensors inertial pseudolites ground based satellites or reference stations for belowground applications the most common types of positioning systems are radio frequency rf based distance measurement perception based positioning machine sensors and perception based positioning machine sensors inertial these positioning systems are well known in the industry perception based positioning systems have been used in restricted environments such as factory settings for more than two decades caterpillar 1991 and in underground mining applications for nearly a decade ferret 2003 rtk gnssbased positioning systems have been used to provide centimeter level accuracy in construction applications for a decade saghravani et al 2009 rtk gnsss are susceptible to poor gnss coverage and must be augmented to provide very high levels of availability unfortunately specific areas near the poles and areas with blockage to the east and west can have significant problems with gnss coverage however governments around the world have pledged strong support to the gnss infrastructure and as more satellites are put in service the gnss coverage should continue to increase substantially the most well proven technology to augment gnss for short durations is using inertial sensors plus odometry unfortunately this technology only has short duration accuracy other possibilities for augmentation include pseudolites often called ground based satellites or rf ranging beacons these systems allow individual mines to establish their own ground based positioning system which unfortunately can be very expensive to install and maintain clearly t

he more types of independent positioning sources that are available the more robust the positioning solutions will be perception autonomous machines generally need a good understanding of their surroundings to accomplish object detection and sometimes assist with positioning the perception system usually requires information from the mine model and the positioning system to accurately determine and report the location of objects perception sensors can come in several different forms radar laser vision and sonar not discussed here radar has been used since the early 1900s to detect ships and large metal objects more recently millimeter wave radars have been developed to detect objects for adaptive cruise controls and autonomous machines radar has the advantages of long range and seeing through dust and fog however radar suffers from relatively poor resolution when compared to laser based systems the size of an object that can be detected depends on the object s radar cross section rcs defined as the projected area of a sphere that would return the same signal to the transmitter the most effective means to increase the effect of rcs is to install corner reflectors commercial units are sold for small boats to improve their detection ability by radar corner reflectors can be thought of as tail lights for radar transmitters laser systems provide the best resolution but suffer from obscurants such as dust and fog newer lasers overcome much of this limitation by using multiple reflections from each point or from time gating the return to ensure that small diffused particles dust fog rain and snow do not obscure other objects as the density of particles increase the effectiveness of this method diminishes as with radar retroreflectors such as tail lights or reflective tape can be added to targets to greatly enhance their visibility to laser vision has significant promise for low cost object detection and object recognition that is most like human perception there has been a tremendous amount of work in this field and rapid progress is being made but so far vision is limited to relatively short range applications vision also is sensitive to shadows dust fog rain snow and reflective surfaces e g a reflection in a puddle may be confused as a real object combining multiple spectrums has significant advantages for example combining radar and laser gives the longer range and improved penetration of radar with the laser s ability to detect smaller obstacles and improved object classification as another example combining laser and vision allowed the terramax team in the grand challenge competition mentioned previously to recognize tumbleweeds in the desert that stumped a vision only system in earlier tests broggi et al 2010 unfortunately there are currently no practical standardized tests by which to easily determine the capabilities of object detection systems under all conditions another consi

deration for the practical use of autonomous systems is that none of the obstacle detection systems available today have the ability to differentiate a pile of small loose rocks e g a windrow left by a motor grader from a single large rock that could damage tires task level planning task level planning is defined as establishing a sequence of task or behaviors to accomplish a goal and is generally rule or constraint based as expected task planning varies significantly based on the type of goal the number of constraints the variability of the environment and the flexibility of the automated system one of the common machine level planning tasks is object avoidance primitive execution executing planned primitives is the fundamental machine operation some examples include drilling tramming loading grading stability control dumping and ripping these operations generally require continuous closed loop control and are probably the closest machine operation to a human skill exception handling handling exceptions is the ability for an autonomous machine to recognize that it does not have the means or required primitive ability to handle the existing situation and thus it resorts to fail safe behavior usually stopping and asking for help the building blocks for autonomous haulage system technology have been developed over the past two decades to the point where commercially viable automation systems for underground mining are now available and commercially viable haulage systems for surface mines will be available within the next few years in the near future autonomous and intelligent remotely operated machines will provide the opportunity for remote operations centers that allow miners to work in the relative comfort and safety of an office environment these first generation systems should rapidly evolve to provide continuous improvement in efficiency productivity and machine availability autonomous surface dump trucks one of the principle benefits from using fully automated dump trucks adts is the direct reduction of labor costs penman 2002 found that for two axle dump trucks in the 220 t metric tons class labor accounts for approximately 25 of operating costs fuel approximately 45 and tires approximately 30 for the larger 300 plus t class truck penman found the approximate cost split is labor 15 fuel 30 and tires 55 other benefits include improved safety through the removal of operators from hazardous areas and reductions in machine duty rate of accumulated damage and fuel consumption through more consistent operation for example the world s first fully automated straddle carrier system at the port of brisbane has reduced energy costs per container move by 40 kalmar industries 2007 the enabling technologies navigation truck control and collision detection for adts exist in a semimature form and prototype adts integrating these technologies have been developed and tested commercial ad

t systems are not yet available of the major haul truck manufacturers komatsu and caterpillar have both developed and demonstrated autonomous dump truck technologies komatsu currently has two sites operating its adt technology called frontrunner codelco at its gabriela mistral mine in chile has been operating 11 autonomous haul trucks since 1997 more recently rio tinto at its west angelas mine in western australia has been operating five trucks since late 2008 cribb 2010 both sites are using 930e 4 electric drive trucks with a payload of 300 t and the trials are intended to test autonomous trucks in high production scenarios in both cases the adts are not working on the same haul roads with manually driven trucks komatsu s frontrunner autonomous haulage system operates as a comprehensive fleet management system for mines the haul trucks are equipped with vehicle controllers high precision gps obstacle detection technology and a wireless network communication system the system has the capability to navigate a haul route dump automatically to hoppers or to the ground and work with some but not all loading equipment the system leverages off several mature technologies notably the gps and inertial navigation systems for navigation and millimeter wave radar and laser systems for safety and collision detection these technologies are integrated using largely fixed automation strategies trucks navigate from a so called pit database which serves the purpose of a haulage map and contains largely geometrical information notably the boundaries of the haul road the truck s travel path and the boundaries of the loading and dumping areas the boundaries represent the extent of the adt s allowed safe operation and are established by driving a light vehicle fitted with highprecision differential gps around the haulage perimeter the safe working area boundaries in load areas are updated as the shovel moves as an adt is manually driven along the required haul route at the required speed the truck s control computer records position speed and direction defining the truck s travel path the truck s control system steering braking engine and dumping functions has the truck replay this path to navigate from the load area to the dump zone and back again the use of the teach replay approach used in current adts simplifies the problem of planning the truck s course or path the truck doesn t need to plan its path it knows its path having learned it in the training run the repeatability of the replayed paths under this approach is high but it is necessary to add dither a small error in truck path control so that the truck does not always follow the exact same path on the road for every trip thus causing wear over a broader surface of the road to the steering action to distribute road wear a central control computer manages the adts on a particular haul each adt continuously communicates key data position speed

and heading back to the central control computer which provides general haulage management including tracking each truck s trajectory and anticipating collisions an onboard safety and collision avoidance system based on millimeter wave radar and laser sensing technologies is used this system has an overriding authority to bring the truck to a stop if an obstacle or safety hazard is detected automated underground loading and haulage in underground mines the restricted environment in which equipment operates has aided in its automation in addition some of the greatest potential hazards to miners occur when operating in and around underground mobile equipment this was an early driver to automate primary underground mobile materials handling equipment load haul dump units lhds and trucks operating underground follow well defined routes in repetitive operating cycles these coupled with a wellstructured underground operating environment made deployment of early autonomous vehicle technologies feasible as early as 1988 king 1988 predicted a positive economic return for the use of semiautonomous lhds caterpillar global mining 2008 describes recent trials of automated lhds at the malmberget mine in sweden showing an increase in productivity of between 10 and 20 autonomous lhds and underground trucks are now available from several manufacturers these are the caterpillar minegem system caterpillar global mining 2008 sandvik s automine system and atlas copco s scooptram automation system at this time more than 10 mine sites worldwide are operating or plan to operate either or both autonomous lhds and underground trucks these include de beers finsch diamond mine in south africa faurie 2007 codelco s el teniente mine in chile and the stalwell gold mine in australia caterpillar 2007 both systems have the underlying premise of removing the operator from the machine to a remote operating station where the machine can be teleoperated this station could be located underground on the surface at the mine site or at some distant location operation requires onboard cameras computer control of machine functions steering braking acceleration bucket motions lhds etc high speed network communications and associated safety systems however simple teleoperation is stressful for operators and less productive than manual operation the solution is operator assisted automated steering during teleoperation here the operator does not physically steer the system but views the machine s location in real time on a mine plan typically on a computer screen and then uses a joystick to give the machine the direction of travel in caterpillar s minegem system this is called copilot mode finally in autonomous mode the remote operator provides a goal for the machine lhd or truck and the selfguidance system controls the vehicle in caterpillar s minegem system this is called autopilot mode typically the operator fills th

e lhd s bucket in remote mode and then enters autopilot mode to tram to the dump point empty the bucket and return to the loading point thus in autopilot mode several machines can be operated by a single operator for safety reasons remotely controlled and autonomous machines need to operate in exclusion zones that strictly control access the key to operator assisted automated steering and autonomous navigation for lhds and trucks is the use of a laser radar range sensing system this system maps the location of objects typically walls around the machine and determines their location by comparing the measured profiles to an existing database provided from the mine map this technique is known as simultaneous localization and mapping thus knowing the location on the map relative to the nearest walls the control system can drive the lhd to the desired location automated dozers dozers are typically used for a wide range of applications in mining these include profile construction cleanup around other machines ripping and utility work thus the level of complexity required to automate a dozer is very much a function of the individual task needs such as the following examples adjusting ripper depth and angle and dozer speed and direction to ensure good ripping performance is key for an automated ripping dozer here interaction with other machines is often limited in many cases dozers create structured profiles for other machines to work on or from here material movement accuracy may be important dozers that undertake utility work such as dragging pipes and cables moving power boxes and pushing scrapers may have dedicated sensors and automation capabilities here the dozers require the ability to rapidly move from one application to another interaction with other machines and detecting where and what to clean up is important for dozers required to undertake cleanup tasks an automated dozer would have to detect when and what to clean up and interact with other machines shovels trucks etc in a variety of modes the automation of dozers to remove operators from machines appears feasible for dozer operations where interactions with other machines is limited and complex sensing and recognition of subtle changes in the machine s environment are not required these cases do not require development and use of complex sensing systems advanced automation infrastructure or control of complex machine material interactions automated dozers are not commercially available today several original equipment manufacturers oems and thirdparty providers have gps based dozer operator aids these include from caterpillar for example an in cab display that gives operators easy to understand color diagrams of where to cut and fill the system uses onboard computers software data radios and centimeter level gps receivers to constantly monitor work and update the plan caterpillar 2006b remote control solutions have a

lso been available for dozers for many years these are typically retrofits by third parties research into better solutions for remote control dozers continues a recent project funded by the national institute for occupational safety and health in the united states developed a remote vision system for dozers on coal stockpiles the project involved consol energy and caterpillar as participants this work is described in schiffbauer et al 2007 many of the enabling technologies dozer control positioning and navigation for automated dozers have been used in remote control applications for some time and therefore exist in a semimature form it is expected that automated dozers with the complete capability to build profiles clean up and rip will be achievable in the next 5 to 10 years dessureault et al 2007 and holmes 2006 describe an automated dozer project at freeport mcmoran s san juan arizona united states test site the target application for this dozer is ripping the dozer sensors include gps sick lasers and cameras for teleremote operation automated blasthole drills automated blasthole drills abds have the potential to generate a number of benefits these include reductions in machine duty rate of accumulated damage through smoother computer controlled operations and improved blasting performance through more accurate and consistent drilling reduced labor costs and improved safety through removal of the operator from a hazardous and dusty environment automation can also optimize drilling performance through control of bit loading drill rpm and torque parameters increased penetration rates lower bit wear and reduced drill costs will result it is also desirable that holes are drilled at locations specified by the designed blasting pattern inaccurate holes can lead to poor blasting fragmentation inappropriate muck pile shape for loading and so on abds also have the potential to generate benefits that include implementing drill based high level rock recognition systems to provide detailed rock type and structure information that can be used in blast design consistent drill operation through computer control of the drilling process enables these systems to operate effectively thus the enabling technologies navigation drill control and remote control for abds have existed in a reasonably mature form for some time prototype abds integrating these technologies are currently under development holmes 2006 describes the development in 2005 of an automated blasthole drill called the advanced rotary drill vector automated radio control ardvarc holmes states preliminary results of ardvarc trials as compared to normal manual drilling operations has shown a 15 productivity gain improved pattern and hole quality and lower machine duty cycle additional gains achieved from hole to hole positioning are expected the technology was tested on a be49r drill but has been transferred to the atlas

copco pv271 drill rio tinto has also been developing an automated blasthole drill that is currently operating at its west angelas iron ore mine the outcomes of this project are described in detail later in this chapter this machine is designed to drill automatically in both rotary and rotary percussion modes in addition the drill is capable of performing rock recognition during the drilling process in order to build a rock mass description of the area to be blasted this description is then used in the blast design process this drill also has full video remotecontrol capabilities the typical attributes of autonomous blasthole drills currently under development are automatic drilling of the hole from collaring though pipe removal when either manned or autonomous navigation from hole to hole within a drill pattern completion of drill pattern autonomously including accurate setup relocating holes due to hole failures or impossible collaring inclined holes and drill bit changes high level task instructions from a drill and blast management system monitoring of self condition e g airflow and pressure oil pressures rpm component failures and appropriate reaction e g report bit failure back to drill and blast management system monitoring of drill parameters thrust rpm vibration and other active and passive geosensors and using this information for rock recognition information that can be fed into a drill and blast design system and video remote control of all drilling functions remote operations centers a remote operations center roc enables supervision control analysis and data acquisition from afar in simplest terms an roc can be regarded as a platform for enabling process automation and business integration an roc enables enhanced occupational health and safety by removing operators and maintainers from risk exposure reduced labor costs by relocating high cost knowledgeintensive labor away from mine sites to urban centers increased productivity through identification of inefficiencies at operating interfaces collaborative planning between functions operations maintenance and procurement sharing of experience and knowledge across mine sites process visibility along the process chain and potential to lock in benefits through knowledge capture and reuse implementing an roc provides an important catalyst for change within an organization current workflow patterns must be evaluated and modified or adapted implementing rocs therefore provides an important stimulus for changing work practices and driving an organization to achieve higher levels of labor productivity interest in applying rocs is growing within the mining industry examples of early adopters within the mining industry are rio tinto iron ore rtio in western australia and freeport mcmoran in their arizona united states operations schweikart 2007 outlines the business drivers for rtio s implementati

on of an roc high cost of supporting remote staff desire for increased staff retention business integration faster better decisions the roc will also supervise the autonomous systems operating at rtio s west angelas iron ore mine site a fleet of five autonomous 320 t komatsu haul trucks are operating at west angelas as well as one automated blasthole drill rig trounson 2007 the removal of the need to maintain a large work force on site saves ancillary camp expenses remote working allowances and fly in fly out expenses which can account for significant costs additionally integration of operations site transport and infrastructure in one center removes silo mentality where people are focused only on the component of the operation they are involved in and fail to see the effects on the whole mining process creating bottlenecks at interfaces improved telecommunications infrastructure in particular telephone networks and fiber optic links are cited by dicker 2007 as key technology enablers for the roc development rtio is evaluating the remote support of maintenance personnel via head mounted displays and wearable computers support would make extensive use of video conferencing remote desktop access and voiceover ip technologies rtio is also evaluating remote collaborative planning via the use of augmented reality virtual reality based on real sensor information and touch tables schweikart 2007 tegrated operations the first step of this plan is to integrate disciplines planning operations and maintenance functions at site level and to begin the transfer of people from site to roc the second step is integration per asset site operations integration through the transition to remote operation and deployment of operations models the third step is integration across sites because of safety concerns and relatively static operating environments it is likely that roc technology will be implemented first on fixed assets such as beneficiation plants rtio is investing particular attention to aspects of change management and reevaluation of workflow scweikart emphasizes that changing to a remote supervision and operations model necessitates a change in the way that work and information flow is managed and that replicating existing workflows may not improve productivity coyle and holmes 2007 indicate that the installation of freeport mcmoran s roc on site was justified on the elimination of inefficiencies across operational boundaries the roc is also seen as playing an important role in institutionalizing the knowledge of maintenance and operations experts here the vision of the future has tactical operations personnel co located in a room of truth verified information is made available on a real time basis so that subject matter experts can assist less skilled operatives in the field crosspollination of ideas and shared operational awareness are forecast to lead to significant efficiency gains

for the organization automated digging large capacity shovels and hydraulic excavators called diggers in this section with bucket capacities to 70 m3 are critical production units at most open cut mine sites and there is an ongoing imperative to improve their productivity automation is seen as one of the strategies by which improvements can be realized the automation of diggers presently stands at an interesting nexus most of the technology needed to realize the automated digger exists albeit at varying levels of maturity and developments in other sectors including industrial robotics and the automotive and aerospace industries are delivering further advances that enhance technical feasibility however the cost and risk of introducing automated diggers to mining operations currently outweighs the perceived benefits an automated digger must operate as part of the overall operation of a mine with implications on mine infrastructure operational practice work force skills and site culture the gap is significant and no mining company is actively pursuing the introduction of automated diggers to their operations notwithstanding the several significant mine automation initiatives taking place worldwide e g rio tinto s mine of the future at the west angelas mine site the transition to automated diggers will likely occur over the next 20 years it will almost certainly be staged through incremental stepping stone technologies that in themselves bring productivity and reliability benefits and allow the risks to be understood and controlled and the technology to mature and be proven and accepted in mining environments this section attempts to identify at a fairly high level automation capabilities that might serve as planks in the bridge to realizing the autonomous digger over the next two decades capabilities of the autonomous digger the autonomous digger excavates material and loads trucks with minimal human intervention plans and executes repositioning moves using high level mission statements referenced to the mine plan feeds up to date information garnered from onboard sensors back to the mine plan including terrain information material diggability and productivity indicators manages the dig face and floor to optimize productivity and maintain favorable bench structure automatically executes ancillary functions including management of the trailing cable on electric shovels machine park up for access and so on has advanced status monitoring capabilities to identify situations associated with the machine or the environment requiring attention this includes monitoring structural and electrical heath trends for early prognostication of events and failures manages overall activity in the load area including the scheduling and dispatch of trucks cleanup activities and so forth and provides an information rich teleoperation mode that allows recovery from exceptional situations to be completed remot

ely benefits of the autonomous digger the benefits of the automated digger stem from the increased consistency and reduced variation that automation brings to equipment operation resulting in productivity and reliability improvements and the ability to have the machinery operate under its most favorable conditions ultimately this translates to increased productivity with lower production costs and energy consumption the business case for the autonomous digger is likely to be built around the following benefits consistent and accurate loading of haul trucks when trucks are loaded to their rated payloads and the load is correctly distributed across the tray then the chassis transmission and tire life are significantly improved and operating costs reduced increased digger availability automation brings consistency that stands to increase equipment availability through lower duty loadings safer operation most safety incidents associated with diggers are linked to operator error e g digger truck collision by marginalizing the root cause automation has the potential to reduce the frequency of accidents and near misses technology gaps four broad technology gaps must be bridged to realize the autonomous digger 1 control strategies must be developed to enable automated machines to operate interdependently with other equipment manned and automated 2 situational awareness capabilities must evolve to the point where they can replace the many and varied functions currently performed by human operators in planning and actions and monitoring the status of the machines 3 technologies are required that enable effective integration of automated machinery into mine systems 4 work force skills must be enhanced to support deployment of high end automation technologies a significant component of the shovel automation problem is systems integration including management of interactions with trucks and other equipment and integration of the autonomous shovel into the mine plan although in the long term there will almost certainly be multiple technology providers working to agreed automation standards at this time the problem is not sufficiently well defined for effective standardization efforts the likely scenario for the short to medium term is that various equipment and technology providers will integrate their proprietary systems by ad hoc methods on an as needed basis under pressure applied by the end user the mining companies or one provider will come to dominate the market and set a de facto standard for integration the long time horizon for achieving a fully automated digger system mandates a multigenerational technology plan with commercial outcomes that prove technology components and support and maintain the development effort toward its end goal figure 9 8 1 gives a digger automation capability plan to 2025 with capabilities divided into three categories 1 machine situational awareness capabilities these incl

ude such things as machine performance monitoring functional safety capabilities support automation requirements electrical and structural health monitoring 2 shovel automation capabilities these incrementally build from operator assists such as collision avoidance tools through automated digging to management of the load area 3 load area situational awareness capabilities these build an evolving richer situational awareness model of the load area with knowledge of digger and truck positioning at the lowest level building toward the full perception of elements in the load area the comprehension of their meaning and the projection of their status in the near future implicit in this capability map is that machine and load area situational awareness capabilities feed into shovelautomation capabilities the timeline is indicative as is the ordering but it is generally expected that capabilities will flow in this order the plan has been organized so that each identified capability could in principle serve as a commercialized outcome the continual delivery of technology products that have productivity or maintenance benefits in their own right and contribute incrementally to the autonomous digger represents the only practical strategy r d based innovation at all levels of the plan is strongly needed and the most likely scenario is that r d will be completed by consortiums made up of an equipment manufacturer the end user and one or more thirdparty technology providers including research organizations and universities current state of automation fully automated shovels are not commercially available however shovel automation has been the focus of extensive research over the past few years dunbabin and corke 2006 describes automation work completed on a 1 7 scale model cable shovel that demonstrated the ability to automatically perform multiple truck loading passes that included excavation of the dig face swinging with obstacle avoidance identifying an awaiting truck tray determining an optimal loading strategy and dumping the material mcaree et al 2007 describe collaboration between the cooperative research centre for mining crcmining and p h to develop advanced technologies leading toward shovel automation a p h crcmining laboratory has been set up in a quarry north of brisbane australia and includes a full sized p h 2100ble electric cable shovel this laboratory is used to develop and evaluate technologies that increase the productivity of electric mining shovels the australian coal association research program acarp is currently funding a project to develop to proofof concept an automated swing loading technology for electric mining shovels at this facility a joint crcmining and australian commonwealth scientific and industrial research organisation csiro team are developing technologies for a shovel that cycles the swing dump and return functions this includes automatically identifying the location

of a truck or in pit crusher conveyor to be loaded planning and executing a minimum path from dig to dump location without the dipper colliding with the truck crusher or bank and dumping without spillage and swinging back to tuck position for the next dig automated digging is probably the most complex component of loader automation automation technologies to assist digging are commercially available for several of the autonomous lhd products but not for large surface loading machines a considerable body of research in automated digging exists singh 1997 hemami and hassani 2009 and lever 2001 provide reviews of this research area longwall automation two basic control systems exist in a longwall operation one control system operates in the horizontal plane to control the plan view geometry of the longwall face and the second operates in the vertical plane to control the roof and floor cutting horizons within the coal seam added to these functions are systems for armored face conveyor afc control including chain tensioning and load sharing and shearer haulage control in simplest terms in plan view the longwall face should be straight and perpendicular to the gate roads if the face is straight both mechanical stresses on the armored face conveyor and roof support geotechnical issues are minimized the process to achieve this situation is known as face alignment as the longwall retreats the assembly of supports should not creep toward either main or tailgates to achieve this result in practice often the face line is angled introducing so called tailgate lead or lag with respect to the main gate so that in sloping seams the same creep minimizing result can be obtained managing the lateral position of the longwall equipment in the panel is called creep control automatic face alignment and automatic creep control are two functions that can be applied to effectively provide automation of longwall plan view geometry available systems are discussed in this section in the vertical plane the automation situation is more complex the goal of the longwall similar to any mining operation is to maximize extraction of product and minimize extraction of waste this means the longwall shearer should operate so that roof and floor cutting horizons are entirely within the seam or in some cases within a selected band within the seam achievement of this goal is known as horizon control automated horizon control needs to at least emulate and at best entirely replace human operator strategies for steering the shearer within the seam again the available automation solutions for horizon control will be discussed undeniably longwall automation has the potential to deliver significant advantages in both productivity and safety henderson 2007 interruptions to the mining process are basic causes of decreased productivity continuous automatic face alignment for example can virtually eliminate stoppages caused by current s

tring line based manual alignment processes and optimal alignment of afc components minimizes wear and reduces consequent equipment breakdown or change out delays close control of face geometry can also improve geotechnical performance of the roof support system where an automation system can ensure that shields are set consistently automatic horizon control can more effectively steer the longwall in the seam to minimize product dilution and can also contribute to more effective strata control by accurately leaving coal on the roof and or floor to protect weaker strata in the safety context automation provides the ability for the mine to remove people from hazardous areas minimizing exposure to dust heat noise and danger from roof and face falls automatic face alignment and creep control automated face alignment is now a mature technology and all longwall roof support manufacturers offer systems that deliver effective face alignment automation solutions these systems allow desired face profiles to be entered into shieldcontrol systems through appropriate graphical user interfaces and shield control systems are capable of moving individual shields by calculated distances and are thus also able to coordinate the motion of assemblies of shields to achieve desired profiles along the entire face shield hydraulic control systems have been enhanced to allow accurate control of double acting d a ram motion and sensors to reliably measure d a ram travel have been incorporated into shield designs until recently the major defect in automatic face alignment has been the inability to automatically and reliably measure the actual geometry of the longwall true closed loop control of face alignment can only be achieved by comparing the physically measured location of the face with the target location and then minimizing the resultant error previous methods were largely based on measuring the accumulated motion of shield d a rams to indicate face geometry which gave only an approximate solution with increasing accumulation errors this situation has been remedied recently through the development of the lasc longwall automation steering committee technology which measures three dimensional shearer position directly through an inertial navigation based spms shearer position measurement system because the shearer actually cuts the face direct measurement of shearer position is the best indicator of face geometry open specifications for spms data outputs have been devised enabling lasc technology to be applied to any combination of face equipment the reader is referred to www lascautomation com for details of lasc specifications and more detailed lasc technology descriptions all face equipment manufacturers now offer lasc technology to the market sensors that measure the position of longwall face equipment relative to the gate road ribs can be used to provide a measure of automatic creep control if motion of gate end equipment relat

ive to the ribs is detected appropriate lead or lag of the face can be introduced into the basic face geometry input to the automation system although lasc laser based creep sensors are now available to provide this measurement transformation of this information directly into tailgate lead or lag values is highly site dependent and requires operator input face alignment control system example contemporary graphical user interfaces guis for longwall roof support control systems can be used to display the state of sections of a complete longwall face that can exceed 200 shields in current operations they can also display the leg hydraulic pressures this display gives immediate information regarding the hydraulic performance of the supports and can also show through color change when particular shields are not set correctly or are being excessively loaded by the roof strata when the face has become misaligned with respect to the target face line it is seen as an uncut wedge developing between the desired profile of the unmined coal and the afc to realign the face a wedge cut must be executed in the current shearer run to realign the supports perpendicular to the longwall block this is achieved by making proportional changes in the shield advance distances programmed to introduce a compensating wedge shape in the face eliminating the misalignment as the shields advance after the shearer passes the success of this kind of control depends on accurate measurement of face profile and d a ram extension as outlined in this chapter it is difficult to accurately quantify productivity benefits due to contribution from specific automation system elements however in the case of lasc based face alignment sustained productivity improvement of 130 t h was reported reid 2008 other productivity improvement information is company confidential to individual equipment suppliers automated horizon control longwall horizon control manual or automated is a challenging task whereas the overall goal of horizon control is to ensure that as far as possible only coal is extracted there are a multitude of site specific considerations that detract from a mine s ability to achieve that goal it might not be possible to detect seam boundaries effectively in order to prevent the shearer drums from cutting surrounding rock in the case of thick seams where visible or other cues to indicate seam trajectory are absent it is difficult to steer on a consistent path between the gate roads in other cases seam undulations along the face or into the panel might mean that equipment cannot articulate sufficiently to track the actual horizons and roof or floor is cut as a consequence problems in detecting fault conditions ahead of mining could mean it is necessary to mine through the faulted zone at short notice automation of horizon control is in the developing stages the most successful strategy so far has been based on training an automation system using a hum

an operator employing traditional manual cues for horizon detection and control to steer the shearer the learned extraction process is then repeated automatically until some departure from the horizon control strategy is observed such as roof or floor being cut the training process is then repeated the advantage of this process is that operator exposure to face conditions is at least reduced the accuracy of this process has been improved by the availability of the lasc technology which gives high accuracy floor horizon measurements all shearer manufacturers offer systems that are variations on this basic strategy the next stage in the process is to use sensors that can replace the horizon sensing capability of human operators or bring to bear new horizon sensing results coal interface detection cid sensors based on natural gamma emission by surrounding strata thermal infrared detection groundpenetrating radar optical marker band tracking and other methods have been developed with varying results the only commercial cid sensors currently available are based on natural gamma radiation and detection of electromagnetic propagation differences between coal and surrounding strata several of the other methods are still in the research stage figure 9 8 2 shows a gui for an interactive automated horizon control system based on the lasc technology the gui accepts and displays horizon information over the full face length the upper screen enables an operator to enter adjustments to a nominal extraction height setting that has been independently set in the shearer control system the flat line shows that no operator adjustments have been selected the lower screen enables the operator to view recommended floor profiles and to input adjustments manually the system then automatically generates lasc recommended floor height adjustment for the next complete shearer run in its simplest form this adjustment is generated by extrapolating the average floor profile from the previous five shears at this stage of development of automated horizon control the operator is in the loop the operator has the ability to input manual floor height adjustment on a per shield basis the operator s task is to input manual horizon inputs to match the recommended profile as closely as possible the operator is also able to take into account off system inputs such as physical observations along the face or known conditions that would preclude the shearer being able to execute the automation system s recommended track close matching of manual to automatic settings is shown on the left hand side of the display in figure 9 8 2 on the right hand side the operator has chosen a floor profile that does not closely follow the predicted floor alignment figure 9 8 2 shows the smooth profile that the automation system generates compared to the manual inputs this profile then becomes the floor height adjustment target for the oem s shearer control system state bas

ed shearer automation in recent years one of the most successful initiatives has been the development of programmed shearer automation on a logical state basis the concept is similar to the training method of horizon control described earlier the operating parameters required for the shearer to completely execute a single pass of a particular cutting sequence are defined as a series of logical states that encompass combinations of ranging arm positions haulage speeds and various sensor outputs including motor currents position measurements and so on as the shearer travels along the face it sequences through the previously defined states if no anomalous states are encountered the pass will be executed successfully and the machine will commence the next pass error states can be defined to handle operational exceptions but some errors will cause the system to halt when human intervention is required when this system was first introduced significant productivity improvements resulted immediately this was attributed largely to the consistency that was possible when operation was based on a fixed programmed sequence and not subject to variable operator inputs challenges to overcome the automation technologies described in this chapter are able to successfully automate the routine operations of a longwall the major problems encountered in longwall automation are concerned primarily with the management of exceptions to normal operations caused by the fact that an underground mine is actually not a factory environment and is subject to the vagaries of nature to achieve full automation and the workerless face many more sensors need to be developed to replace the observing roles carried out by face operators at present additionally there are issues with ensuring that equipment operates to the standards required for automation in a harsh hazardous environment mine requirements for longwall automation the face alignment and programmed shearer automation systems can be implemented in most mines in the case of horizon control it is necessary to establish whether local seam conditions exist that allow horizon sensors to be effective equipment manufacturers can offer advice as to which sensors will be appropriate for modern automation systems high quality data communications links to sensors and face equipment are required longwall manufacturers now provide ethernet connectivity on face equipment as a matter of course for these systems to be effective at a mine corresponding communications infrastructure must be available between the face the surface and wider into the mining company s and its service providers data communication networks future challenges a major challenge over the next decade is to automate the unit operations themselves understanding that some of the equipment in a group may remain under direct human control or be semiautomated thus each automated machine must be able to operate interdependently with th

e other machinery associated with the unit operation the absence of this capability currently is a major barrier to the deployment of automation technologies in mining understanding how to achieve safe interdependent operation in mixed fleets is the most important and significant technical barrier to the further development of mining automation technologies mcaree and lever 2003 provide recommendations for where investments in surface mining automation research will provide the short to medium term benefits to the mining industry while making progress toward full automation they are as follows advanced sensing technologies for the mine environment this includes the processing of sensor data to extract information and sensor fusion for combining data from several sensor sources imaging technologies for terrain and local area mapping are important as current technologies are sensitive to dust vibration and temperature variations use of mine wide information systems to facilitate unit interactions mine wide information systems play a critical role in controlling the interactions of automated equipment this task will be complicated significantly if common communications protocol is not adopted that would allow complete interoperability between sensors and mine information software from different vendors extended use of existing and new sensors aboard equipment data from onboard sensors can be used not only to monitor and report equipment status and performance but to develop detailed understanding of equipment operations and their interaction with mining processes understanding these operations is an important step for successful automation developing duty meters to manage the trade offs between equipment productivity and damage and to predict failures automation systems must perform the many maintenance fault detection and isolation functions that operators currently execute it is important to understand how machine performance and duty trade against each other to optimize the productivity of automated equipment poor availability poses the same problem for automated equipment as it does for manually operated equipment the widespread acceptance of automation and robotics technologies in mining over the coming decades will depend on a number of factors including simple and effective integration with mining processes changes to existing mining processes to simplify the use of automation management acceptance to ensure automation is seen as a benefit not a threat to the mining work force implementation occurring in stages starting with narrow domain or task requirements and then increasing capability and complexity machines then systems meeting mine requirements of productivity cost and flexibility balancing technical complexity with robustness transparent operation wherein mine personnel must clearly understand the capabilities and limitations of the systems and turnkey systems as much

as possible a major threat to the uptake of mining automation is the desire for a quick success which leads to shortcuts in technology development and poor implementations a view of automation and the mine of the future for decades visionaries have predicted that autonomous machines would be critical to the future of mining the major drivers have been safety the need to work in remote locations the lack of operators in general long term reliability improvement and efficiency gains these visions are rapidly becoming a reality safety advantages one of the most often cited reasons for autonomous mining is safety although the fatality rate published by the mine safety and health administration msha 2009 shows a reduction in fatalities significant improvement is still needed despite tremendous effort on the part of regulatory agencies mining companies and equipment suppliers the total number of fatalities in the united states has on average not improved substantially since 2003 similar statistics from australia south america and china show that further safety improvements are very challenging to achieve and potentially even harder to maintain one clear strategy to reduce injuries and to easily maintain the reductions in injuries is to remove people from harm s way for example it is estimated that automation and rocs offer the opportunity to remove up to 80 of haulagesystem operators from surface mines fewer people involved in mining operations translates to fewer opportunities for safety related incidents and fewer opportunities for long term disabilities caused by repetitive operations integrated site awareness another significant safety advantage provided by autonomous systems can be achieved through integrated site awareness or situational awareness probably the most easily understood example of situational awareness is the accident prevention provided by air traffic controls by tracking most planes and controlling corridors the situational awareness provided by air traffic controls helps reduce mid air collisions studies indicate that situational awareness can lead to substantially improved performance in complex military environments endsley 1995 although managing a mine or operating mining equipment may not be as complex as operating a military aircraft or as demanding as managing a battlefield the continual aroundthe clock nature of the mine operation makes site awareness just as critical figure 9 8 4 a well integrated mine of the near future will allow all machines and potentially mobile objects to be tracked in real time integrated site awareness will allow both automated and human machines to easily perceive and comprehend the current situation which should lead to better decisions and a safer environment for both no fatigue and minimized opportunity for operator error although recent estimates of the effect of fatigue in accidents vary considerably from 2 to 41 according to de gennaro et al 2001

fatigue is clearly recognized as a significant contributor to mine accidents furthermore operator error caused by all sources including fatigue may account for as much as 88 of all accidents heinrich et al 1980 it is commonly recognized that the best means to avoid accidents is to design out the opportunity for the accident using automated systems significantly reduces the opportunity for errors and provides a means to accurately track correct and control any remaining issues automated systems never get tired bored distracted or inattentive there will certainly be challenges related to performance in all environmental conditions but these should be well understood and will improve over time remote locations it is anticipated that many new mines will be located in regions with low population densities the cost to develop housing schools hospitals and other required infrastructure can significantly impact the ability for a given site to be a cost leader have a production cost below the average cost in the industry many remote sites are supported by a large number of fly in fly out fifo employees which can lead to fifo fatigue and potential higher turnover rates due to the variability in mining it is difficult to make accurate assessments informal feedback from the mining industry suggests that it costs mine sites 100 of an annual salary to replace a worker and a further 50 to train the replacement to a desired productive level rowland communication group 2004 the cost to attract workers and the worker turnover at remote locations can severely impact the operating cost production and safety at these remote mine site locations reducing the total number of workers via automation and allowing more of the remaining workers to work at rocs could significantly reduce fifo fatigue and may reduce employee turnover availability of operators scarcity of skilled operators during boom times is often cited as a major problem for mining expansion barta 2005 certainly mines that follow the volatility exploitation model essentially mines that are only operated during times of high commodity prices will make it difficult for the industry to maintain a stable highly trained work force using autonomous systems could minimize the volatility and reduce the start up and shutdown times of higher cost operations efficiency another key reason for interest in automation is the expected gains in overall relative efficiency where relative efficiency is defined as tons moved per day relative to a nonautomated mine with the same contingent of machines several factors can dramatically influence the efficiency gains at any particular site including load size cycle time speed queuing time spotting time loading time and dumping time accuracy percentage of loads delivered to the right location machine availability and operator availability discounted for training time breaks absence etc for haulage systems

these can be written as relative productivity relative load relative accuracy relative machine availability relative operator availability relative cycle time relative load autonomous machine load manual machine load expect this ratio to equal 100 relative accuracy this is the percentage of total loads waste and ore that are dumped in the correct location the relative accuracy should improve slightly for automated machines relative machine availability the percentage of time that the machine is down due to a mechanical or electrical failure it is assumed that machine availability will improve over time with automation due to the moreconsistent machine operation relative operator availability operator availability can vary widely depending largely on the local mining process this is an area of substantial potential gain for autonomous systems for example if an existing mine with no automation achieves 16 h d of actual working time and the same mine with an automated haulage system can achieve 22 h d of operation it is a 38 increase relative cycle time this is the average total time per cycle with an autonomous system divided by the average total time per cycle without an autonomous system relative cycle time includes the loading time transporting time dump time and queuing time for underground mining systems that are already using remotely controlled machines automation should provide a significant improvement in cycle time but for haulage systems that are currently using manned machines the relative cycle time may be lower for initial automated systems however due to the expected rapid evolution of autonomous systems it is anticipated that future generations will match the cycle times of well controlled mines that operate machines within their design limits in other words the machines will be operated according to their design limits and the mine rules efficiency gains though process control arguably the greatest potential improvement may be in process control the availability of machines that operate consistently and as instructed provides the opportunity for mine operators to fine tune their operations future mine systems will allow every machine person and process to be accurately tracked this will provide unique capabilities to accurately model all mine processes using real time models to improve mine planning capabilities the autonomous machine will be the most salient change but the real driving force for improvement will be the consistent predictable process coordinated by an information rich environment an example of a related industry is that of gradecontrol systems used in construction these have shown process control related improvements of 30 50 and associated fuel and carbon dioxide reductions of 43 caterpillar 2006a process control is expected to be a strong area of dramatic innovation as autonomous machines begin to be deployed although independent

data is not available a recent article regarding the deployment of caterpillar s minegem technology at the jundee gold mine in western australia states that minegem cut down on wear and tear on the machines according to gary mills jundee s mining manager what was happening previously too is that the boggers were bouncing off the walls and causing a lot of damage the laser driven boggers stay off the walls so you don t get any damage even though they can go faster the need for secondary stockpiles in the mine has also been removed by the faster tramming speeds cutting down that cost as well haycock 2009 challenges and changes required for successful automated systems clearly putting an autonomous machine into an otherwise unchanged mine will not provide the expected gains for example in general autonomous trucks will initially travel at slower speeds than human operated trucks causing significant loss of efficiency for the human operated trucks information system improvements one of the biggest changes will be the amount of information needed to run a mine smoothly an autonomous mine will be very much information driven including everything from the detailed mine model to product levels payloads and the location of every asset this will drive several requirements on communications and information infrastructure high bandwidth communications with quality of service capability will be a requirement it is strongly suggested to have dedicated communications channels to avoid issues with lost or late communications tracking and communicating the location of every asset will be a key layer of the obstacle avoidance strategy neither people nor machines should be allowed to operate within an autonomy zone without proper electronic tagging every asset will need to provide vital information such as its position heading health status destination detected objects and potential road map changes in addition it would be useful to communicate any potential changes about the road surface wet rough surface soft etc this information will be in addition to the existing productivity and maintenance information that is used for typical mine management accurate mine and machine model maintaining an up to date mine model will be absolutely critical to autonomous machines although machines should have secondary sensors to detect inconsistencies in the mine model autonomous machines will by necessity assume that the mine model is correct most machines should be programmed to halt if they detect inconsistencies in the mine model analysis of the inconsistencies and self correction would be the next phase of development for automated systems the definition of the mine model will require orders of magnitude more detailed than existing mine models that are used for automated assignments or dispatching all mining machines will have to be modeled as well the fidelity of the machine model will be dependent on the class

of machine such as autonomous machines interactive machines such as loading machines support machines and mobile platforms light plants pumps etc autonomous machines including both kinematic and dynamic models will need to be very accurately modeled interactive machines such as loaders will need to have a very accurate kinematic model and accurate positioning support machines may be modeled much more simply and mobile platforms may be modeled simply as an exclusion zone any significant changes to these machines will need to be tracked and modeled e g a pickup pulling a trailer suddenly appears to have grown in length required operational changes successful installation of an autonomous system will require operational changes in several key areas working environment obtaining consistent predictable productivity will require a reasonably predictable working environment anything that alters the working environment such as water trucks will need to be accurately controlled and monitored improved information system maintenance maintaining the electronic infrastructure will include positioning systems and dedicated high bandwidth communications systems in general automated systems will require either a dedicated network or a redundant network with quality of service assurance in addition a backup network should be installed for emergency and autonomy stop functions avoiding mixed fleets in general autonomous machines will travel at different speeds than human operated machines faster in some cases and slower in others and mixing manned and unmanned machines may cause significant loss of efficiency for the human operated trucks automated equipment may be programmed to be more sensitive to human operated machines potentially slowing down to avoid any risk of an accident and will therefore tend to be less efficient machine health and maintenance site level machine health monitoring will become more critical as autonomous machines become more prevalent in addition there are still items that are only detectable by human operators some vibrations noises etc development of new prognostics and diagnostics will be required and maintenance procedures will become much more critical automation capability the automation of the large surface blasthole rigs has advanced at a faster rate than the smaller articulated boom rigs larger rigs are considered easier to automate as they have fewer degrees of mast movement they are generally located in mines with large simpler patterns with generally vertical rotary holes the benches are generally well maintained and provide the ideal environment for navigation and leveling automation of rotary drilling is considered easier than hammer drilling hammer drilling requires a precise rotation speed that must adapt according to the penetration rate rotary drilling on the other hand will generally have a fixed rotation speed that does not vary as much with the geo

logy mine operators will always encounter different drilling environments and the more accepted automated drill systems are the ones that allow intervention either manually or remotely to deal with exceptions this feature is important as it generally allows little loss in production over completely manual systems aiding in system acceptance the automation of some ancillary functions of the drilling process will require significant engineering changes to occur such as bit changing and mode of drilling since these processes use consumables of the drill that wear quickly in the near term they are probably better handled in a semiautomated mode to make the drill ready for automation it is generally considered that the drill must be set up for electronic control many of the new surface drills use the controller area network bus that was developed for the automotive industry advantages of drill automation automation of surface blasthole drill rigs has demonstrated greater accuracy and repeatability with similar rates of productivity compared to manual operation remote supervision of automated drills has allowed one operator to control more than one drill field trials of a proprietary automated system on an 80 t terex skss16 rotary and percussion blasthole drill at the west angelas iron ore mine demonstrated significant improvements in accuracy over manual operation the summary of the results are displayed in tables 9 8 2 and 9 8 3 table 9 8 4 compares the same automated drill performance against five other same model drills operated at the mine in manual mode over a period of 9 weeks the remotely supervised drill was able to drill more than 90 of all holes in automation mode the high degree of repeatability of the automated drilling process allows mine operators to choose a drilling approach that best suits their operation with a high degree of confidence that the drill will achieve it the selected drill approach should ultimately help achieve the overall mine strategy the repeatability also helps mine operators to better understand the trade offs in different approaches the mine geology can have a significant impact on which approach is required at different areas of the mine and therefore it is unlikely that one single approach will be optimal in achieving the mine strategy approaches may include trading off production performance for improved drill bit wear rates drilling the straightest hole maintaining hole stability to prevent redrilling and lowering overall stress and vibration on the drill mast and chassis in a manual drilling operation expert drillers are those who can best follow the approach selected by management and adjust the strategy according to the changing geology and condition of the drill the automation of these approaches will generally reduce the time required to train a new operator to perform like an expert driller figure 9 8 5 is a comparison of a manually drilled hole and an automated hole

drilled 5 m apart in the same geology the automated drill shows the correct amount of water injection to maintain a stable collar in that geology disadvantages of drill automation although the advantages of automation are significant there remain some disadvantages the automated drill is best suited to stable geology it can be slower than certain parts of the drill cycle as it maintains the level of accuracy required sensor failure on the drill is common and could stop the whole system without significant sensors and processing the drill may not detect the changing drilling environment such as collapsing collars collapsing holes collapsed bench edges obstacles such as rocks fallen on the bench and potential interaction with other equipment such as explosive charging carriers detection of worn bits or drill string failure can be difficult high precision gps may be difficult in deep pits and may require ground based satellite augmentation challenges to overcome to improve the function and reliability of automated systems several factors need to be addressed provision for reliable sensors capable of withstanding extreme conditions experienced on the drill if operating remotely reliable wireless communication with significant bandwidth the use of prior geological knowledge to adjust the automated settings adequate vision coverage to supervise the rig remotely complex movement path planning between rows integration with other mine equipment such as explosives trucks advances and productivity wireless communication for supervision of automated drills enables the use of other real time sensors for purposes such as rock recognition automated sampling and downhole sensors prior knowledge of the rock behavior could be incorporated into the automated function design the use of remotely supervised automated drills enables the operation of at least two drills at once as automation becomes more reliable and remotely supervised it should be possible to run more than three units with one operator the term mine infrastructure refers to major capital installations at surface and underground mine sites mine infrastructure is very site specific and depends on the mine location size mining method equipment used and work force it includes access roads and declines hoisting and ventilation shafts and equipment drainage and pumping facilities backfill preparation and delivery systems power generation plant and distribution systems workshops service and warehouse facilities offices changehouse chilled water plant wastewater management systems and construction facilities other on site infrastructure includes ore treatment plant and laboratories communication networks and equipment for automation of mine operations the primary objective of mine infrastructure maintenance is to ensure that production targets are met on time safely and economically modern mining is mechanized and automated req

uiring a high level of availability and reliability of mine infrastructure and maintenance preparedness to ensure that operations are maintained at designed mine capacity the mine production system is critically dependent on the availability reliability and capacity of mine infrastructure the substantial level of system integration in modern mines has elevated the criticality of mine infrastructure furthermore mechanized and automated mining systems are expected to safely perform at designed capacity around the clock making access difficult for maintenance workers and complicating the task of maintenance scheduling because of the diversity of solutions to specific infrastructure requirements this chapter will not detail maintenance requirements for all types of infrastructure rather it concentrates on general principles of infrastructure maintenance management and presents some of the critical issues and challenges related to maintenance of the following systems hoisting systems underground roadways electrical power distribution systems mine dewatering systems maintenance workshop facilities performance of infrastructure availability and reliability performance is the commonly used measure of infrastructure performance maintainability performance is the universal measure of the maintenance friendliness of the infrastructure availability and maintainability are not only measures of system performance but they also have considerable influence on the financial performance and success of mining businesses availability designing and using infrastructure systems that are maintenance friendly significantly improves safety and system availability availability of infrastructure means that infrastructure is available for delivering the services for the specified period of time in general infrastructure availability can be defined as total scheduled time for service available time for service the international electrotechnical commission iec 2010 defines availability as follows the ability of an item to be in a state to perform a required function under given conditions at a given instant of time or over a given time interval assuming that the required external resources are provided availability performance is described by the collective term dependability and is a function of reliability performance maintainability performance and maintenance support performance as illustrated in figure 9 9 1 reliability and maintainability are design characteristics of the infrastructure that are determined during the design and development phase of the system s life cycle maintenance support on the other hand is dependent on the users organizational and operational need including their operating environments these factors influence the risks or uncertainties related to the availability and capacity performance of the mining infrastructure a high availability performance level is an important and critical requirement for

most of these systems the factors influencing availability and capacity performance of mining infrastructure include reliability maintainability and maintenance support figure 9 9 1 even though high operating reliability characteristics are desirable to reduce the costs of maintenance and maintenance preparedness the benefits of improved maintainability should not be overlooked in achieving the required availability performance high maintainability performance makes a system easy to maintain and repair resulting in high availability performance see kumar and akersten 2008 reliability the reliability of a system is a measure of the probability of its survival as a function of time in the mining industry mean time between failures mtbf is often used as a proxy for measuring system reliability where failure is defined as unscheduled downtime due to equipment not process malfunction block models are often used to model the reliability of systems systems can be characterized according to whether their principal components are series or parallel connected in series connected systems the failure of one component causes the entire system to fail this is typical of longwall systems where for example the failure of the face or main gate conveyor disrupts coal production parallel systems are designed with some redundancy for example a mine dewatering station should include at least one standby pump should the main pump fail the standby can be activated to prevent flooding the mine infrastructure elements listed previously are either common components to production systems see figure 9 9 2 or are series connected and so many items of mine infrastructure rate highly on the scale of critical systems for maintenance purposes for example every component in a longwall mining system requires power to function failure of the power distribution system will cause all components to fail a mine hoist is a very important series connected element in the productive system loss of hoist capability will result in production losses and could jeopardize the future of a mine depending on the extent of the downtime required to restore functionality maintainability high maintainability performance and in turn high availability performance is obtained when the system is easy to maintain and repair in general maintainability is measured by the mean repair time often called mean time to repair mttr which includes the total time for fault finding and the actual time spent carrying out the repair the way in which an infrastructure system is designed and built has a direct bearing on the maintainability of the system capacity many of the mechanized and automated mining operations are expected to perform safely at designed capacity most of the time or around the clock making it extremely difficult for infrastructure engineers and managers to get a time slot to maintain them so as to guarantee a high level of reliability availability

and capacity the issue of possession of mine infrastructure for maintenance is critical in a mining system operating 24 hours a day and seven days a week it is also important to define the capacity of infrastructure it is possible for infrastructure to be available but the prevalent operating condition or physical condition may restrict capacity for example a mine hoist may be forced to operate below rated capacity because worn guide rails restrict hoisting speeds similarly a poorly maintained haul road can restrict speeds and lower transport capacity roads may be filled with potholes or a lack of water for sprinkling may mean a lot of dust is generated reducing visibility for truck drivers and forcing slower operations maintenance of roads haulages and other infrastructure systems directly affects their capacity therefore it is important to measure the performance of mine utilities and infrastructure in terms of both availability and capacity to ensure adequate availability and capacity high levels of reliability maintainability and maintenance system support maintenance tactics maintenance tactics sometimes called maintenance policies or maintenance strategies are defined on the basis of failure type and consequences of failure four basic classes of tactics are available for implementation 1 reactive tactics are run to failure policies that is repair only on breakdown this approach is also known as corrective maintenance 2 preventive tactics are interval or time based maintenance activities and include inspections lubrication adjustment calibration cleaning component replacement and overhaul 3 predictive tactics are condition based maintenance and repair activities predictive maintenance techniques rely on a measure of performance deterioration to intervene prior to failure and include oil analysis vibration monitoring and thermography 4 proactive tactics are based on a root cause they include design out maintenance design modifications reliability in procurement and warehousing operator driven reliability and operating restrictions designed to eliminate the root cause of problems a tactic is defined by the type of maintenance and repair action to be realized and the criteria for determining when to apply that action unscheduled maintenance work arises as a result of reactive tactics scheduled maintenance comprises preventive predictive and proactive maintenance work see figure 9 9 3 the production plan is formulated based on estimated sales demand and the current state of the productive equipment and infrastructure the production plan drives the asset management plan which specifies availability reliability and capability targets for productive equipment and infrastructure assets these targets drive the selection of maintenance tactics within the infrastructure maintenance plan these choices in turn determine the maintenance workload which dictates the level of resources labor

equipment and tools required in the real world the maintenance budget restricts the extent of these resources the maintenance plan must be adjusted by reviewing the type and frequency of tactics to accommodate the budget selection of maintenance tactics infrastructure assets are constructed to fulfill a useful role or purpose known as the primary function of the asset the purpose can be defined by answering the question what do we want the asset to do for example the primary function of a hoist system might be stated as to lift 5 000 t d of ore from the 300 m level to the surface stockpile however secondary functions often must also be fulfilled these include environmental integrity safety structural integrity control containment comfort and appearance a secondary function of the hoist system is that the skip must decelerate to a creep speed before each station protective functions are a subset of secondary functions and provide protection against environmental damage or risks to health or safety in his book reliability centered maintenance moubray 1997 defines a functional failure as the inability of an asset to fulfil a function to a standard of performance which is acceptable to the user reliability centered maintenance rcm attempts to guide the selection of maintenance tactics by preventing loss of functions that might lead to health safety and environmental risk exposure and preserving functions necessary for operating capability in the rcm methodology the following questions are asked in order 1 what are the functions and associated desired standard of performance of the asset in its present operating context 2 in what way can it fail to fulfill its functions functional failure 3 what causes each functional failure failure modes 4 what happens when each failure occurs failure effects 5 in what way does each failure matter failure consequence 6 what should be done to predict or prevent each failure proactive tasks 7 what should be done if a suitable proactive task cannot be found figure 9 9 4 shows a simplified rcm decision tree for selecting maintenance tactics for each failure mode being evaluated maintenance tactics are defined by beginning the logic at the top left corner of the decision tree it can be seen that maintenance tactics are defined first on the basis of the consequence of the failure and second on the failure type wear out random burn in or early life failures rcm decision trees such as that shown in figure 9 9 4 are extremely useful for defining the type of maintenance activity to apply however they do not help to define the frequency with which these activities should be applied a trade off exists between the frequency with which preventive maintenance is scheduled and the cost of lost production incurred if maintenance is insufficient the result is a high likelihood of breakdown and significant production losses at the other extreme overm

aintaining an asset also results in production losses as figure 9 9 5 shows there exists an optimal frequency with which to schedule preventive maintenance activities determining this optimum however is not a trivial task and will not be dealt with in this chapter readers are referred to jardine and tsang 2006 life cycle costs and maintenance strategies the root causes of reliability problems figure 9 9 6 are not just due to the maintenance process the way infrastructure assets are specified and designed the price and quality criteria adopted during the purchase process the way certain assets are stored e g shafts of electric motors must be regularly rotated to prevent flattening of ball and roller bearings the way in which installation and commissioning are controlled and the way equipment is operated all contribute to potential failures during operation world class maintenance organizations use root cause analysis techniques to pinpoint the potential causes of failures they then design specification purchasing warehouse and operating procedures aimed at reducing the incidence of failure during operation maintenance activities that involve design modifications are known as design out maintenance synchronizing the maintenance plan with the production plan it is important to synchronize the mine infrastructure maintenance schedule to that of the mine production plan and the production equipment maintenance schedules key to this is the implementation of a process to determine maintenance and repair priorities such processes are usually dependent on the evaluation of the effects and consequences of failure modes one way to determine the criticality of each failure mode is to quantify the expected frequency and impact of the failure and determine whether during normal operating conditions the failure will be evident to an operator quality standard qs 9000 guidelines assign a rating using an integer scale of 1 to 10 to the frequency severity and detectability of each failure mode stamatis 1996 the severity rating needs to consider safety environmental and economic impacts a risk priority number rpn can then be calculated for each failure mode by multiplying the three assigned ratings grouping of the resulting rpn values allows low medium and high priority maintenance and repair tasks to be determined this in turn helps in scheduling high priority tasks have greater reason to interrupt production for immediate attention medium priority tasks can be grouped and completed during the next scheduled preventive maintenance whereas noncritical tasks can often be deferred until the next overhaul window maintenance performance measurement the cost of mine maintenance and its influence on the effectiveness of the total system can be significant mine managers need to know how outputs from investments in the maintenance of infrastructure will contribute to business goals without any formal measures of perform

ance it is difficult to plan control and improve the main purpose of performance measurement is to determine whether systems and organizations are performing as they should this helps determine resource allocation and subsequent control of outcomes one way to compare outcome measures with performance targets is to benchmark performance with competitors maintenance performance indicator mpi is the term used to describe an indicator that is a product of several metrics and is used to measure maintenance wireman 1998 parida and kumar 2006 mining companies use many different forms and types of mpis to measure the performance of maintenance processes mpis show the value of the contribution of maintenance process toward the ultimate objective of the company as a whole mine infrastructure examples the following discussion deals with specific applications of mine infrastructure maintenance related to the provision of safe access to the ore body via shafts and roadways in underground mines it also addresses the maintenance of electrical distribution and dewatering systems in underground and surface mines mine hoisting systems access to ore reserves in underground mines is achieved either by declines or by shafts the economic cutoff depth for decline haulage depends on a multitude of factors including production rate ore grades metallurgical recovery factors truck capacity and haulage speeds deeper underground mines are serviced via shaft hoisting systems apart from providing access to the mine s ore body the shaft also serves as an opening for mine ventilation and a conduit for mine services such as water and compressed air systems shaft availability is invariably at a premium as downtime required to inspect maintain and repair shafts directly translates to an opportunity cost of lost production engineers charged with shaft maintenance are tasked with achieving an appropriate balance between downtime costs and shaft integrity this section describes the fundamental maintenance management requirements of hoisting systems for underground mines major hoist components a hoist system consists of a winder headframe shaft steelwork and guides ropes conveyances and counterweights shafts are typically divided into several compartments figure 9 9 7 shows a typical shaft cross section with cages for personnel and equipment access and skips for the conveyance of ore and waste the winder plant consists of winder drums a braking system drive motors and control system shaft structures this section draws heavily on the work of g j krige 2005 the maintenance of shaft structures is becoming an increasingly important factor in the operation of underground mines because profit margins in deep underground mines are tight the life of old shaft infrastructure is increasingly being extended two key parameters are strength and functionality shaft guides must have sufficient strength to resist the impact forces resulting from the

passage of conveyance and they must be functional in guiding a conveyance without derailment shaft structure deterioration mechanisms engineers charged with the maintenance of hoisting infrastructure are frequently called on to assess the suitability of shaft equipment with various levels of deterioration for safe hoisting thus it is necessary to be able to identify measure and manage the principal deterioration mechanisms these mechanisms are caused by operation of the shaft or by rock movements due to mining or seismic activities deterioration from shaft operation the following deterioration mechanisms are related to the operation of shafts steel corrosion the most common deterioration mechanism in deep shafts is corrosion of steel comprising shaft buntons and guides pipes and pipe support brackets and station or platform structures generalized corrosion affects the entire exposed area of all steel structures and localized corrosion affects specific areas of the structure generalized corrosion results from ambient atmospheric conditions within the shaft including the gaseous content humidity and temperature of air typically shafts with upcast air are more prone to generalized corrosion than shafts with fresh downcast air generalized corrosion uniformly reduces steel thickness and leads to a uniform reduction in the residual strength of steel components localized corrosion results when corrosive chemicals and moisture are trapped in pockets where spillage can accumulate cable trays flat horizontal surfaces or at the ends of buntons as a result of water running down the shaft lining localized corrosion results in the reduction of strength of the steel member at a particular point mechanical damage mechanical damage may be caused by falling objects in the shaft or by collision of shaft conveyances and shaft steelwork minor mechanical damage may also be caused by spillage but it seldom causes significant loss of strength or functionality of steelwork major mechanical damage often causes complete loss of functionality without significantly impairing strength fatigue damage fatigue damage of steel shaft structures is caused by repeated loading cycles during the operation of the shaft the loading cycle results from the passage of conveyances within the shaft load magnitude is determined by guide misalignment bunton stiffness hoisting speed and conveyance effective mass fatigue cracking at welded joints is a real possibility usually occurring at or close to connections loss in strength and functionality is similar to that caused by localized corrosion wear wear is a deterioration mechanism usually confined to conveyance guides wear does not compromise strength but it may affect functionality localized wear may be indicative of misalignment of buntons due to rock movement deterioration from movement deterioration mechanisms related to rock movements or seismicity within a mine include those described in the fol

lowing paragraphs vertical strain ongoing mining can progressively reduce the area that has been supporting the weight of overlying rock resulting in vertical compressive strain this vertical strain in the rock can be induced into the shaft guides a compressive strain causes bowing of the guides between bunton levels strain limits should not exceed the closure of permissible gaps left between shaft guides horizontal ride some shafts are constructed to pass through the ore body this is typical of reef mining as practiced in south africa redistribution of stresses following orebody extraction can result in horizontal dislocation of the shaft above and below the reef it may lead to severe distortion of the buntons installed between the hanging wall and footwall of the ore body vertical closure and squeezing changes in rock stress caused by mining can produce vertical and horizontal displacement of the shaft unless adequate provision has been made for vertical closure during the design and construction of the shaft shaft steelwork can become severely distorted redistribution of horizontal stresses as a result of mining activities can cause inward pressure on shaft walls squeezing or distorting the shaft section this leads to cracking or crushing of concrete in the shaft lining buckling of shaft steelwork and piping and misalignment of guides changes in horizontal stress state have also reduced clearance between shaft conveyances and shaft steelwork or walls increasing the likelihood of impact of the conveyance with steelwork shaft structure maintenance a three step strategy is proposed for defining the maintenance strategy for deep shaft structures 1 define limits and requirements using analytical techniques this means that the misalignment and deflection of deep shaft structures must not exceed the specified maximum analytical techniques based on well established shaft design procedures e g sans 10208 3 2001 can be used to establish acceptable limits to deterioration 2 implement measurement and inspection procedures information must be captured recorded and reported on a regular basis by mine personnel working in the shaft who know the shaft well the deterioration condition should be described within a limited number of categories there should be enough categories to enable meaningful trending while still allowing memorization and simple categorization table 9 9 1 lists six shaft categories developed by anglo american corporation krige 2005 color coding can be used as an effective reporting means with green indicating structural members classified as category 0 or 1 condition yellow categories 2 and 3 and red categories 4 and 5 3 monitor trends and schedule maintenance most shaft deterioration takes place slowly so changes may not be noticed it is important to track deterioration over time table 9 9 2 gradual movements of bolts in slotted holes and gaps between structural members may be observed

and quite suddenly further ground movement can result in buckling of buntons corrosion can progressively reduce the stiffness of conveyance guiding systems over many years again quite suddenly with no specifically observed changes conveyances may start to derail because reduced stiffness has led to dynamic displacement of the conveyance exceeding the upper limit condition monitoring of guides hecker 2005 provides a useful summary of predictive maintenance techniques used to assess guide alignment these methods include the following plumb lines the most common method of aligning shaft steelwork is based on vertically suspended plumb lines often the distances to be measured are large causing plumb lines to sway because of air movement in the shaft to overcome this steady state brackets can be installed to hold the lines still at the points in the shaft and the plumb bobs can be suspended inside oil pots because lines have to be suspended outside of compartments distances often have to be measured at awkward angles both factors can lead to measurement errors laser beams calver 1982 described a method of mounting a laser onto a guide a target is placed on the same guide at a distance away from the laser this distance is chosen such that refraction caused by water in the air and temperature gradients is minimized the target is then moved progressively closer to the laser and fixed to the guide at intermediate positions at each position the target is adjusted so that the laser beam coincides with the center of the target allowing a deflection profile of the guide to be established inertial platform inertial platforms were first developed in belgium and south africa such a system consists of a platform suspended from a conveyance proximity transducers on the platform measure the distance between the platform and the guides accelerometers and sometimes gyroscopes measure platform motion double integration of the accelerometer signals can be used to calculate the path that the platform follows down the shaft the deflection profile of each guide can be calculated by adding the distance between the platform and the guide to the amount by which the platform deviates from the vertical in each direction moving beam systems moving beam systems consist of beams running along the guide rails guide curvature can be measured by recording the distance between the center of the beam and the guide face or by measuring the inclination of the beam the guide shape can then be calculated from the successive curvature readings obtained hecker 2005 hoist ropes wire hoisting ropes are constructed of an assembly of steel wires that operate at high stress levels and are almost invariably subjected to fluctuating rope loads a significant source of stress fluctuation is the repeated bending and straightening of ropes as they run over sheaves greenway 2005 provides the following list of factors affecting the life of winding r

opes manufacturing standards and quality rope design and selection for envisaged duty the provision and selection of a satisfactory operating environment the control of loading of in service ropes rope safety is affected by the following factors greenway 2005 control and limitation of manufacturing defects effective assessment of rope condition to identify the optimal moment to discard the rope detection of abnormal rope damage control and limitation of severe peak rope loads chaplin 2005 lists the following factors that contribute to degradation and fatigue of hoisting ropes tensile fatigue tensile fatigue results from the fluctuation of axial tensile loading changes in the attached mass and acceleration are the primary sources of axial load fluctuation for this type of fatigue dominant parameters are the tensile load range mean tensile load rope construction and wire grade environment including lack of effective lubricant or exposure to corrosion and manufacturing quality bending of sheaves fatigue this form of fatigue involves repeated bending while under constant tensile load the primary sources of stress fluctuation in this mechanism are the local changes in wire curvature as the rope adjusts to the radius of the sheave or the drum restriction of the source of fatigue stresses to change in wire curvature requires that individual wires can slide with respect to one another any constraint to this freedom or ineffective lubrication or internal corrosion will impair fatigue endurance free bending fatigue free bending fatigue involves fluctuating bending deformation that does not involve contact with another body and that is typically excited by system dynamics in fixed rope applications this type of bending often takes place adjacent to a termination torsion fatigue a consequence of the geometry of many ropes is that they generate a torque in response to a tensile load when the ends are constrained some rope constructions are designed to minimize this tendency to rotate but these can have other disadvantages such as not being as robust under certain applications of wire ropes such as moorings of offshore systems torsion fatigue can be a dominant mode of failure combined modes in practice life of a hoisting rope is dictated by a combination of fatigue modes usually tensile and bending of sheaves fatigue briem 2005 provides a useful method for estimating the fatigue life of wire hoisting ropes on drum winders as defined by a limiting number of single bending cycles hoist rope inspection procedures to ensure safe operation mining companies are required to inspect hoist ropes visual inspections are performed daily and electromagnetic induction tests are performed every three to four months during visual inspection rope speed is reduced so that an inspector can look for visible signs of rope defects this typically results in the loss of about half an hour per day of shaft time electroma

gnetic em analysis of hoist ropes uses a data capture system that wraps around the head of a rope allowing it unhindered passage the em head induces eddy currents within the rope and a signal or trace is returned that is proportional to rope section integrity and thickness local faults are generally detected as local spikes on the em trace and loss of metallic area shows up as a sustained dip in the trace young and delaney 2005 describe the development of an automated hoist rope inspection system in which an em detection head was integrated with a vision system and hoist drum encoders pattern recognition software linked to the camera data picks up visible signs of deterioration digital signal processing of the em traces is as outlined previously underground roadway maintenance haulage roads in any mine are an integral part of the production system and make a significant contribution to the mine productivity safety and economics a haulage road can be broadly classified in one of three categories 1 permanent haul road 2 service haul road 3 temporary haul road all haulage roads need a carefully planned maintenance program otherwise they can turn into a major production bottleneck underground roads provide access from the shaft or decline and the ore body good roads are essential to moving personnel and materials around an underground mine poor roads result in maintenance downtime which restricts access to parts of the ore body the costs include lost production damage to mobile equipment resulting in increased tire and vehicle repair costs and lack of vehicle availability and roadrelated accidents resulting in injury and compensation claims degradation mechanisms the following text draws heavily on a paper by logan and seedsman 1995 road defects are the result of interactions of the excavation process pavement materials traffic environmental conditions and road construction causes can be linked to poor floor horizon control lack of drainage poor compaction or the use of inappropriate material to carry high axle loads water plays a critical role in the degradation of underground roads only small quantities of water are required to deteriorate pavements key degradation mechanisms include the following potholes which form when induced water pressures cause layer separation areas where poor drainage has led to water retention are particularly susceptible to potholes ruts which are deformations in wheel paths in parallel directions this is a characteristic of soft clay floors shoving whereby road material is moved sideways by cornering braking or sliding wheel forces slippery surfaces caused by presence of clay materials or sediments on the surface of the roadways maintenance of underground roadways maintaining underground roadway surfaces has three main objectives 1 to provide a good riding surface 2 to minimize safety hazards for vehicular traffic 3 to provide a free draining surface

as a road deteriorates several maintenance procedures of moderate cost can be used to prolong its life these include grading compaction drainage maintenance and resurfacing grading profiles logan and seedsman 1995 regard grading as the single most important function in maintaining an underground road network regular grading to maintain crossfalls eliminate surface defects and restore drainage profiles reduces the effects of surface water lack of adequate crossfalls is one of the principal problems associated with roads crossfalls should normally be in the range of 1 25 to 1 17 compaction after grading compaction of pavement materials can assist pavement performance and minimize maintenance intervals by increasing the strength of the pavement and its resistance to water drainage these maintenance tasks for drainage systems are essential checking that flow from drippers is collected and directed away from the pavement cleaning roadway drains of debris to ensure free flow of water away from the pavement regularly inspecting and maintaining roadway pumps to ensure effective operation and clear the inlet of debris regularly cleaning settling pumps to ensure effective pump operation and prevent overflow checking and flushing drain lines to prevent sediment buildup and reduce duty on pumps locating and addressing new sources of water resurfacing pavement resurfacing may be required as a result of degradation of the road aggregate incorrect selection of pavement material traffic abrasion shoving and mixing of the road base with weaker material or scouring and erosion due to water flow if resurfacing is required the weaker material should be removed and new material should be added and mixed with existing strong materials the pavement should then be shaped with a grader and compacted and drainage should be reestablished electrical power distribution systems this section describes the essential features of electrical power systems used in surface and underground mines and their maintenance management because mining operations are highly mechanized mines and processing plants consume large amounts of electricity the mining engineer is expected to be aware of the utility applications limitations and risks involved in the use of electrical power as well as the maintenance of electrical infrastructure alternating current ac is the standard power supply although direct current dc is used in certain specific applications such as motors requiring speed control the transmission and distribution of ac power requires voltage variation using a network of transformers the main transformer onsite receives grid power to the mine site alternatively diesel electric ac power generators can be used in areas where the electrical grid power is inaccessible mining operations require mechanical power for most work and mechanical power is often facilitated by the use of electrical motors to drive various accessories fo

r example material handling equipment ventilation fans and hydraulic equipment such as rock drills therefore mining engineers need to have an understanding of the maintenance aspects of motors and motor starters transformers and distribution cables that power mining equipment to a very large extent predictive maintenance methods are replacing the traditional usage based maintenance in the management of electrical infrastructure in mines stages of power distribution and power factor most mines are large consumers of electrical power if the power is supplied by the electrical mains grid where the transmission voltage is 33 kv or more the voltage is usually stepped down to 11 kv using a main transformer located on site alternatively if the power is supplied by a diesel generator the voltage may need to be stepped up to 11 kv power is then distributed via a network of feeder cables to substations located on the surface facilities and in underground locations the substation transformers modify the voltage as required by the applications in surface mines the main consumer is electrically driven mining equipment such as draglines and shovels in underground mines the main consumers are ventilation fans large drilling machines used for mine production and rock reinforcement and dewatering pumps generally a substation transformer supplies power to all the applications in its locality the power factor is one of the significant parameters that should be monitored in the use of electrical power it is defined as the ratio by which the product of voltage and current is multiplied to obtain the true electrical power rizzoni 2007 hence power factor cos apparent power true power where cos is the cosine of the phase angle between the current and voltage vectors the product of v and i is called apparent power and pt v i cos where pt is true power v is voltage and i is current the power factor is affected by the inductive and capacitive components of the electrical infrastructure which includes both the distribution system and the consuming appliances if the power factor is low the current increases to supply true power given in kilowatts increasing the power factor close to unity is significant in any power distribution system to limit the current flow through the circuit this is known as power factor correction in practice most circuits are inductive and as a result cause currents to lag behind the line voltage a circuit with a leading current capacitive circuit is seldom found however these effects do occur in long distance power lines these are the two major causes of low power factor 1 lightly loaded electric motors and transformers this equipment should be designed to run at or near full load 2 fluorescent lighting circuits these lights have to be considered carefully and steps taken to improve their power factor correcting the power factor is part of daily maintenance in a large power consum

er the optimum power factor achievable is about 0 85 safety aspects of electrical power a range of protection devices and methodologies may be applied for the safe use of electrical power to maintain safety it is vital that these devices be properly installed inspected and maintained and that correct practices be followed in their use earth leakage protection earth fault protection is a crucial aspect in the use of electrical power in underground and open pit mines where high voltage electrical cables are frequently used to power mining equipment the main purpose of earth fault protection is to safeguard personnel and electrical apparatuses unless properly controlled the occurrence of an earth fault can be hazardous at a mine because it may cause voltages from machine frame to earth which are dangerous to personnel or electric arcing underground which may initiate an explosion or fire the most common apparatus faults in mines occur in power cables as they are susceptible to damage caused by heavy equipment this is particularly true of flexible trailing cables that supply power to mobile mining machines they are laid over ground or close to ground level and it is almost impossible to prevent their damage by road traffic and during relocation of the cables cable construction is such as to provide every phase conductor with an individual conductor screen so that crushing would expose a single phase creating an earth fault current a protective device such as an earth leakage relay would then isolate the cable and contain the sparking within the cable before the occurrence of a heavy short circuit current due to a phase to phase fault coordination among protective units is introduced to allow the unit closest to the fault to isolate the faulty circuit without causing the healthy part of the system to be deenergized effect of current exposure to human body though desirable it is almost impractical to provide automatic protection against electrocution as a result of direct contact with a live conductor particularly where the electrical reticulation is exposed to a humid or damp atmosphere to appreciate this it will be necessary to study the effects of current values on human beings table 9 9 3 as the table indicates passage of current as low as 20 ma through the human body can cause loss of muscular control to the extent that an individual cannot disengage from the live conductor and a current in excess of 50 ma is sufficient to produce a critical heart condition from which there is little or no chance of recovery for effective safeguard against electrocution it would be necessary to introduce earth leakage protection designed to operate with a fault current below 20 ma which in most cases would be impractical methods of earth fault protection two main methods are used for earth fault protection they are earth leakage protection and earth continuity protection the earth leakage protection devices are activated b

y any unbalanced current of any phase of a three phase circuit caused by an earth leakage the leakage current should not exceed 1 or 2 a for most applications and it is limited to 30 ma for portable apparatuses operated by personnel mines safety and inspection regulations 1995 the principal purpose of earth continuity protection is to ensure a continuity of earth conductors throughout the length of the supply cable and associated connectors all trailing cables have either a separate central conductor called a pilot wire or they use a pilot wireless monitor through the cable conductors the pilot wire pilot wireless systems are connected to a solid state frequency controlled system to ensure the continuity of the ground conductor in case of damage if the signal level becomes too low indicating excessive resistance in the pilot wire pilot wireless system or the frequency is outside tolerance the monitor indicates a fault condition and opens i e trips the control relay most mine regulations specify that automatic protective devices must be tested periodically for proper operation mulvaney 2008 other protection devices that ensure safe power usage are surge diverters which protect the circuit from overload surges such as those due to lightning circuit breakers which respond to overloads and quench the resulting arc in a way that will not affect other parts of the system fuses which open the circuit when excessive current flows through it and manually operated isolators and switches maintenance of major components used in electrical power reticulation the major components that require maintenance are the transformers switchgear and protective equipment the protective equipment is also used with ventilation fans pump motors electrically powered mining machines such as rock drills and trailing cables usage based maintenance is commonly practiced in many mines however predictive maintenance based on condition monitoring improves reliability and should be implemented wherever possible the following points relevant to the maintenance management of major components are suggested transformers use air or oil as a medium for cooling and insulation regular monitoring of the condition of oil is useful as a predictive tool to determine the performance of the transformer oil analysis gives information about the integrity of insulation of the transformer windings dissolved gases resulting from any arcing within the windings water contamination and the degree to which the oil itself has deteriorated arcing may occur as a result of breaking down of insulation properties in oil a thorough visual examination for oil leaks including temperature measurement and a test of relief valve operation should be carried out periodically as trailing cables are subjected to frequent movement in a harsh mining environment they accumulate damage over time the insulation resistance is one indicator of the accumulated damage hipot o

r megger testing are popular insulation test methods practiced by many companies however both methods damage the cable and reduce its operational life it is not recommended to conduct destructive testing of cable insulation ieee 400 2001 2002 states that partial discharge testing is nondestructive and more accurately gauges insulation integrity this information is useful for timely replacement of the cable trailing cables should be equipped with both earth leakage relays and earth continuity relays mines have typical apparatuses such as dewatering pumps and ventilation fans suppliers of this equipment usually provide maintenance information however it is the responsibility of the mine s personnel to perform the routine maintenance dewatering pumps must be equipped with devices such as flow sensing relays reservoir water level sensors and position indicators of inlet and outlet valves to make sure that the pump does not engage unless there is adequate water the proper functioning of these devices should be checked periodically portable dewatering pumps are not generally equipped with all the flow sensing devices however they are usually fitted with current sensing devices that stop the pump if there is a large variation of the load such as that caused by loss of water also required are regular lubrication of motor bearings and switching contact maintenance of motor starters primary ventilation fans are heavy electromechanical machines the bearings on which the motor shaft is mounted are subjected to wear resulting in increased vibration and heating a periodic measurement of the bearing temperature and vibration monitoring of the fan reveals the condition of the bearings and the dynamics of the fan rotation allowing prior action to be taken before a failure occurs rock drills are subjected to heavy vibration therefore in addition to periodic checking of the trailing cable the electric panel should be checked for loose contacts motor starters should be selected considering the applications for example variable frequency drive starters help to regulate the motor speed and they can be very costeffective for use with primary and secondary ventilation fans where constant full speed operation is not required also these starters work well with automatic and remote control systems other types of starters commonly used are soft starters having electronic control of starting voltage star delta starters and direct on line dol starters the dol starters are suitable only for low power applications as the starting current of the motor can be as much as seven times the full load current because of the presence of moving parts and the heavy current experienced by starters wear is usually high and the frequency of inspection and maintenance should be adjusted as required mine regulations usually specify that earth leakage relays need to be checked for proper operation at frequent intervals e g monthly als

o power cables and earth grounding must be checked periodically the resources needed for maintaining the electrical infrastructure depends on the extent and complexity of the electrical equipment most mines require a lead hand who can also act as a supervisor and other electricians at least one electrician shoud be required to work during each shift specialized contractors may be needed for specialized or statutory work such as that dealing with high voltage also required are an electrical maintenance shop and an inventory of consumables and test equipment a reliability focused maintenance plan should be developed to keep the mine electrical system in good working order necessary precautions must be taken to minimize the risk of earth fault as mines use flexible power cables and associated gear for power distribution mine regulations stipulate the periodic testing of earthing systems protective devices cables and other electrical equipment and use of a logbook is required to maintain all testing and examination records during maintenance of mining equipment personal danger tags are used to communicate with equipment users that their equipment is being serviced dewatering systems open pit mines vary in size and depth large pits can be several kilometers in length and width and up to a kilometer deep in most instances the depth is greater than that of the natural water table a variety of methods are used to remove water ingress some mines remove water continuously via bore pumps located around the pit others pump away water collected in a sump at the bottom of the pit regardless of the method employed it is necessary to use one or more pumps that can remove the peak water ingress that may occur during the rainy season this will keep the drawdown level i e depressed water table level below the pit depth dewatering of pits situated close to lakes or nearby abandoned mines can be challenging if seepage occurs selection of pumps used for dewatering many types of pumps are used to remove water from mines the factors that determine the type of pump are flow rate pressure or elevation density of water and suction head that should not exceed a given limit centrifugal pumps are adequate for most dewatering applications and are commonly used for lifting water up to about 300 m 1 000 ft multistage pumps can be used for removing water at greater depths munson et al 2006 in underground mines positive displacement rotary pumps are popular because of their self priming capability plunger and diaphragm pumps are also used the design of centrifugal pumps is a highly developed field actual pump characteristics are experimentally determined through tests and supplied by the pump manufacturers typically they include a graphical relationship between the total head and the discharge as well as identification of the zone where the pump efficiency is high for a given head and a discharge a suitable pump can be selected

considering its efficiency as well furthermore pump characteristics also include what is known as net positive suction head this is useful to determine the maximum suction height of the pump while allowing for pressure losses in the pipe head loss in pipes head loss in piping should be taken into account in determining the overall pressure head required for pumping this consists of the pipe friction loss and the shock loss when the fluid passes through sharp bends and turns which should be eliminated or minimized during construction and maintenance pipe manufacturers usually provide the friction losses piping handbooks give the shock loss factors applicable to sharp changes in the piping geometry crowe et al 2008 alternatively losses due to bends and other geometric changes of a pipe can be expressed as an equivalent increase in the length of the pipe subjected to frictional resistance often it is more convenient to include the effect of geometric changes as an added length which is provided by the pipe manufacturers planning and managing surface mine dewatering for mining to be carried out without the hindrance of groundwater ingress many managers seek to reduce the level of the water table below the depth of the mining pit the usual strategy for doing so is to pump from several bore water pumps before constructing the surface mine and during mine operation alternatively the water collected in sumps at the pit bottom is removed in some mining operations the following considerations can be useful during planning and operation of the dewatering system the estimate of water ingress should be based on a hydrological study the existence of nearby abandoned mines or large reservoirs such as lakes must be considered previous experience with groundwater in bores or drill holes in and around the location can also be useful as can construction of test bores place of discharge should be decided considering the geology if the ground is permeable water must be sent to a reservoir far distant from the mine electric submersible bore pumps which are available in a variety of sizes and capacities can be used bore pumps are usually multistage centrifugal pumps although they are quite reliable they can be easily damaged by letting them run without water and or under cavitating conditions hence flow sensing switches should be incorporated to ensure that pumps stop automatically when adequate water is unavailable they may be reenergized after a preset time lapse pump manufacturers provide automatic pump controllers and alarm transmitters in many sites the yield of water increases substantially for weeks or months and then gradually lessens pumping should continue until the drawdown is below the pit bottom the drawdown can be measured by inspecting the level of water in drill holes or well bores in some cases dewatering is done using a sump located inside the mining pit centrifugal pumps with horizontalor vertic

al axial configuration can be used as appropriate however they should be located near the sump so suction head restrictions are satisfied pumps driven by diesel engines are commonly used at some locations inside a surface mine if electrical power supply is unavailable if the depth of the mine is great and or the delivery distance is large a transfer tank may be required on the ground level adjacent to the pit for temporary storage of water silt may be removed by sending it through a precipitation tank in this case secondary pumps are needed for delivery of water to the final destination pumps configured to operate in parallel increase the flow rate without increasing the total head those configured to operate in series increase the total head without increasing the flow rate the main considerations in selecting a pump for dewatering are capability reliability portability and wear resistance both reliability and wear resistance are affected by operational conditions the correct grade of polyethylene pipe one that can withstand the applied pressure should be used the size of the pipe should be determined considering the flow rate a velocity of 3 m s 9 8 ft s is an upper limit considering the frictional losses in a pipeline a minimum velocity of about 1 m s 3 2 ft s is required to prevent settling of solid matter inside piping the settling velocity depends on the maximum size of the solid particles carried by water to minimize damage to the piping and to reduce maintenance all piping must be securely fastened this is necessary because pipes tend to move about when subjected to internal pressure and in particular when dynamic transient pressures occur if the delivery pipe passes through steep elevations one should be aware of the possible occurrence of large negative pressure in the falling side of the pipeline vacuum relief valves may be required to prevent pipe collapse similar conditions may occur when the pump is suddenly stopped where the water is delivered through a long pipeline the life of a pump particularly if it is used for pumping saline or corrosive waters is affected by the material it is made of the expected mine life should be considered when pump material is being selected even a long lasting and expensive pump if it is operated under abrasive conditions may require regular replacement of the impeller or volute chamber some important considerations in the design and maintenance of sumps and transfer tanks are to provide adequate excess capacity to cater for pump downtime install trash screens and grit traps ahead of the pump intake and facilitate the regular cleaning of deposited material in screens and grit traps a vacuum gauge installed in the suction side of a pump gives useful information about its performance an unusually high suction pressure may indicate a blocked suction pipe and or cavitation occurring whereas a low value may indicate that air has leaked into the su

ction pipe or that the pump has not been primed similarly an unusually low reading in a pressure gauge installed in the delivery side may indicate no flow excessive air in the water and so on an increase in the delivery pressure indicates a blockage or a closed valve in the delivery pipe excessive vibration in a pump may be an indication of an unbalanced or worn out impeller worn bearings or a damaged shaft kuruppu 2008 maintenance management of dewatering infrastructure the maintenance management strategy should be designed to minimize the total dewatering cost over the planned life of the pit this may include adding more resources such as equipment for performance monitoring replacement of parts routine cleaning and inspections and reengineering of the existing infrastructure if the current system is not reliable an optimum level of maintenance is that which corresponds to the lowest total dewatering cost table 9 9 4 gives a list of maintenance strategies commonly adopted by maintenance personnel table 9 9 5 shows the factors that should be considered when formulating a maintenance strategy reactive maintenance which would be required in case of equipment failure can be minimized by adopting these strategies adequate resources must be available to meet the requirements of maintenance the resources usually required are skilled personnel such as team leaders plumbers and fitters parts required for pumps and prime movers e g diesel engines accessories such as piping and pipe fixtures and material handling equipment in conclusion dewatering of pits requires proper consideration of the rate of water ingress and the total pressure head needed for suction and delivery of water the total head depends on suction height delivery height and friction loss in the piping once the pumping system is operational the reliability of the pump can be adversely affected by air entrapment due to low water level and by abrasive material such as sand mixed with water the latter causes rapid wear in the impeller and the housing other problems are clogging in the suction and delivery pipes and the occurrence of transient pressures in the delivery pipe resulting from sudden interruption to pumping to minimize damage to pumps and piping and the disruption of dewatering these issues require proper planning monitoring and control cutoff grade and scheduling optimization heuristic cutoff grade optimization algorithms cutoff grade is traditionally defined as the grade that is normally used to discriminate between ore and waste within a given ore body this definition can be extended to mean the grade that is used to differentiate various ore types for different metallurgical processing options although the definition of cutoff grade is very precise the choice of a cutoff grade policy to be used during an exploitation of a deposit is not use of simply calculated breakeven cutoff grades during the production would in most instance

s lead to suboptimum exploitation of the resource exploitation of a deposit in such a way that the maximum net present value npv is realized at the end of the mine life has been an accepted objective of mining companies the npv to be realized from an operation is dependent on interrelated variables such as mining and milling capacities sequence of extraction and cutoff grades these interdependent variables interact in a complex manner in defining the npv of a project the sequence of extraction is dependent on the rates of production the grade distribution of the deposit and the cutoff grades cutoff grades cannot be determined without knowing the extraction sequences and capacities of the mining system the determination of capacities is directly related to the cutoff grades and extraction sequences mine planning is a process that defines sets of values for each of these variables during life of the project the biggest challenge during the mine planning is to define the capacities of the mining system that are in perfect harmony with the grade distributions of the deposit through the planned extraction sequence and cutoff grade policy for a given set of capacities the economic costs associated with the capacities within the mining system the pit extraction sequence and the prices there is a unique cutoff grade policy that maximizes the npv of the project the determination of these cutoff grades during the life of the mine is the subject of this section traditional cutoff grades in open pit mining consider a hypothetical case study where an epithermal gold deposit would be mined by an open pit table 9 10 3 gives the grade distribution of the material within the ultimate pit limits of this deposit table 9 10 4 gives the assumed capacities and accepted costs to mine this deposit at a 2 720 t d 3 000 st d milling rate traditionally in open pit mining a cutoff grade is used to determine if a block of material free standing i e without any overlying waste should be mined or not and another cutoff grade is used to determine whether or not it should be milled or taken to the waste dump the first cutoff grade is generally referred to as the ultimate pit cutoff grade and it is defined as the breakeven grade that equates cost of mining milling and refining to the value of the block in terms of recovered metal and the selling price in the calculation of the milling cutoff grade no mining cost is included because this cutoff is basically applied to those blocks that are already selected for mining by the first cutoff to get to the higher grade ore blocks and those blocks that the cost of mining will be incurred regardless of the action to be taken with respect to milling it notice that the depreciation costs the general and administrative g a costs and the opportunity costs are not included in the cutoff grades given in the traditional cutoff grades the basic assumption is that all of these costs including fix

ed costs defined as g a will be paid by the material whose grade is much higher than the established cutoff grades the first cutoff grade is used to ensure that no material unless they are in the way of other high grade blocks is taken out of the ground unless all of the direct costs associated with gaining the metal can be recovered this assurance is automatically built into the ultimate pit limit determination algorithms such as lerchs grossmann and the moving cone the second cutoff grade is used to ensure that any material that provides positive contribution beyond the direct milling refining and marketing costs will be milled the general characteristics of the traditional cutoff grades are established to satisfy the objective of maximizing the undiscounted profits from a given mining operation are constant unless the commodity price and the costs change during the life of mine and do not consider the grade distribution of the deposit heuristic cutoff grade optimization techniques mining the deposit under consideration with a traditional milling cutoff grade of 1 2 g t 0 035 oz st at 95 mt 1 05 million st milling capacacity as long as the operator mines and processes the blocks of material with grades greater than or equal to the static cutoff grades without considering deposit characteristics only the undiscounted profits will be maximized the maximization of discounted profits versus npvs are two different things when the objective is to maximize the npvs the maximization of profits without the time value of money amounts to optimization without the capacity constraints of the mining system and thus when viewed within the framework of constrained npv optimization always yields suboptimal npvs realizing the fact that mines that are planned with traditional cutoff grades would not result in maximum npvs many approaches have been suggested to modify the traditional cutoff grade policies such that the npvs from a given operation are improved the concept of using cutoff grades higher than breakeven grades during the early years of an operation for a faster recovery of capital investments and using breakeven grades during the later stages of the mine has been practiced in the industry for heuristic npv optimizations creasing mining costs declining average ore grades environmental considerations and improved health and safety awareness are some of the main challenges facing the mining industry today caccetta and hill 1999 these challenges emphasize the need for optimization of mining especially when it concerns large scale mining associated with open pit operations the underlying message expressed in this chapter is that an open pit mine is an increasingly complex and interdependent system that can only be optimized by careful coordination management and harmonization of its individual elements definition of open pit mining open pit mining can be defined as the process of excavating any near surface ore

deposit by means of an excavation or cut made at the surface using one or more horizontal benches to extract the ore while dumping overburden and tailings at a dedicated disposal site outside the final pit boundary open pit mining is used for the extraction of both metallic and nonmetallic ores application of this mining method in coal is less common open pit mining is considered different from quarrying in that it selectively extracts ore rather than an aggregate or a dimensional stone product the main difference between strip mining commonly used in the mining of shallow bedded deposits and open pit mining lies in the overburden disposal in strip mining overburden is dumped directly onto mined out panels rather than outside the final pit boundary as is typical of open pit mining production tonnages for open pits range from fewer than 15 000 t metric tons yr in small iron ore operations to more than 360 mt yr in large porphyry copper operations such as escondida in chile as of 2008 there are approximately 2 500 industrial scale open pit metal mines in the world which is approximately 52 of all industrial scale mining operations iron ore 44 copper 38 and gold 15 together account for 97 of the total open pit excavation volume raw materials group 2008 typical deposits by definition ore bodies mined through open pit mining are located at or near the surface although the geometry of ore bodies varies from pit to pit as a general rule it can be said that open pit mining favors ore bodies that can be mined on a large scale e g extensive ore bodies with low stripping ratios porphyry copper deposits such as chuquicamata and escondida in chile and bingham canyon in the united states are prime examples of such large low grade ore bodies other common ore body shapes include stratabound and stratiform deposits such as western australia s iron ore deposits and the zambian copper belt mineralization diatremes typical of kimberlites jwaneng in botswana and carbonatites palabora in south africa and stockworks such as the kalgoorlie western australia gold deposits open pit geometry the geometry or layout of an open pit operation is discussed in this section the main considerations are on those parts of the excavation that have to accommodate the main equipment and their operations namely the benches haul roads and overburden disposal site two other subjects related to openpit geometry pit expansion and transition to underground mining are also included in the discussion benches benches are possibly the most distinguishing feature of an open pit they are crucial in an operation as they accommodate the active blasting and excavation areas benches can be divided into working benches and inactive benches hustrulid and kuchta 2006 working benches are in the process of being excavated whereas inactive benches are the remnants of working benches left in place to maintain pit slope stability between main

benches catch benches are left in place to prevent cascading material from compromising safety in active areas of an operation figure 10 1 1 shows a simplified geometry of a typical open pit as well as the layout of some of the crucial elements in more detail bench heights typically lie around 15 m the bench width varies according to equipment size and the type of bench working benches should at least be wide enough to accommodate the turning radius of the largest haul truck plus the width of the safety berm caterpillar 2006 however ideally the bench should at least be wide enough to allow the largest haul trucks to clear the excavator under full acceleration depending on the chosen pushback geometry and size of the equipment the width of a working bench can be anywhere from 30 m to several hundred meters the width of catch benches is typically between 3 and 5 m but can vary with overall bench height a small catch berm 1 to 1 5 m is usually included at the edge of the catch bench to improve its effectiveness at containing bench scale rockfalls constituting one of the busiest areas of an open pit working benches have to accommodate large excavators and dump trucks as well as the muck pile formed after a blast therefore maintaining the quality of a suitable working surface is vital to ensure acceptable safety and productivity levels at an active excavation as discussed under haul roads it is important to balance maintenance requirements against the duration and intensity of traffic this is no less true for benches than it is for haul roads floor maintenance resources such as wearing course also known as road base or road capping labor and road maintenance equipment should be allocated according to the added value they have in the operation as a whole the importance of good floor maintenance on benches is emphasized in research by ingle 1991 showing that up to 70 of tire damage may occur in active loading and dumping areas for this purpose it is important that a well drained and smooth surface free of rocks is maintained dozers or front end loaders can be used to aid the main excavator in maintaining good floor conditions furthermore they can increase main excavator efficiency by reshaping the muck pile to increase bucket fill factors and possibly aid in the selective mining of ore and barren rock for health and safety reasons safety berms also known as safety benches or windrows are constructed along crests of benches in a similar manner to those found next to haul roads the main goal of berms is to stop equipment from backing over the edge of a crest generally a berm with a height equal to the axle height e g at least half of the wheel height of the largest truck entering an area is not only a safe design but commonly required by mine safety regulations haul roads haul roads constitute a key element of an open pit mine providing the main haulage route for ore and overburden from active excavatio

n areas to the pit rim and beyond figure 10 1 1 shows the layout of a typical haul road in light of a trend toward increased gross vehicle mass and haulage distance detrimental effects of inadequate haul road design management and maintenance are becoming increasingly costly thompson and visser 2006 possible effects are decreased truck and tire life loss of productivity poor ride quality and excessive fugitive dust generation all these factors can result in exacerbated vehicle and road maintenance and operating costs furthermore statistics provided by the national institute for occupational safety and health niosh show that in the united states haul roads are responsible for 20 of lost time injuries and 42 of fatalities in surface mines turin et al 2001 lastly haul roads can significantly impact pit angles and stripping ratios depending on the adopted design and geometry as such sound haul road design and management can have a significant positive influence on the safety record profitability and environmental impact of a mine thompson and visser 2006 argue that optimal performance of a haul road network can only be achieved through an integrated approach incorporating 1 geometric 2 structural and 3 functional design as well as 4 the adoption of an optimal management and maintenance strategy geometric design covers the basic layout of haul roads based on input criteria such as truck types traffic intensity design life of the road available construction materials and costs the next step structural design goes into more detail determining factors such as required materials for road construction material based on the projected design life and traffic intensity the goal here is to ensure the haul road can accommodate the imposed loads without excessive construction or maintenance costs functional design is mainly concerned with providing a safe vehicle friendly ride at the best economic performance wearing course material selection and performance is crucial during this stage as it is the controlling factor for rolling resistance fugitive dust generation ride quality and surface deterioration rates the last step adoption of an optimal management and maintenance strategy involves developing the most cost effective approach to maintaining the functionality of the haul road this subject is covered in more detail later in the maintenance and management subsection for a more detailed discussion of design and layout of haul roads readers are referred to chapter 10 6 of this handbook general design and operational aspects of haul roads depending on the location and use haul roads are generally around 3 3 5 and 3 5 4 times wider than the largest truck size on two way straights and in two way bends respectively effectively this places the width of most two way haul roads between 20 and 35 m and up to 40 m on bends for one way haul roads a width of 2 2 5 times that of the largest

truck size is generally enough recommended grades lie between 1 and 8 and 1 and 10 10 12 5 but higher grades are possible when trolley assist haulage is used it is important to keep the grade as constant as possible to make truck operation easier and more efficient where speeds exceed 15 km h corners can be superelevated although superelevation should not exceed 1 and 10 or 10 caterpillar 2006 for better drainage on flat sections a cross slope of 2 with loaded trucks on the upper part should be considered on grades minimum cross slope is required for safety reasons angles between roads on intersections should be 90 where possible lastly on two way sections of haul roads a center berm can be constructed there is some debate about the effectiveness of such berms some mines use them others consider them to be center obstacles without any added value that can cause tire degradation before a shift starts operators have to perform a basic vehicle check testing vital systems such as the brakes traffic rules on haul roads vary depending on the operation for example speed limits for haul roads range from 5 to 40 km h large loaded trucks in an uphill haul may not be able to achieve the maximum speed for the rest of a mine site i e workshops stockyards crushers etc speed limits generally range from 10 to 20 km h in light of safety considerations trucks traveling in the same direction are normally not allowed to pass and in most cases passing is also prohibited for light vehicles in most other aspects traffic rules on site closely resemble those of public roads dust haul road dust can have a considerable environmental impact increase maintenance and operations costs and be a serious safety hazard both in the short term by reducing operator visibility and through long term exposure which may cause damage to the respiratory system the main controlling factors in haul road dust are wind speed at the road surface traffic volumes and speed on the haul road particle size distribution of the wearing course material construction characteristics of the wearing course material and meteorological conditions at the mine site thompson and visser 2000 operator exposure can be decreased significantly by fitting cabs with filtration equipment airtight seals and air conditioning as well as increasing the following distance between trucks thompson and visser 2000 state that the most common dust suppression measures include the application of a suitable wearing course material reduction of haulage speeds regular application of water or chemical suppressants and sound haul road maintenance the selection and application of a suitable wearing course combined with regular application of water and chemical suppressants are the most feasible and effective options applying a suitable wearing course should be the preferred control measure as it is a preventive rather than mitigating action and it

has many beneficial effects in other areas of haul road management and maintenance the feasibility of watering and chemical suppressants should be evaluated through a cost benefit analysis watering often seems the cheapest alternative although in light of its short effectiveness and possibly limited water supplies other alternatives may be more feasible thompson and visser 2000 chemical suppressants are more effective at long term dust suppression than water however as production haul roads are highly dynamic in nature chemical suppressants generally do not last very long in these environments as continual watering and grading decreases their effectiveness furthermore they do not mitigate effects of material spillages during haulage and are normally more costly therefore continual watering and grading is in many cases the main type of dust suppression for production haul roads although in some cases a combination of both systems might be the most viable alternative for auxiliary roads that are more permanent in nature dust suppressants are a more viable alternative to continual watering and grading in addition to the measures discussed previously avoiding spillages also plays an important role in fugitive dust suppression and possibly more importantly prolonging tire life chemical suppressants are not effective at suppressing fugitive dust generated from spillages as they are not applied regularly thompson and visser 2000 watering haul roads will mitigate this problem but suffers from the problems discussed in the previous paragraph considering the drawbacks of watering and the effect spillages can have on tire life as discussed in the tire management section later in this chapter avoiding spillages through adequate load placement by the excavator should be preferred over more regular watering maintenance and management rolling resistance is the resistance to motion that a haul truck experiences because of friction the main contributors are wheel load and road conditions and to a lesser extent tire flexing and internal friction minimum rolling resistances of 1 5 radial and dual assemblies to 2 cross ply or singlewheel assemblies are quoted for rear dump trucks estimates of rolling resistance related to tire penetration indicate an increase in rolling resistance of 0 6 cm of tire penetration into the haul road thompson and visser 2003 thompson and visser also report that similar resistances can arise from road surface deflection or flexing as haulage is one of the main cost generators in an open pit mine rolling resistance reduction can lower capital and operating costs considerably some of the main contributors to a high rolling resistance and bad haul road performance are inadequate wearing course construction and application as well as haul road defects such as potholing rutting loose material dust and stones corrugations commonly referred to as washboards surface cracking and insuff

icient drainage if these defects are left unattended they may reduce haul road productivity impede safe vehicle operations and damage equipment five of the main routine maintenance activities for a haul road are 1 dust suppression measures 2 routine surface maintenance 3 clearing material spillages 4 replacing the wearing course material and 5 drainage culvert and shoulder maintenance paige green and heath 1999 thompson and visser 2003 all these measures are aimed at maintaining or improving road quality and will mitigate most haul road defects however because of limited resources and complex maintenance requirements a practical maintenance strategy is more effective at mitigation and prevention of these defects semipermanent and temporary haul roads are commissioned and decommissioned during a mine s life it is vital that the costs of constructing these haul roads are balanced against their design life thompson and visser 2003 underexpenditure of resources on permanent high volume haul roads or over expenditure on short term low volume haul roads can have serious detrimental effects related to premature failure compromised health and safety high maintenance costs for permanent haul roads or an excessive drain on resources for haul roads with a short active life span wearing or surface course material plays a major role in the productivity and maintenance requirements of a haul road and the equipment using it therefore the selection application and maintenance of wearing course materials are paramount to the good functional performance of a haul road during its operational life to determine its influence on overall haul road functionality and road user costs the performance of wearing course materials should be analyzed and benchmarked thompson and visser 2006 visual inspection of haul roads has traditionally been the main method of determining the maintenance needs for haul roads however recent advances in the use of high precision global positioning systems gpss communications and equipment monitoring have led to the development of tools for real time qualitative assessment of haul roads by haul trucks the integration of accelerometers in haul truck mounted road monitoring systems may provide quantitative indicators of haul road quality and as such add a whole new dimension to haul road management thompson and visser 2006 during the scheduling of haul road maintenance it is important to bear in mind traffic intensity preferably expressed as gross vehicle mass function and projected life span of the road as well as its maintenance requirements routine maintenance and grading may seem like best practice but when traffic intensities and maintenance requirements are not taken into account it becomes apparent that this practice may incur excessive maintenance costs on sections of the haul road system with low traffic intensities therefore optimum maintenance intervals should be determin

ed for haul road maintenance activities based on a cost benefit analysis of the relationship between maintenance costs and vehicular costincurring factors related to road maintenance according to thompson and visser 2003 they conclude that balancing the optimum maintenance intervals for haul road maintenance and dust suppression with available resources in conjunction with visual inspection or ideally real time monitoring of haul road performance should form a solid basis for a practical maintenance strategy for all haul roads in a mining complex when this proactive holistic approach to haul road management is implemented significant gains in operating and maintenance costs as well as road construction costs can be achieved two other important elements of a haul road that need maintenance are drainage culverts and safety berms similar in size and purpose to safety berms on working benches safety berms are constructed at the side of a haul road drainage culverts are constructed where climatic and hydrogeological conditions dictate their usefulness they can be located at the pit wall side of the haul road e g where there is a high influx of water or at both sides of the haul road e g for drainage in areas of high precipitation sufficient height of the safety berm and maintaining unobstructed flow in the drainage culverts are essential in ensuring safety on haul roads overburden disposal overburden forms by far the largest volume of material produced by most open pit mines as overburden generally does not generate any revenue handling is kept to a minimum furthermore it can contain sulfides or other substances that are potentially damaging to the environment consequently selection of the most suitable site for the overburden embankment involves a trade off between handling costs related to overburden disposal and the environmental impact of the overburden at a particular site minimizing costs involves selecting an overburden embankment site in close proximity to the mine where the environmental impact is as small as possible preferably this site is as close as possible to the projected final pit limit at the same or a lower elevation as the excavation to minimize upslope haulage costs while maintaining the lowest possible cycle time with these considerations in mind optimization of overburden management at a mine site can have a considerable positive influence on the environmental impact and economic viability of a mine overburden is deposited either top down or bottom up both methods are illustrated in figure 10 1 2 end dumping or top down dumping of overburden involves dumping the material over an advancing face during operation of the dump only limited reworking of material by dozers is required recontouring starts after the end of the dump life in paddock dumping also known as bottom up dumping the layers of overburden are stacked by dumping on top of the dump followed with spreading by bul

ldozers to form relatively thin layers paddock dumping is favored from a geotechnical point of view because it allows for more control over the angle of repose of the dumped material and provides a better homogeneity of the material and ultimately better stability spitz and trudinger 2008 furthermore paddock dumping provides the possibility of concurrent rehabilitation of the overburden embankment and more control over the encapsulation of potentially acidgenerating overburden the lack of homogeneity in top down dumping provides more potential for settlement and creation of zones of different permeability both of which can cause more pronounced erosion and eventually instability moreover the lack of homogeneity in rock size can also encourage oxidation of sulfides and consequently acid mine drainage department of resources energy and tourism australia 2006 paddock dumping does not markedly decrease truck cycle times turin et al 2001 the main advantage of end dumping is that it is significantly cheaper than paddock dumping due to considerably lower rehandling of overburden both during operation and rehabilitation of the dump site however most importantly paddock dumping is far superior in terms of safety because there is less risk of edge failure and a dump truck falling over an edge when backing up this point is illustrated by turin et al 2001 in an analysis of 10 years of lost time injuries and fatalities at overburden embankments in the united states they found that backing up and falling over an edge accounts for 73 of fatalities at dumps three of the main contributing factors to this are edge failure 23 the lack of a berm or barrier 35 and driving through a berm or barrier 31 this not only shows that proper barrier construction is vital but also that dump site stability is an important factor furthermore these statistics highlight that from a safety perspective paddock dumping with its better geotechnical control is the preferred option in order to further increase safety on an overburden embankment it is good practice for haul trucks to approach the dumping face from left to right so the operator can inspect the dump berm and dump surface for any tension cracks the next step is stopping and reversing the haul truck to the dump edge using the berm as a marker rather than a stopping block prior to tipping pit expansion expansion of an open pit mine is done in a series of phases often referred to as pushbacks or cutbacks from a planning standpoint a pushback should be aimed at maximizing the financial return from a mine when planning a pushback this means taking into account not only the grade of a material but also the costs of development mining processing and marketing hall 2009 the exact geometry of a pushback is very site specific and depends on a range of factors including ore body geometry financial goals geotechnical consideration mining equipment production goals and

long term planning pushbacks can be either conventional or sequential mccarter 1992 essentially both methods push back a pit shell the same distance horizontally however a sequential pushback does this through a number of smaller active benches pushed simultaneously at several levels whereas a conventional pushback mines the whole horizontal extent of a pushback level before progressing to the next level different zones of sequential pushbacks are divided by haul roads figure 10 1 3 illustrates the differences between sequential and conventional pushbacks the general pit layout is shown in the top of the figure divided into different pushback zones zone a zone b etc the bottom of the figure illustrates how both methods would mine the same pushback differently the letter in the blocks denotes the zone and the number indicates the mining sequence i e mining commences with block d1 then d2 etc until the last block is mined in a conventional pushback all activity is concentrated on one level as compared to multiple active levels in a sequential pushback this means that sequential pushbacks require more complex planning than conventional pushbacks however developing several areas simultaneously means there is more flexibility during excavation allowing superior control over production planning and blending of ore furthermore as sequential pushbacks contain a number of active benches on the pit slope the working slope angle is lower than the final pit slope angle which does not have these wider active benches resulting in improved slope stability conventional pushbacks on the other hand are less complex to schedule and the larger active area at a given time allows more working faces within a pushback disadvantages include less flexibility in scheduling and blending as well as a greater vulnerability to operational problems presplit blasting is often done at the final reach of a pushback or pit shell by allowing more control over face angle and back break this improves long term stability of the pit face sequential pushbacks are more commonly seen in largescale open pits whereas conventional pushbacks are more common in shallow and small scale operations transition to underground mining in some cases notably with vertically extensive ore bodies it can be profitable to continue mining by underground methods after the final pit limit has been reached in recent years several big open pits such as palabora have commenced underground production with others such as chuquicamata and debswana s jwaneng mine announcing plans to go underground the transition from open pit to underground mining presents a set of unique geotechnical planning and management challenges with regard to management the first challenge is deciding on the feasibility of underground mining most comparison methods between open pit and underground mining rely on establishment of a break even stripping ratio and a comparison of t

he net present value for the next feasible open pit pushback to that for an underground mine after feasibility of underground mining has been proven timing of underground mining is the next issue to be decided there are two major considerations in the timing of the transition first to maintain continuity of the operation it is important that the underground mine can supplement and eventually take over production from the open pit without major permanent changes in tonnages of ore shipped to the mill differences between the open pit and underground ore grade and composition may complicate this issue a production overlap between open pit and underground mining is therefore common to allow for a smooth transition from open pit to underground mining second while a smooth transition requires a production overlap neither of the two operations should compromise the other s safety geotechnical analysis should provide insight into the interaction between the two adjacent operations safety in the surface operations could be jeopardized as a result of crown pillar failure or due to mining subsidenceinduced slope failure e g when a caving method is used on the other hand surface blasting induced vibrations could compromise safety underground siting of the portal is another major consideration in the transition from open pit to underground mining most importantly it is crucial that the stability of the underground mine entrance should not be compromised in any way by surface operations this is as true for a decline portal within an operating pit as it is for a shaft located near a pit wall additionally when a decline portal is sited within the open pit walls surface traffic interactions relating to both excavations should be kept to a minimum this includes not only keeping haulage routes for both operations separated to the highest extent possible but also considering the effects of blasting unit operations in mining unit operations can be defined as those basic steps necessary for the production of payable material from a deposit and the auxiliary operations used to support the production hartman and mutmansky 2002 unit operations in an open pit production cycle include access drilling and blasting excavation practices and haulage methods auxiliary operations and other production related activities include overburden and topsoil removal ancillary operations and mine services and equipment monitoring and maintenance access the first step in the development of a new mining operation or a pushback is gaining access to the area to be mined especially when working in remote areas an appropriately planned and designed access road with sufficient capacity can make a substantial difference in the initial success of a new operation after permanent access to the new mining area has been secured removal of topsoil and overburden can begin in mining overburden refers to all unprofitable material that needs to be excavated to

access an ore deposit including topsoil and overburden topsoil refers to the layer of unconsolidated material at the surface that is suitable for sustaining plant growth because of the unconsolidated nature of topsoil it often requires different excavation techniques depending on climate topography and bedrock geology topsoil can vary from anywhere between centimeters and tens of meters thick overburden refers to the consolidated material underlying the topsoil and generally overlying the ore body if overburden is encapsulated between two layers of ore it can be referred to as interburden topsoil removal after the initial pit outline has been staked out vegetation should be removed and any surface water courses should be diverted away from the site as topsoil is generally free digging scrapers bulldozers front end loaders and small hydraulic excavators are the most common equipment used in topsoil stripping bulldozers can be used for pushing material onto piles for further excavation by front end loaders or hydraulic excavators alternatively they can support scraper operation by ripping soil or by pushing scrapers along where they do not have enough traction graders are mostly used for precision applications such as haul road construction haulage distance is an important consideration in choice of equipment at short haul distances scrapers and bulldozers are more economic whereas a more conventional excavator truck haulage operation tends to be more economical at longer haul distances before the bedrock is reached the exposed soil may be a large potential source of dust and a water bowser or tank truck a mining truck that has been adapted for the distribution of water may be required for dust suppression in many operations topsoil storage is required for reclamation purposes at the end of mine life in some cases separate storage of different topsoil and subsoil layers may be necessary to ensure quality of the material depending on the duration of topsoil storage revegetation and erosion control may be required in some operations the excavation may never progress into consolidated material and the practices discussed here may also apply to the excavation techniques used for ore overburden removal removal of overburden is often required before extraction of ore can begin regarding materials handling there are three important differences between ore and overburden 1 overburden is not beneficiated and will generally not generate any revenue 2 overburden tonnages almost invariably exceed ore tonnages in an open pit mine 3 the rock mass characteristics are often different from that of the ore the first two points imply that handling of overburden and related costs should be kept to a minimum to minimize costs related to the handling of overburden it is often blasted to a coarser fragmentation than ore and in many cases excavated and hauled by larger capacity equipment as a result in many operations

the stripping of overburden is contracted out drilling blasting excavation and haulage practices for consolidated material will be discussed in more detail in the following sections drilling and blasting drilling and blasting comprise the first two of the four main stages in the production cycle of an open pit mine and the most common method of rock breaking other rock breaking methods such as mechanical breaking and surface miners can generally not compete in terms of either production rate or economy and will not be discussed in this chapter blast design blast design is the first and most crucial step in drilling and blasting first and foremost blast design is an iterative process where important factors such as the required fragmentation production and muck pile shape are used as a starting point for determining optimal drill hole diameter depth and inclination subdrilling explosives type and detonation timing hopler 1998 importantly operating costs of both the mine and the processing plant are directly related to the fragmentation achieved during blasting bhandari 1997 bench height and subdrilling requirements dictate drill hole depths subdrilling is the term used for the length a blasthole extends beyond the excavation level this is done to reduce the risk of equipment damage as a result of poor floor conditions which in turn is governed by geological features and the strength of the rock mass figure 10 1 4 shows a basic blast and blasthole geometry bench height is generally fixed by ore body characteristics and geometric and geotechnical considerations and is taken as the starting point for blast design selection of a suitable drill hole diameter is a complex process taking into account a host of factors related to production requirements rock mass characteristics environmental considerations and equipment selection hopler 1998 in general it can be said that larger drill hole diameters can be operated at larger burdens and spacings however this does result in larger fragments compared to smaller diameter holes at the same powder factor assuming a fixed bench height a good indication of hole diameter d is given by bhandari 1997 as d h 120 where h is the bench height in meters when determining the blasthole diameter it should be taken into account that there is an inverse relationship between hole diameter and operational costs bhandari 1997 typical values range from 83 to 350 mm depending on the scale of the operation drilling patterns e g burden spacing ratio vary substantially in size and patterns are tailored to specific operations there are many ways of calculating spacing s and burden b most of which are based on hole diameter the following rules are considered a good starting point for the estimation of the spacing and burden hustrulid 1999 b k d where k is a constant and d denotes hole diameter in meters and s 1 15 b where b denotes burden in meters the cons

tant k is dependent on the strength and density of the explosive as well as rock blastability it ranges from 20 in dense rock with light explosives to 40 in light rock with heavy explosives but typically it lies between 25 and 35 hustrulid 1999 in strong or blocky rock and to achieve optimal fragmentation conservative values should be used when calculating the burden typical values for the burden range from 3 m in smallscale operations to 10 m in very large scale operations the relationship between burden and spacing the burden spacing ratio can be varied according to the chosen blasting pattern square patterns s b are easy to lay out but result in poor charge distribution bhandari 1997 elongated patterns s b are preferred in hard breaking rock and when there are problems with back break hustrulid 1999 staggering a pattern further complicates layout but due to superior blasting energy distribution results in better fragmentation if there are problems with back break or when superior face angle control is necessary presplitting can be done with a smaller drill rig stemming is placed on top of the explosive column to ensure efficient use of the explosive energy and to reduce air overpressure drill cuttings are often used for stemming this is a cheap alternative to inserting specialized stemming material but it is less efficient at containing blast energy possibly resulting in unsatisfactory blasting results e g vertical flyrock and oversize blocks where possible angular material is preferred as by nature it tends to lock in place better during the detonation process further improving confinement of the explosive pressure appropriate stemming chip size lies in the range of 10 of the blasthole diameter a good approximation of stemming depth is 0 7 1 b and is commonly between 2 and 7 m after a drilling pattern is established a delay sequence should be fitted to this pattern the first consideration in determining delay intervals is the availability of free faces a blast should be initiated at the free face and aim at maximizing the use of the free face throughout the blast when there are no free faces available e g a box cut or sump blast a diamond cut is the best option displacing rock upward in the case of one free face a chevron pattern v pattern is recommended although a row by row pattern can also be used bhandari 1997 the angle of the v can be varied according to the local geological conditions and the desired blasting result when there are two free faces an echelon pattern usually produces the best results figures 10 1 5 through 10 1 8 show different standardized blast designs with relative detonation sequencing of the rows other cuts exist but are generally used in more specialized applications after a delay sequence has been established appropriate delay intervals can be assigned to rows or individual holes regarding delay intervals bhandari 1997 recommends 3 6 ms m o

f effective burden i e at the time it is blasted and not when it is drilled apart from the drilling pattern other important considerations during the selection of suitable delay timings are safety of the blast geology prevention of surface cutoffs vibration reduction and fragmentation requirements delay timings should be customized to prevailing geological conditions even within the same operation the shape of the muck pile required by the excavator is another consideration during blast design high compact muck piles are generally preferable for rope shovels and hydraulic excavators whereas a low flat muck pile is better for front end loaders hustrulid 1999 the delay pattern point of initiation and number of rows are the main influences on muck pile shape the higher the number of rows in a blast the larger the vertical component of rock movement and the higher the resulting muck pile bhandari 1997 the mining industry is becoming increasingly aware of the benefits of achieving a good fragmentation during blasting most importantly drilling and blasting is comparatively the cheapest method of comminution therefore achieving good fragmentation at this early stage can have a significant positive impact on the efficiency and costs of downstream comminution processes borquez 2006 furthermore better fragmentation allows for better use of the capacity of the excavation and haulage equipment in a mine on top of that optimization of blasting at a specific site may suggest that the same results can be obtained by using less explosives and it may reduce the amount of oversize boulders produced with these considerations in mind it becomes clear that determining the optimal fragmentation is a function of not only the effectiveness of the drilling and blasting process but also of excavation haulage and the downstream comminution processes the first step toward obtaining optimal fragmentation results is adopting a blast design aimed at producing the best fragmentation generally this means implementing a more closely spaced drilling pattern especially a lower burden with smaller diameter blastholes and more accurate timings but the exact blast design depends on a host of site specific parameters ongoing research is aimed at establishing the most influential factors in fragmentation and how blast design can be geared toward optimized fragmentation using these factors application of high precision gpss accurate drill guidance and drill monitoring have made it possible to drill blastholes with very little deviation together with the use of electronic detonators these two fairly recent advancements in drilling and blasting have made it possible to consistently produce optimal fragmentation during a blast these developments are further aided by the introduction of imaging software that can analyze the fragmentation of blasted material allowing for an iterative approach toward optimal fragmentation drilling prod

uction drill rigs are usually truck or crawler mounted and are powered either by a diesel engine or an electric drive pull down and hoist forces are applied by either hydraulic or chain hoist systems a range of systems is available for monitoring machine health and the drilling process production drill rigs are divided into rotary top hammer and down the hole dth hammer drill rigs rotary drill rigs rely on a pull down force transmitted through a rotating drill string usually with a tricone bit for the cutting action australian drilling industry training committee 1997 rotary drill rigs are generally most efficient in medium to hard rock and in holes with a diameter larger than approximately 170 mm hole depths can extend to more than 80 m in extreme cases top hammer drill rigs transmit the hammering force from the drill rig through the drill string down the hole they are preferred for hole diameters up to 140 mm depths down to 20 m and mostly used in small scale operations and precision applications such as secondary breaking hole straightness and energy loss at drill string joints are the main factors limiting the use of this type of drill rig for deeper and larger diameter holes dth hammer drill rigs rely on compressed air for operating a piston at the end of the drill string to provide the hammering action common applications include presplitting dewatering holes and other applications where high accuracy is required although they are also used for blasthole drilling dth hammer drill rigs are the most efficient drill rig type in hard to very hard rock drill hole diameters for dth hammer drill rigs commonly lie between 140 and 170 mm and depths of up to 40 m are feasible selection of the most suitable hole size and drill type for a particular mining operation is a function of balancing projected operating and capital costs with the required rock fragmentation wall stability grade control and production requirements generally drilling and blasting is the bottleneck in terms of time consumption in the drilling and blasting cycle it is absolutely essential for the overall productivity of a mine that muck pile volumes are sufficient to keep excavators and the haulage system used to the highest degree at all times hopler 1998 drilling productivity is dependent on rock hardness drill rig and bit selection bailing air volume and engine capacity rock hardness is the main determinant in the drillability of a material and the drill rig and bit should be selected for the prevailing conditions engine capacity is the most important factor in fitting a drill rig to the drillability of the material as it determines torque rotation speed and pull down force of the rig bailing air provided by an onboard compressor is used to clear broken rock from the bottom of the hole the airflow should be sufficient to clear rock chippings out of the hole but not so high as to cause excessive fugitive dust generation wear on th

e drill string and excessive fuel electricity consumption blasting ammonium nitrate fuel oil anfo is the most common and cheapest surface blasting agent followed by emulsions and slurries the ingredients making up the explosive substance are carried to the blasting location in separate compartments of a specialized truck for safety reasons the ingredients making up the explosive substance are generally not mixed together by the explosives truck until it is on site loading the blastholes optimal fragmentation is usually achieved when explosives are distributed so that the lower third of the hole depth contains half of the explosive charge hopler 1998 if high drilling costs or problems with fragmentation are experienced it can be advantageous to use stronger explosives or deck charges or add additives to increase explosive energy bhandari 1997 shock tube detonating cord and trunkline downhole combinations of these two systems are the most common surface detonation systems pyrotechnic millisecond connectors are the most common delay mechanisms although in recent years electronic detonators have rapidly been gaining ground because of unrivalled delay timing accuracy in most applications a detonator is used to set off a primer or booster that will in turn initiate the explosive charge before charging a blasthole it is good practice to check for water stagnant or influx and unexpected voids and to verify drilling was done to the planned pattern hole depth and inclination if water is found the hole should be dewatered a polyethylene liner can be inserted and or a water resistant explosive can be used secondary blasting may be required to break oversize boulders that are too large for the primary crusher mudcapping and blockholing are the two most common secondary blasting methods mudcapping involves molding an explosive to a rock surface and covering it with mud blockholing requires drilling a hole in the rock and charging it with explosive cartridges both processes are expensive and may well produce excessive air overpressure and flyrock it is essential to be able to see all sides of the boulder in the case of blockholing due to the possible presence of a misfire from the initial blast alternatively mechanical breakers can be used to break oversize boulders but this technique is often inefficient when dealing with competent rock types excavation excavation is the third main stage in the production cycle in a mine depending on the size of the operation and the type of haulage system electric rope shovels hydraulic excavators or in some cases large front end loaders are used in open pit mining operations equipment rope shovel bucket capacities have risen to just over 100 t the largest bucket capacities for hydraulic excavators currently available are slightly lower than that of rope shovels topping at 90 t front end loaders normally have capacities of around 36 t although there are larger models with cap

acities of up to about 90 t until recently rope shovels were the sole players in the 60 to 100 t range however there are now several hydraulic excavators competing directly with rope shovels in this size range rope shovels are still the standard in high production low cost mines because of their reliability and long life in the intermediate size range 30 to 60 t the choice of equipment is to a large degree site dependent opting either for the flexibility of a hydraulic excavator or the reliability of a rope shovel in the smaller size range 30 t bucket capacity hydraulic excavators account for almost all orders and are slowly replacing rope shovels the net digging force in hydraulic excavators is a combination of break out or curling force bucket tilt cylinders boom force boom cylinders and the crowd force stick cylinders in rope shovels the net digging force consists of the crowd force crowd machinery and rope pull hoisting machinery for hydraulic excavators face shovel and backhoe configurations are available face shovel configurations are preferred in harder rock and with higher rock faces backhoe configurations allow for more selective digging and faster cycle times as swing angles can be reduced when loading a truck on a lower level front end loaders are the preferred choice for specialist jobs where their mobility and flexibility can be used to a maximum extent examples include blending operations road and infrastructure construction working in the confined space of a drop cut and as support or backup for larger excavators excavation equipment can be evaluated in terms of productivity metric tons per hour and efficiency cost per metric ton the bucket fill factor is an important consideration in the overall productivity of an excavator and is dependent on the truck coverage diggability of the material operator skills and net digging forces from the excavator other important factors in achieving acceptable productivity and efficiencies from excavators are matching the trucks to excavator sizes ideally three or four loading passes selecting the right excavator for the bench height and providing enough working space for the excavator and trucks to operate hustrulid and kuchta 2006 excavation practices excavation of a new level often begins with a drop cut alternatively when excavations are still above topography i e on a hillside a new excavation is begun from an access road without the need for a drop cut the confined working space in a drop cut often requires the use of a backhoe excavator from the top level or a front end loader driving in and out of the drop cut alternatively a truck can turn and reverse into position next to a small excavator in the drop cut lateral extension of the bench is done through frontal or parallel cuts frontal cuts involve cutting adjacent niches into the muck pile rather than having an excavator moving with the muck pile parallel to the bench

wall as done in parallel cuts hustrulid and kuchta 2006 as shown in figures 10 1 9 through 10 1 11 trucks can drive by or stop and reverse into a position next to the excavator hustrulid and kuchta 2006 have written a comprehensive description of different possible modes of truck excavator operation according to them available working space the necessary swing angle of the excavator and truck positioning time are the major considerations in the selection of the type of operation drive by operations are most suitable for parallel cuts optimizing efficiency by reducing positioning time of the truck frontal cuts can require excessive swing angles by the loader making it inefficient the disadvantage of drive by operations is that they require larger working areas and ideally a separate ingress and egress route from the loading area stop and reverse operations can be employed in combination with both parallel and frontal cuts they require less operating space and are more efficient from the excavator point of view when there is sufficient space on the bench a truck can turn without the need for reversing with regard to operating techniques it is generally considered good practice to excavate the farthest or hardest to dig material in the first pass while waiting for the truck to position the intermediate passes can be positioned where the operator deems fit and the last pass can be used for floor cleanup this is only necessary when there is no dedicated support equipment for floor cleanup correct load placement is crucial in avoiding spillages and excessive truck wear ideally loads are centered on the center line of the body longitudinally above the hoist cylinders of the truck laterally with no material on the headboard and enough freeboard on the sides and rear caterpillar 2006 considering optimal loading of dump trucks an original equipment manufacturer oem recommends what they call the 10 10 20 payload policy this policy states that no more than 10 of loads may exceed 10 over the target payload and no loads may exceed 20 of the target payload caterpillar 2006 average cycle times range from 25 to 27 seconds for hydraulic shovels in backhoe and face shovel configuration respectively to an average of 35 seconds for rope shovels and 38 seconds for large front end loaders caterpillar 2006 in well fragmented rock rope shovels commonly have bucket fill factors around 100 to 105 for backhoe excavators this lies between 80 and 110 and large front end loaders generally can attain bucket fill factors between 90 and 110 bucket fill factors of more than 100 are achieved by heaping material in the bucket backhoe excavators are most efficient on benches no higher than the length of the stick with short swing angles loading a truck on a lower level some of the main productivity losses for excavators are idle time while waiting for trucks excavator relocation especially with rope shovels poor op

erator skills bad digging conditions i e poorly fragmented rock wet material poor underfoot conditions incorrect muck pile shape and dimensions and unplanned downtime for front end loaders there are the additional requirements of good floor condition maintenance and good drainage to prevent excessive tire damage careful scheduling can increase productivity by reducing idle time and excavator relocation time reduction of excavator cycle times can also improve the productivity of a mining operation markedly to illustrate this point in a typical operation with all other factors unchanged a reduction of 5 in the excavator cycle time can equate to up to 40 extra truckloads per day implementing cycle time improvements suggested by personnel oems or consultants is crucial in capitalizing on possible cycle time reductions among the possible improvements are better floor condition maintenance adequate operator training and excavator optimized blast design to ensure the correct fragmentation and muck pile shape furthermore excavator manufacturers play a pivotal role in providing technological advances such as increased engine performance monitoring and automation to reduce possible cycle time grade control reconciliation and selective mining open pit mining has historically been considered a bulk mining method with low selectivity however a global trend toward increasingly challenging open pit mining conditions combined with the need to control costs and optimize mill performance have accentuated the need for optimum fragmentation selective mining and improvement in grade control in line with this need technological advances make selective mining increasingly feasible by decreasing the selective mining units the minimum volume of material that can be extracted by an excavator without significant dilution the ultimate goal of grade control and selective mining is to ensure a constant mill feed as well as minimizing ore loss and dilution depending on the operation profits from improved grade control grade reconciliation and selective mining can be larger than from any other operational improvement and as such they deserve thorough attention sinclair and blackwell 2002 grade control requirements and practices are largely dependent on the commodity first the commodity price controls the implications of ore loss and management has to justify the extra expenditures relating to selective extraction second the increased mill performance due to lower dilution must justify any additional actions required during the mining processes last the style of mineralization often commodityspecific dictates whether grade control is geared more toward ore barren rock discrimination or whether it is focused on grade and stockpile control davis 1992 unbiased sample acquisition meticulous sample processing and accurate sample analysis on a short time scale are keys to effective grade control in hard rock operations sam

pling blasthole cuttings is the most effective option for grade control although sometimes a drill rig is dedicated solely to grade control drilling annels 1991 in this case timing of sample acquisition is crucial because of the risk of contamination during drilling operations mining unconsolidated material often employ a continuous trencher commonly referred to as a ditch witch to produce samples best results are obtained by trenching at right angles to the predicted ore body orientation sample results should be used to model grade distributions in planning or geostatistical software while taking into account the minimum selective mining unit of an excavator on the basis of the produced models a clear demarcation of ore and barren rock in active operating areas can be provided often done using colored flags or pegs hanging colored ribbons down the face can further aid excavator operators in discerning ore and barren rock the next step in grade control is the selective mining of material a distinction should be made between free digging material e g laterites and consolidated material because drilling and blasting aggravates potential ore losses and dilution davis 1992 in free digging material excavators often work across the strike of the ore body flitches refer to the steps or thin lifts in which a bench is mined depending on ore body geometry and the minimum selective mining unit of an excavator they can be as small as 1 m although 2 5 m is a more common size ideally mineralized portions of the flitch are removed prior to the barren rock to minimize risk of dilution and ore loss in a drilling and blasting operation it is important that excessive intermixing and movement of blasted material is inhibited when a whole blast is located in ore spacing and burden can be reduced to increase fragmentation and subsequently reduce comminution costs alternatively when a blast only breaks up barren rock increased spacings and larger burdens reduce fragmentation and decrease production costs if ore and barren rock are intermixed on a subblast level they are blasted together before demarcation of both zones bulldozers can be used to separate ore and barren rock before excavating although this can result in smearing of the ore or barren rock margin in any case supervising excavations closely is important to ensure correct dispatching of trucks and possibly to visually discern ore barren rock contacts during excavation after the ore is loaded into a truck it should be dispatched to the dump or the correct stockpile the use of modern equipment dispatching systems greatly aids in dispatching trucks to the correct destination apart from ore barren rock discrimination and assigning metallurgical grades to material grade control also provides a basis for reconciliation of mill production figures geostatistical models and pit production tonnages and grades davis 1992 discrepancies between the mine product

ion and mill production can serve as an indication of poor mine or mill performance a lack of communication between different departments in a mine sampling error lab error or errors in the geostatistical model haulage systems the fourth and last main stage of the production cycle in a mine is haulage rigid frame haul trucks have dominated haulage in open pit mining operations for decades although in some cases articulated dump trucks adts have proven a viable alternative and sometimes rail haulage is still being used furthermore longer haulage distances in many large pits availability problems with haul trucks and improvements in technology have revived interest in in pit crushing and conveying ipcc rigid frame trucks possibly in combination with trolleyassist hauling are the preferred choice for haulage in most open pit mines compared to adts they are far superior in payload capacity achieve better speeds in most road conditions and have lower maintenance requirements however in certain cases such as small scale operations and operations that struggle to maintain adequate surface conditions the flexibility and versatility of adts can pay dividends ipcc systems are another alternative to conventional truck haulage whether ipcc is economically viable is a function of production duration of the operation and the distance and vertical lift of the haulage route trucks payload capacities for rigid frame haul trucks currently range from around 25 t to just over 360 t depending on the truck size and manufacturer there is a choice between mechanical drive and electrical drive systems mechanical drive systems use a diesel engine in combination with a mechanical power train whereas diesel electric systems rely on a diesel powered alternator to generate electricity for electric motors mostly ac diesel electric ac systems dominate the larger truck sizes 150 t payload while payload capacities for adts generally do not exceed 50 t truck cycle times depend on the type of excavator capacity of the truck and haulage distance assuming good truck excavator capacity matching and good digging conditions trucks can be loaded in approximately 100 to 180 seconds although this can be longer for front end loaders spotting at the excavator typically takes between 40 and 60 seconds in the highly interactive system of today s open pit mine productivity of the haulage system is largely dependent on the performance of other activities in the mine notably the haul road and dump maintenance and the excavator efficiency for that reason problems with haul truck productivity and reliability can often be traced back to poor performance of other parts of the operation the operational interdependence of haul trucks and excavators comes to light during synchronization of their use and during loading production scheduling can reduce idle times for trucks and excavators payload monitoring and good communication between truck and

excavator operators is important when trying to achieve optimal loading similarly good operator training as well as a high degree of coordination communication and visual confirmation on the part of both the excavator and the truck operator is required for adequate truck spotting ideally excavator operators should communicate the correct position for a truck to the truck operator rather than relying on the judgment of the latter to get the truck in the right place good communication is especially crucial when double spotting trucks this method has the potential to reduce excavator and truck idle time but it is more complex than single spotting or drive by operations lastly effective dispatching can maximize the use of trucks and excavators by providing a better synchronization between the two other considerations in dump truck productivity are haul road performance floor conditions in active loading and dumping areas and retention of material in the truck s bed poor haul road performance e g haul road defects and high rolling resistance can reduce productivity and reliability of dump trucks likewise poor floor conditions in active loading and dumping areas e g benches and dumps can also affect productivity and reliability of dump trucks and especially their tires in both cases management of the floor conditions in a manner similar to that of haul roads can have a positive impact on haul truck performance additionally retention of material in both the excavator bucket and the truck bed can pose a challenge to operations especially in arctic conditions or where material has a high clay or moisture content adaptation of the truck bed design e g rubber floor mats or circulation of exhaust fumes through the bed to prevent freezing can alleviate this problem tire management tires are a basic constituent of a dump truck and in recent years tire shortage has been a major challenge for the mining industry prolonging tire life can result in big savings considering that off the road tires for large dump trucks can cost more than 50 000 2009 estimate while excessive downtime of trucks can result in even higher costs more than 80 of tires fail before they wear out of all failures approximately 45 are caused by cuts from spilled material and 30 by impacts with large rock fragments caterpillar 2007 maintaining the correct inflation pressure maintaining good floor conditions and ensuring good truck handling and tire awareness by operators throughout the mine are some of the main aspects that can increase tire life for truck operators especially when it comes to removing spillages good communication between truck operators and the road maintenance department is crucial analysis of scrap tires and monitoring of tire performance can provide valuable insight into causes of tire failure and possible prevention of premature tire failure furthermore as a response to tire shortages several major tire manufactur

ers now offer tire management systems these systems use software sensors integrated into tires and dedicated handheld tire monitoring devices to measure and benchmark tire performance trolley assist haulage trolley assist haul trucks are haul trucks that have been adapted from the standard diesel electric system to a system that relies on pantographs to connect to an electrified overhead line for power supply historically use of this system has been concentrated in southern africa but with rising diesel prices interest in trolley assist hauling from other parts of the world is increasing major infrastructures that need to be installed for the use of trolley assist haulage include the overhead lines truck conversion packages and trolley substations these conversion packages can be fitted on the majority of diesel electric trucks increased power supply from the overhead line compared to a truck based diesel generator allows maximum use of the capacity of the electric motor in a truck as a result reduced cycle times are possible and consequently truck fleets can be reduced this allows for productivity increases and possibly reduced capital investment costs related to purchasing fewer trucks furthermore as the diesel engine is idling while on trolley assist fuel consumption and ultimately time between engine overhauls can be reduced significantly lastly energy can be recovered into the trolley supply grid when trucks are moving downgrade there is no generic way to determine whether an operation would benefit economically from a trolley assist system savings related to trolley assist usage are directly proportional to the number of kilometers traveled on the trolleyassist line by the entire truck fleet hutnyak consulting personal communication other important factors to consider in determining the possible savings related to trolley assist haulage are the truck fleet size designed life of a ramp vertical lift of the haulage route and traffic densities as such trolley systems are not suitable for every operation first the number of trolley assist kilometers must be large enough to offset additional investments required for the trolley assist infrastructure this is most likely in large mines with a long life and an extensive diesel electric haul truck fleet second the difference between fuel costs and electricity costs must justify the transition to trolley assist haulage lastly trolleyassist haulage inherently reduces the flexibility of a haul road system by fixing haul routes therefore trolley assist hauling is economically most attractive to extensive mines with long permanent uphill haul roads and a large truck fleet in regions with high diesel costs relative to electricity costs higher haul truck speeds more traction and highly fixed routes increase the chance of rutting and other haul road defects the main adverse effects of this are reduced productivity and possibly pantograph damage when trucks

are rejected from the trolley line therefore haul road maintenance is even more important on trolley assisted haul roads the recent adoption of ac drives now allows trucks to connect to and run on trolley assist at variable speeds negating one of the main disadvantages in the past when they relied on dc drives furthermore sensors can now aid operators in staying underneath the overhead line in conclusion it can be said that trolley assist hauling can be economically viable especially now that technological advances have solved some former dc related disadvantages of trolley systems however because of mine specific circumstances economic viability of trolley systems should be evaluated on a mine by mine basis in pit crushing and conveying systems ipcc systems typically rely on gyratory impact cone or jaw crushers to feed an overland conveyor belt that transports material to the mill or overburden embankment they can be classified into mobile and semimobile systems mobile systems are crawler mounted and are often fed directly by an excavator having capacities of less than 1 500 t h these systems are usually found in small open pit mines or quarries semimobile systems are mostly based on gyratory crushers fed either directly from trucks or from truck fed apron feeders they can only be moved with specialized equipment hence the name semimobile having far higher capacities up to 14 000 t h than fully mobile systems these systems are suitable for mines with very large production tonnages the most common conveyor belt configuration is a standard trough type conveyor however this type of conveyor belt suffers from limited curve radii minimum of 400 m for large overland conveyor systems and slope angles maximum of 16 18 it can scale pipe conveyors are a relatively recent development used to negotiate tighter curves they are essentially rubber conveyor belts folded into a pipe shape with idler rollers as idlers constrain the belt from all sides far tighter curves can be negotiated a further advantage is the reduction of spillages and fugitive dust generation the disadvantage of a pipe conveyor is its limited capacity to overcome the slope angle limitation conveyors can be led up switchbacks or a dedicated trench can be excavated for the conveyor belt at the desired angle alternatively one of several high angle conveyor systems can be used such as the sandwich design or the pocket lift design the sandwich design as the name suggests sandwiches materials between two conveyor belts kept in place by idlers the pocket lift design relies on material being carried in pockets created by wrinkling the belt a system similar to the pipe conveyor can also be used for high angle conveying provided that material is sufficiently confined as mentioned earlier the economic viability of ipcc depends on production tonnages duration of the operation haulage distance and vertical lift as a general rule it can be said

that if production exceeds approximately 100 000 t d when haulage distances surpass 5 km or when the vertical lift exceeds 250 m and if the installation can be in operation for at least 7 8 years the benefits of ipcc can offset the higher capital costs of this installation the economic benefits of ipcc rely on the potential to significantly reduce truck haulage distances and consequently fuel consumption haul road and truck maintenance costs and labor requirements furthermore operations using ipcc are less prone to tire equipment or labor shortages other advantages over conventional truck haulage systems include lower carbon emissions and improved safety the resulting reduction in overall mining costs has led to a revived interest in ipcc ipcc especially semimobile systems reduces the flexibility of a mining operation with respect to pit expansion and pushbacks additionally crusher moves and unplanned downtime of the conveyor belt can have serious impacts on the overall productivity of the system careful selection of crusher locations should minimize downtime due to crusher relocation advantages of ipcc systems are best realized in large high volume open pits with a long mine life however regardless of mine life and size materializing the potential cost savings still requires a detailed economic feasibility study incorporating site specific operational geological and economical aspects ancillary equipment and mine services ancillary equipment and mine services also referred to as auxiliary operations are all activities supporting but not directly contributing to the production of ore hartman and mutmansky 2002 among the more prominent and important auxiliary operations in an open pit mine are power fuel supply and distribution haul road construction and maintenance inpit water management and the communications infrastructure these activities do not generate revenue directly nonetheless it is critical for the overall efficiency of a mining operation that these activities are given adequate attention bulldozers front end loaders graders water bowsers and fuel lube trucks are some of the most important pieces of ancillary equipment graders and water trucks are absolutely essential to haul road maintenance which in turn is one of the most important elements of an efficiently operating surface mine the main role of bulldozers and front end loaders is maintaining active loading and dumping areas preventing tire damage and ensuring effective loading and dumping the increasing awareness of health and safety within the mining industry has raised attention for mine rescue service many large open pit mines have one or more ambulances a fire truck or firefighting equipment and some have advanced rescue trucks with highly trained crews available 24 hours per day to respond to emergencies many operations also have an airstrip or heliport locations for emergency life flight services if needed with many lar

ge excavators running on electricity the power system is undoubtedly the most important mine service electricity can be supplied either by a utility company often more economical or by an on site generator in remote areas typically an open pit primary distribution system consists of a ring bus or main that partially or completely encloses the pit the distribution voltage is normally 4 16 kv but 7 2 6 9 or 13 8 kv are sometimes used morley 1990 radial ties complete the circuit from the bus to the switchhouses located in the pit where necessary substations are employed where equipment voltages are lower than the main power loop the power distribution evolves throughout a mine life substations and other components of the power distribution system are mobile so they can follow mining equipment into a new working area more details on mine power supplies are found elsewhere in this handbook in pit water management lighting and communication infrastructure are three other important mine services the benefits of efficient in pit water management are discussed in the in pit water management section in this chapter flood lights are important as they enable around the clock production which markedly increases productivity at a modern open pit mine especially at high latitudes the communication infrastructure in mining operations is rapidly evolving into an essential part of the operation as a response to the ongoing increase in complexity of openpit mining operations while initially used mainly for radio communications the communication infrastructure now also carries information essential for equipment dispatching and monitoring discussed in more detail in the next section a well implemented communications structure in a surface excavation can improve safety efficiency and productivity by enabling real time dispatching and monitoring of mining equipment as well as voice and video communications additionally mine services such as the pumping system can now be monitored and controlled remotely slope stability monitoring can be centralized to a large degree and cameras can be located in critical areas such as the digging face primary crusher and other key areas several different types of networks are available for surface excavations and the choice of system is site specific open standard wireless local area networks such as ieee 802 11b g n are becoming commonplace as they are cheaper and more versatile than proprietary radio systems satellite phones or terrestrial phones depending on the application wireless networks can comprise two or more discrete points i e point to multipoint networks or as a more flexible all encompassing mesh network e g bluetooth zigbee ieee 802 15 4 or similar standards equipment dispatching and monitoring advances in gps positioning mechanical health monitoring and production monitoring are contributing to an everincreasing trend toward automation of open pit mines t

ruck dispatching is now commonplace in most operations and the benefits and potentials of various other monitoring systems are increasingly being recognized all major oems include a basic machine management package with their equipment their most important function is to monitor the health of vital machine functions such as the power train suspension and brakes to detect abnormal conditions or impending failure by enabling proactive rather than responsive maintenance operator safety can be improved while significantly reducing downtime and maintenance costs the option exists to have oem engineers analyze the data and make maintenance recommendations remotely these packages can be expanded with additional features to increase productivity such as payload monitoring and road analysis in trucks bucket load monitoring and motion tracking for excavators and vibration reduction feedback systems gps based drill positioning systems and drill progress monitoring for drill rigs equipment dispatching systems are offered by most oems and several third parties originally these gps based systems were geared toward dispatching of dump trucks to the correct areas however by applying the same principles to drill rigs and to ore blending auxiliary and other mobile support equipment modern systems are better described as equipment management systems integration of payload monitoring cycle times and other production related variables have further revolutionized equipment management in mines tracking these parameters over time allows benchmarking and bottleneck identification in the production cycle by providing benchmarks and highlighting previously unnoticed bottlenecks in the production cycle modern equipment management systems can prove a valuable tool in the optimization of an open pit operation extensive research is being done into the use of autonomous surface mining systems and the first pilot scale tests on the use of haul trucks and drill rigs are now under way however the use of autonomous surface mining systems is still in its infancy and the realization of the huge potential of these systems will be an ongoing process in the next few decades an in depth discussion of current developments in autonomous mining systems is found in chapter 9 8 of this handbook production planning adequate production planning is absolutely essential in achieving the highest possible return from a mining operation caccetta and hill 1999 it is a complex process for evaluating a host of variables including ore body geometry mill feed requirements and equipment fleet related factors to achieve the required production accordingly in recent years a large amount of research has been dedicated to improving mathematical and financial principles behind production planning on the basis of these principles pit optimization and planning software have been developed and included in major mining software packages to aid in production planning in

many cases production planning is not simply a case of planning the mining sequence for an ore body rather it should be a cost benefit analysis not only on the extraction of ore but also on the required development and installation of infrastructure required for ore extraction and the interaction between the two in terms of economic performance safety availability of labor and availability of equipment hall 2009 depending on the type of production planning a host of factors such as staff and equipment fleet dispatching and availability pit expansion processing alternatives and commodity prices come together in production planning to meet targets set by the management of a mining corporation it may be contracted out to a consultancy or it can be done in house by engineers at the operation or sometimes at a dedicated office production planning can be divided into long term and short term planning long term or strategic planning concentrates on defining a goal and as such is undertaken on a multiple years to life of mine time scale kear 2006 shortterm or tactical planning on the other hand is more geared toward achieving a goal and is done on a time scale ranging from day to day planning to multiple year production plans inherently long term planning is more concerned with providing frameworks for pit design and expansions e g pushbacks production schedules rehabilitation plans and equipment selection whereas short term planning focuses on equipment use maximization of productivity and ultimately meeting productions targets in modern operations equipment dispatching systems play an important role in short term production planning short term production schedules should have a degree of flexibility in them to respond to unanticipated changes in the production environment these changes range from simple matters such as a haul road defect to complicated issues such as a slope failure assessment and where necessary adjustment of short term production schedules as a result of these changes should be implemented in a timely fashion open pit mining and the environment as mentioned in the introduction of this chapter the influence of mining on the environment is becoming an increasingly important consideration before during and after the mining process as such discussions of the environmental impacts as well as mine closure and rehabilitation of open pit mines are warranted furthermore to connect several other deliberations within this chapter a discussion of geotechnical considerations and slope monitoring is included together with a section on in pit water management geotechnical considerations and slope monitoring throughout this chapter there have been several references to the importance of adequate geotechnical design and slopestability monitoring of an open pit mine subsequently a generic discussion of these topics is appropriate readers are referred to chapters 8 3 and 8 5 of this handbook

for a thorough discussion of the subjects of geotechnical instrumentation and slope stability rock mass parameters are an important consideration from the feasibility study onward they not only affect pit layout and geometry but also blasting practices and to a lesser extent mining equipment selection and the layout of the comminution circuit wyllie and mah 2004 most importantly rock mass parameters directly determine the steepest possible slope and face angle while maintaining an acceptable factor of safety thereby having a major influence on the profitability of an operation furthermore they can rule out the use of certain areas of an excavation for important infrastructure such as the main haul road in an active excavation continual slope monitoring is crucial in predicting and preventing slope failures and when failure is imminent mitigating the effects of a slope failure a comprehensive slope stability monitoring program reduces the risk of major production delays or even sterilization of part of a reserve permanently as a consequence of a slope failure moreover it ensures overall safety of personnel and equipment in an operation a survey showed oversteepened slopes failure to appreciate the effects of water and rockfalls to be the main causes of injuries fatalities and damage to equipment sullivan 2006 adequate design and monitoring can largely prevent these situations from occurring another situation where pit slope monitoring is important is when there are active underground workings in close proximity to an open pit mine crown pillar failure or caving related subsidence can permanently cease surface excavation activities slope stability monitoring techniques can be divided into surface and subsurface monitoring techniques wyllie and mah 2004 surface monitoring techniques include visual survey direct measurement techniques prism monitoring laser systems and radar systems visual survey includes visual inspection of slopes as well as mapping of structural discontinuities and more recently photogrammetry although the discontinuity mapping and photogrammetry can provide valuable insights into failure mechanisms that cannot be gained using other techniques they do not provide quantitative data on slope stability and therefore should be supplemented by at least one of the methods discussed in the following paragraphs direct measurement techniques include crack width meters tilt meters and other similar devices these are low tech methods to provide accurate indications of minor displacements in a possible failure zone prism monitoring relies on the use of total stations at permanent stable reference positions to determine the distance to prisms mounted in areas of instability from the change in spatial coordinates of targets over time the displacement velocity and direction can be calculated it is a very cost effective method but it is vulnerable to atmospheric conditions such as excessive dust

or mist laser systems rely on a laser scanner to produce a threedimensional point cloud model of a slope the higher density of points compared to prism monitoring makes laser scanning more comprehensive than conventional surveying techniques a further advantage of laser scanning is that it can aid in photogrammetry and the mapping of discontinuities radar systems are similar to laser systems but provide higher accuracy the drawbacks of radar systems are that they can only monitor one single area at a time compared to a broader picture as gained through laser scanning and they are generally more costly however because of the unrivaled accuracy submillimeter they are often used to monitor the highest risk areas such as working faces or areas of known instability subsurface monitoring techniques include time domain reflectometry borehole probes extensometers and inclinometers these techniques rely on measurement of changes of the inclination or other characteristics of a borehole that could indicate deterioration of stability additionally seismic monitoring techniques are used these rely on geophones registering acoustic emissions associated with failure events the most cost effective approach to slope stability monitoring is generally a combination of several of these techniques where they are used to complement one another for instance laser systems or prism monitoring can be used to determine overall stability of pit slopes and identify possible failure zones if instability of a slope is detected extensometers or radar systems can be used for more precise determination of movements in this area a last important consideration in slope stability is the presence of groundwater phreatic levels in and around a mine are crucial for maintaining pit wall stability especially in areas with clayey material or where the rock is heavily affected by structural discontinuities wyllie and mah 2004 if the climate has periods of prolonged frost the freezing thawing cycles can further aggravate the negative effects of groundwater on slope stability piezometers are the main tool for determining groundwater levels these together with rain gauges can act as an early warning system and serve as a basis for adjustment of the rate of water extraction from dewatering wells to prevent groundwater induced failures apart from the geotechnical implications of groundwater in and around a pit there are also major production related considerations associated with in pit water these are discussed in the following section with mining being a business enterprise geotechnical design monitoring and stabilization of an open pit mine is ultimately a matter of economics balancing the benefits and costs of stabilization against the costs and implications of a slope failure pine 1992 wyllie and mah 2004 this is in sharp contrast to civil engineering where the social and financial consequences of failure can be far more extensive pine 1992

a combination of this different approach to risk management together with the bigger scale of potential slope failures means that civil engineering solutions to slope stabilization are generally not feasible in surface excavations furthermore surface excavations can possibly tolerate a degree of slope failure that would be unacceptable in civil engineering applications wyllie and mah 2004 as a result of this lowering of the water table and decreasing the slope angle are often the only practical options in surface mining although in some cases applying civil engineering solutions has been economically viable wyllie and mah 2004 in pit water management responsible water management is essential in minimizing the environmental impact of most mining operations furthermore there are considerable geotechnical operational and economical advantages to in pit water management i e more stable pit walls and a lower stripping ratio a sound approach to in pit water management requires the development of drainage strategies for both surface and groundwater and continuous monitoring of the performance of the water management plan department of resources energy and tourism australia 2008 for this a thorough assessment of local geology rock mass characteristics hydrogeology surface hydrology and local climate are required when deciding on dewatering methods it is important to consider not only the above mentioned factors but also the logistics related to openpit mine dewatering this includes the interaction between the chosen dewatering method dewatering related infrastructure i e power supply and water transport from the well and unit operations in a mine atkinson 2000 to maximize the advantages of dewatering sections of an open pit mine must be dewatered before mining begins ideally wells drain holes pump lines and other dewatering infrastructure are situated such that they do not require rerouting as mining progresses additionally the destination of water removed from the pit is an important consideration it can be reinjected elsewhere used in mineral processing operations or it can be treated and discharged into surface water courses there are several advantages to a correctly implemented dewatering program first and foremost dewatering pit slopes improves and maintains slope stability this results in safer working conditions and allows for steeper slopes lowering the stripping ratio second a lower moisture content of blasted material increases diggability and reduces haulage costs as dry material has a lower mass than wet material and there is less retention of material in the excavator bucket and the truck bed detrimental effects of wet haul roads include unsafe traffic conditions more tire cuts and increased rolling resistance lastly water influx into blastholes is decreased reducing the need for blasthole dewatering or the use of more expensive water resistant explosives rain can constitu

te one of the main influxes of water into an open pit as such a thorough understanding of the typical local climate and its extremities e g monsoons is invaluable when formulating the water management plan for an operation rain gauges can be a further aid monitoring rainfall and providing an indication of increased influx and possibly the demand to adjust the pump rate stream diversion and dewatering wells are the main water management activities outside a pit perimeter inside the pit perimeter dewatering wells sumps horizontal drain holes and in some cases drainage adits or grouting are used for water management stream diversion both of permanent and ephemeral streams is done during the development stage of a mine before or concurrent with topsoil removal depending on the hydrogeology dewatering wells can be situated within pit boundaries or outside of them atkinson 2000 where the direction of flow is mainly lateral dewatering wells outside the pit perimeter are generally more effective a further advantage of dewatering wells outside the pit perimeter is that they can be installed before mining commences however they are less effective at preventing vertical inflow through the pit floor to mitigate this in pit vertical dewatering wells are more effective atkinson 2000 this type of well creates more drawdown in the pit than dewatering wells outside the pit perimeter but they cannot be installed prior to mining and it generally also requires more complicated logistics in pit horizontal drain holes are used for locally depressurizing targeted areas atkinson 2000 they are an inexpensive method that can significantly increase slope stability because the small scale of these holes allows them to be installed quickly targeting specific problem areas however they can only be installed after mining begins they suffer from freezing effects in arctic areas and water removal usually requires a sump downstream of the drain holes sumps are catchment basins at the base of a pit that serve the purpose of collecting in pit water so it can be pumped back out grouting refers to the injection of chemicals that block pores in the rock to provide a barrier that prevents groundwater influx this is a costly option that is only effective if there is a very well defined geological feature producing the majority of water influx in a pit drainage adits around a pit shell serve the same purpose as drain holes because of the labor involved it is a very costly and inflexible option that is becoming increasingly scarce environmental issues in recent years the pressure on mining companies to minimize the environmental impact of their operations has increased considerably as a result prevention and mitigation of detrimental effects to the environment are now high on the agenda of modern operations some discussion of environmental considerations related to mining in general is available elsewhere in this handbook so this cha