text
stringlengths 1.99k
3k
|
|---|
in engineering geology abrasion is significant in three main ways erosion of the earth s surface damage caused by abrasive minerals and rocks to machinery selection of minerals that are suitable for use as industrial and domestic abrasives this is a complicated topic that is not yet fully resolved matters of specific interest include the relative ease or difficulty of resistance to excavation drilling or cutting of rocks and soils susceptibility to abrasion of surfaces including aggregates in highway pavements machinery and natural stone used in buildings to abrasion abrasion is often a two way process with the harder material affected less by wear than the softer material in general abrasion increases with hardness grain size and angularity of mineral content type of cementation degree of alteration and discontinuities in the rock forces of impacts and the overall mechanical properties of the soil or rock mass mineral particles carried by dynamic media cause abrasion of natural landforms and buildings and constructions the media are wind sediment carried by the wind sculpts distinctive landforms especially in arid areas but also during dry periods in less arid areas particularly where vegetation cover is absent sea water and lakes breaking waves carry sand and coarser particles against coastlines causing undercutting of slopes and cliffs and consequent landslides the resulting cliff retreat forms abrasion platforms adjacent to the shoreline and wave cut notches fig 1 similar processes occur in large lakes rivers rivers carry sand and coarser particles depending on the strength of the current that cause channel scour and erosion of river banks with consequent changes in geomorphology and bank and slope stability ice debris frozen into the beds and lateral margins of glaciers and ice sheets erode and smooth adjacent rock surfaces these processes erode smooth and polish rock surfaces but also round and polish the debris that impact on those rocks plant machinery and other equipment are abraded during use causing wear and blunting and therefore contribute to significant costs of repair replacement and delays it is important to understand the potential for abrasion when costing engineering projects that involve drilling tunneling and mechanized excavation as well as grading cutting and shaping of mineral products such as aggregates and dimension stones majeed and abu bakar 2016 conversely abrasion is used in extraction of building stone by wire cutting techniques in which an armored wire and abrasives are used to cut and shape blocks a variety of minerals are used as abrasives selection of suitable pure or refinable materials depends on the minimum effective hardness these range from less demanding uses e g toothpastes and some domestic cleansers using calcite or feldspars to demanding industrial uses e g cutter heads or wires of strengthened metal and armored with ve |
ry hard minerals a variety of abrasiveness tests have been developed for different purposes currently there is no universally accepted test for soil abrasiveness but much research is in progress mirmehrabi et al 2016 there is also an issue of the scale of tests these can be at a real scale in the tunnel excavation and borehole by examining resistance but this procedure is expensive and too late to do more than adjust the pattern of works it is more usual to undertake laboratory tests using scaled down equipment on samples which is more practical but less representative of the natural situation an alternative option is provided by geotechnical tests there have been two main approaches to testing abrasion abrasiveness the earliest focused on relative hardness of constituent minerals friedrich mohs defined a 10 stage hierarchy on the basis of which a mineral was strong enough to scratch another in that sequence talc softest gypsum calcite fluorite apatite orthoclase quartz topaz corundum and diamond hardest other minerals are then placed in this sequence between pairs of the listed minerals based on their ability to scratch or be scratched mohs scale is a relative scale it was later developed by rosiwal into absolute values measured in the laboratory taking corundum as having a value of 1000 an approach for use in the field is given in mol 2014 hardness may be determined in the field or laboratory by rebound devices such as the schmidt hammer most rocks and soils contain a variety of minerals which are variably affected by diagenetic and weathering processes that affect hardness therefore tests on individual minerals while useful are not wholly adequate for engineering geology purposes which requires examination of mechanical properties of rock and soil masses mineral based texts also neglect the sizes and shapes of grains the cerchar abrasive test was developed to assess the potential abrasion damage to plant and equipment for instance cutter life in the field and is also significant for building and construction materials including dimension stone deliormanli 2011 it involves the use of an abrasive stylus to scratch a broken or cut surface of a sample strong correlation exists between the cerchar abrasivity index cai and rock strength and abrasion the rock abrasivity index was developed to take account of the content of abrasive minerals and the strength of the rock and is based on multiplying the unconfined compressive strength ucs and equivalent quartz content eqc of the sample plinninger 2010 the los angeles abrasion value test examines the resistance to degradation of bound aggregates in highway pavements a sample of coarse aggregate retained by a no 12 1 7 mm mesh sieve is weighed and is then subjected to abrasion and grinding in a steel drum the sample material is once again passed over a no 12 sieve and weighed the difference between the two weights is a measure of |
susceptibility to abrasion and therefore of the performance of the aggregate when subjected to abrasion during use abrasion is important in wind water and glacial erosion but it is also significant for determining the suitability of minerals for use as industrial and domestic abrasives blunting and wear on machinery such as that used in drilling and tunneling and the performance of aggregates during wear tests relate to the determination of hardness by scratching or by rebound on hammering or abrading samples to determine the rate of wearing down acid mine drainage is water encountered in and or draining from active or abandoned mines which has a low ph and or highly elevated concentrations of potentially ecotoxic metals mining disrupts the natural hydrogeological conditions in the subsurface often increasing the through flow of aerated waters resulting in oxidative dissolution of sulfide minerals the ferrous sulfide fes2 minerals pyrite and its less common polymorph marcasite release acidity when they dissolve this is not true of the non ferrous sulfide minerals this acidity can attack other minerals releasing further metals to solution clay minerals commonly dissolve to release al3 with mn2 zn2 and less commonly ni2 cu2 cd2 pb2 and the metalloid as also being mobilized where mineralogical sources for these are present above the water line dissolution is often incomplete and the products of sulfide oxidation accumulate as efflorescent hydroxysulfate minerals later dissolution of these will release acidity the resultant water is acid mine drainage albeit acidic is more correct in addition to low ph and elevated concentrations of iron and possibly other metals acid mine drainage is invariably rich in sulfate the total acidity in mine drainage has two components proton acidity due to the presence of high concentrations of hydrogen ions h that manifest in a low ph below 6 would typically be regarded as acidic in this context and metal acidity due to the presence of the metals listed above that tend to react with any available alkalinity to form hydroxide minerals releasing further protons in the process in many mine waters the total acidity is exceeded by the total alkalinity which in the relevant ph range is predominantly accounted for by dissolved bicarbonate hco3 such mine waters are termed net alkaline where the total acidity exceeds the total alkalinity the mine water is termed net acidic this distinction is important many net acidic mine waters actually have a near neutral ph 6 where they first flow out at surface but after prolonged oxidation and hydrolysis of their metal acidity ph drops to strongly acidic levels 4 5 misidentification of net acidic waters as net alkaline on the basis of ph alone can be a costly mistake the principal concern with acid mine drainage is ecological as it often devastates aquatic life in receiving watercourses in engi |
neering terms the high acidity poses heightened risks of corrosion of steel and other materials thus demanding careful galvanic protection the high sulfate concentrations pose a risk of rapid weathering of concretes based on ordinary portland cement sulfate resistant cements must be specified for structures likely to contact acid mine drainage acidic attack can weaken many rocks and engineering soils passive and active treatment methods are routinely used to treat acid mine drainage acidity ph is numerically equal to the negative decimal logarithm of the activity of ah or the concentration h of hydrogen ions in gram ions per liter this concept was introduced in 1909 by the danish chemist s rensen ph reflects the first letters of latin words potentia hydrogeni the power of hydrogen or pondus hydrogenii weight of hydrogen for low mineralized water the difference between activity and concentration of hydrogen ions is not geochemically significant but for high mineralized water the identification of activity and concentration is essential the introduction of ph as an indicator of acid base properties of aqueous solutions was founded on the ability of water to dissociate into ions according to the scheme h2o h oh in connection with this reaction and using the concept of ionic product of water kw ah aoh where kw ionic product of water ah and aoh activities of h and oh respectively kw at 22 c is equal 10 14 if the water does not contain other ions the h and oh concentrations are equal according to the electroneutrality of ion activities and at 22 c it has the value of 10 7 in that condition ph poh 7 the neutral reaction medium if h oh the solution is acidic ph 7 if h oh the solution is alkaline ph 7 the ph value is an important characteristic of all aqueous solutions and natural water bodies rivers lakes seas oceans the ph value along with the reduction oxidation redox potential determines the possible concentration in aqueous solutions of different chemical elements their migration forms and possible processes of changes of concentrations and properties of compounds it also has effects on soils and ecosystems both terrestrial and aquatic aeolian processes are processes related to wind in the atmosphere for engineering geology those processes which interact with the geosphere wind erodes transports and deposits materials especially in arid or semiarid areas with sparse vegetation cover and little soil moisture particularly where the substrate consists of unconsolidated sediments turbulent wind removes loose fine grained particles and entrains them as dust deflation or wears down surfaces by inter particle grinding and blasting or onto rock surfaces abrasion thereby creating more transportable material areas of long term sediment deflation result in a rock surface desert pavement deflation can form basin shaped depressions from centime |
tres to kilometres blowouts in size particles are transported in three different ways upwelling currents of air support small suspended particles less than 2 mm in diameter and can hold them in suspension indefinitely as haze or dust depending on how much is entrained sand sized particles can bounce some 1 cm above the ground surface at about half to one third of the wind speed saltation saltating particles can impact other grains that also saltate larger grains too heavy to saltate may be pushed rolled or slide creeping along surfaces aeolian turbidity currents arise when rain passes into arid areas causing cooler denser air to sink towards the ground when this reaches the ground it is deflected forward as wind and suspends mainly silt sized debris as dust storms suspension persists until the wind energy decreases and cannot support the weight of particles which are then deposited deposition is local if the particles are entrained near the ground and wind energy is low but dust can be transported for long distances in strong winds before deposition takes place if upwelling is strong enough to carry particles high into the atmosphere these can be distributed on the continental or global scale dust may be deposited sparsely into local soils but where frequent winds carrying large amounts of dust meet a barrier such as a mountain range thick silt deposits loess accumulate these are highly porous and have problematic engineering properties including compaction and collapse when moistened or affected by earthquakes wind across a loose dry surface moves and deposits particles locally wind over a sand grade surface may cause saltation forming troughs and crests with long axes perpendicular to the wind direction at distances wavelengths reflecting the average length of particle bounces the resulting ripples have the coarser material at the crests and finer material in the troughs larger scale movements build dunes by saltation and creep grains move up a slope towards a crest accumulate there and when the critical angle of repose is exceeded fall down the far side this angle is the steepest angle of dip to the horizontal plane to which a material can accrete without failing this causes a profile with a shallow back slope often covered with smaller ripples and a steep fore slope slip face nishimori and ouchi 1993 this repeated process causes slow advance of the dune until it is stabilized by changing climate and or armouring natural vegetation engineered surfaces dunes may sometimes grow to a few 100 m in height the characteristics of depositional structures are environmental indicators in the geological record wind has similar effects at a smaller and more local scale on dry uncohesive soils exposed by human activity such as sites stripped for quarrying construction and engineering works mine and quarry tips and tailings lagoons and ground cleared for agriculture leading to soil l |
oss and deterioration dust emissions can be reduced by keeping exposed surfaces moist or stabilizing them and enclosing plant and equipment aeolian processes can be relevant to engineering geology and engineering geologists in several ways the difficult site investigation and sampling conditions where dry poorly consolidated sand or silt deposits occur at the ground surface the need for careful support of excavations and trenches and design of appropriate foundations in poorly consolidated aeolian deposits the potential for collapse of loess when affected by earthquakes or excessive moisture the avoidance of dust emissions from construction mining and quarrying sites the analysis for potentially hazardous minerals and elements in dust the protection of developments from incursions of aeolian deposits aerial photography is an image of the ground produced on light sensitive media including digital sensors or a film of light sensitive emulsion that has been taken from an elevated position unsupported by a ground based structure aerial photographs may be vertical 3 from the camera to the focal point of the image or oblique vertical air photographs are those taken looking straight down they are typically used for mapping and photointerpretation oblique refers to photographs taken at an angle to the earth surface orthorectified orthophotos vertical air photographs taken looking straight down apparently from an infinite distance and where perspective and terrain corrections have been geometrically rectified such that the image may be viewed as a map film types film types most commonly used in aerial photography are black and white color and near infrared black and white images were common in the 1970s but largely overtaken by color images near infrared aerial photography is taken where the film or sensor is sensitive to the near infrared spectrum 700 900 nm it is frequently used to identify vegetative health and to reduce the effects of haze infrared photography is often called false color photography the ability to view the earth from a distance to observe landforms patterns sources of change the propagation of processes through a geomorphological system for example and evidence for geological history are largely attributable to the invention development of and improvements to aerial photography air photographs provided foundational knowledge upon which modern engineering geology is based they contributed to many aspects of the field from basic cartographic mapping to the slow unveiling of geological solutions that changed our perception of fundamental principles such as the scablands example provided below topography engineering geology relies substantially on understanding the topographic ground surface before aerial photography important ground features were sketched or surveyed post wwii however the widespread use of stereo air photographs allowed for the creation of nationwide accura |
te topographic maps using a stereoplotter a mapper would float a red dot along the surface of the ground as viewed through two air photographs the red dot could then be moved along x and y axes following the ground contour while remaining at the same elevation tracing this dot led to the creation of contour lines and ultimately topographic maps all of north america was mapped in this fashion the usa having complete topographic coverage at 1 24 000 and canada at 1 50 000 today topography can be created from overlapping images both oblique and vertical using the same principles partially or fully automated by computers the forefront of this technology allows the user to take multiple overlapping images from a regular camera or even a phone and create a three dimensional model of the image see structure from motion below direct mapping geological data that impacts engineering design is routinely derived from air photographs structural features such as joints faults folds bedding planes and other lineaments are often discernable from detailed and even regional imagery constraint maps might include information about wetlands karst activity depth to bedrock and the various types of ground instability e g fig 3 and important resources such as aggregate are also readily found on air photographs direct mapping is used to support and extend the information found in borehole investigations for foundations or for linear infrastructure resources and land use change it would be hard to overestimate the contribution of aerial photography to the understanding and development of national resources in canada for example where population densities are low the historical record of timber resources agricultural land and changes in land use were accurately captured by repeated air photograph surveys much of the country is covered at intervals of 10 years or less beginning in the mid 1950s similarly changes in coastlines the widespread existence of permafrost the ongoing movements of rivers and the development of transportation corridors pipeline routes and transmission lines all benefited enormously from the air photograph record geomorphological and terrain maps historically relied on air photographs to guide and direct engineering efforts with respect to hazards unravelling the scablands finally air photographs give engineering geologists new insights into old problems the scablands are an excellent example in the 1920s geologists had firmly adopted the theory of uniformitarianism the notion that the surface of the earth s crust has developed because of uniform and continuous processes throughout geological history harlen bretz 1923 examined the massive rock cut channels and huge ripples in east central washington and proposed something different in what he named the channeled scablands bretz proposed a post glacial flood of such magnitude that it was not accepted by his colleagues not only did bret |
z s theories contradict uniformitarianism but others argued that no sufficient source of water was available in 1956 bretz published results from a second field trip this time including air photographs showing massive ripple beds tens of meters high that began to turn the tide of criticism that had marred his work to date although it would be another 20 years before his ideas were fully accepted air photographs were fundamental in the visualization of the processes and to find adequate sources of water to create the landforms an aeromagnetic survey ams is an airborne geophysical survey performed using a magnetometer aboard or towed behind an aircraft a magnetometer is an instrument used to measure the magnetic field aeromagnetic surveys are probably one of the most common types of airborne geophysical surveys the applications of ams in engineering geology include but are not limited to near surface geological mapping structural geology mapping aiding three dimensional 3d geological subsurface model construction groundwater study environmental study and geologic hazards assessment in an aeromagnetic survey an airplane flying at a low altitude carrying a magnetic sensor flies back and forth in a grid like pattern over an area recording disturbances in the magnetic field fig 1 height and grid line spacing determine the resolution of the data geologic processes often bring together rocks with slightly different magnetic properties and these variations cause very small magnetic fields above the earth s surface the differences in the magnetic field are called anomalies rocks or soils containing iron and nickel can have strong magnetization and as a result can produce significant local magnetic fields the magnetic minerals contain various combinations of induced and remanent magnetization at exploration depths the earth s primary magnetic field is perturbed by the presence of magnetic iron oxide magnetite the most strongly magnetic and the most common magnetic mineral iron titanium oxides titanomagnetite titanomaghemite and titanohematite and iron sulfides pyrrhotite and greigite reynolds et al 1990 the remanent magnetization in the earth s magnetic field occurred during the mineral formation process whereas the induced magnetization was created by the presence of the earth s magnetic field the magnitudes of both induced and remanent magnetizations depend on the quantity composition and size of the magnetic mineral grains the goal of the magnetic method is to map changes in the magnetization that are in turn related to the distribution of magnetic minerals hoover et al 1992 magnetic measurements are usually made from low flying airplanes flying along closely spaced parallel flight lines additional flight lines are flown in the perpendicular direction to assist in data processing these large volumes of measurements are processed into a digital aeromagnetic map assisted by computer |
programs the geophysicist builds a geologic interpretation from the digital aeromagnetic data incorporating geological mapping and other geophysical information gravity seismic reflection where available fig 2 interpretations often involve both map based information e g a fault map and three dimensional information e g a geologic cross section and 3d geological model the workflow of the aeromagnetic survey method includes the aeromagnetic survey design data acquisition data processing and interpretation there are many parameters to consider in a typical aeromagnetic survey design these parameters include the line spacing of flying flying heights the flight line direction with the intention of maximizing the magnetic signature and features of the survey aircraft flight line spacing is determined by the degree of detail required in the final mapping or the size of exploration target and the funding available for the survey the strength of a magnetic field decreases approximately as the inverse of the square of the distance from the magnetic source therefore to record small variations in the fields aircraft must fly close to the ground as the aircraft flies the magnetometer measures and records the total intensity of the magnetic field at the sensor aeromagnetic data can be presented as contour plots or thematic maps e g fig 3 intensity of the aeromagnetic anomalies is expressed in these plots or maps as contour lines or different colors the shape depth and properties of the rock bodies causing the aeromagnetic anomalies can be interpreted by a trained geophysicist the magnetic anomaly map also allows a visualization of the geological structure of the upper crust in the subsurface particularly the spatial geometry of bodies of rock and the presence of faults and folds because different rock types differ in their content of magnetic minerals even if the bedrock is obscured by surficial materials such as sand soil or water aggregate is granular material such as sand gravel or crushed stone used for a variety of purposes but most commonly in relation to construction activities natural aggregates sand and gravel occur in various deposits reflecting different processes of erosion transportation abrasion and deposition often representative of local regional lithologies and all textural classes the most common aggregate rich environments are fluvial and glacial deposits but coastal marine desert and other environments can also be exploited in a fluvial environment fine grained aggregates are more common in meandering river and distal high energy streams conditions whereas coarser aggregates occur in proximal high energy or braided stream conditions glacial environments are by nature more variable in sand and gravel composition but somewhat more predictable when relying on facies analysis and sequence stratigraphy e g glaciofluvial deposits crushed stone aggregate is typically deriv |
ed at a local scale when natural aggregate is unavailable and is largely dependent on the bedrock lithology of the region most crushed aggregate is produced for concrete and road construction purposes most igneous rocks like dolerite and sedimentary rocks such as limestone and dolomite are excellent sources for crushed aggregate metamorphic rocks especially those with high cleavage and schistosity are a poor source for aggregate langer 1993 depending on the final purpose and use raw aggregate is processed in a number of ways including washing removal of detrital items sorting screening sieving etc the rock type shape and texture of aggregate strongly influence the range of uses for the materials for concrete and bituminous needs key properties of aggregate include hardness strength chemical properties size gradation particle shape contaminant absence specific gravity and so on aggregate is primarily used in construction activities but include a number of uses such as concrete cement and blocks road asphalt construction fill road subgrade bricks pipes roof shingles railroad ballast glass abrasives filtration beds fertilizer lime metallurgic fluxstone and so on the properties of aggregate are critically restrictive for certain uses and are subject to a suite of tests and technical specifications before adoption in some cases slag and clinkers are used as aggregate substitutes langer 1993 natural aggregate is typically mined through open pit operations or by dredging in water related environments crushed stone aggregate mining is commonly achieved by open pit or bank quarrying aggregate tests are tests performed on granular material such as sand gravel or crushed stone to determine their composition characteristics properties and suitability for specific uses natural and crushed stone aggregate serves a wide list of needs and uses around the world most aggregate is for construction purposes and of this most is used in portland cement concrete and bituminous mixes specific uses require specific requirements and attributes for the materials in use cement aggregate needs are more rigid and less flexible than for instance bituminous needs to ensure the most appropriate aggregate is used for a specific need a suite of tests are available to assess the composition characteristics properties and suitability of the aggregate materials the most common tests include abrasion test determines the hardness properties of aggregate most commonly relies on the los angeles abrasion test to establish the percentage of wear resulting from the rubbing action of steel balls abrasive charge on the aggregate samples cast iron spherical balls 48 mm in diameter 400 g are placed in a drum with 5 10 kg of aggregate after 500 to 1000 revolutions 30 rpm the sample is sieved weighed and compared to the total sample weight to provide a los angeles abrasion index bitumen adhesion test a n |
umber of tests are available to determine the reliability of adhesion of a bitumen binder to aggregate when water is present adhesion and binder stripping problems tend to arise when the bitumen mixture is permeable to water or the aggregate is exposed to wet and cold crushing test provides an indication of aggregate resistance to crushing under an applied crushing load the test requires samples of the aggregate to be subjected to standard load crushing conditions multiple layers of presieved materials are tamped 25 times before a 40 ton load is applied at a rate of 4 tons per minute the crushed aggregate is then sieved weighed and compared to the original total weight to provide an aggregate crushing value impact test determines the resistance of aggregates to impact forces multiple layers of sieved samples are tamped 25 times before a 14 kg hammer is dropped for a total of 15 blows the resultant sample is sieved and the weight is compared to the original sample to generate an impact value shape test this test provides an indication of the extent of detrimental flaky and elongated materials in the aggregate samples a flakiness gauge is used to define the percentage of particles whose smallest dimension is less than 6 10ths the mean size by weight an elongation gauge is used to define the percentage of particles whose longest dimension is 1 8 times the mean dimension by weight soundness test establishes the resistance of aggregate materials to prolonged weathering action sorted aggregate samples are subjected to 5 cycles of wetting saturated solution of sodium sulfate or magnesium sulfate and drying 105 110 c the weight loss in the sample provides a proxy indication of the disintegration potential of the materials specific gravity water absorption tests involve two measures of specific gravity apparent specific gravity and bulk specific gravity the former determines sg of aggregate minus voids and the latter sg of aggregate sample including the voids the water absorption test is simply the difference between the two measures of specific gravity extensive testing can involve any combination of the following assessments aggregate crushing value bulk density chloride sulfate content clay and fine silt color flakiness index los angeles value mean least dimension organic impurities particle density water absorption particle shape particle size distribution petrographic examination polished aggregate friction value resistance to stripping resistance to wear sieve analysis soundness unconfined compressive strength weak particles and wet dry strength variation alkali silica reaction is the reaction between alkali in cement and noncrystalline or porous silica in aggregate in the presence of moisture that may cause expansion and cracking of concrete alkali silica reaction asr is an acid base reaction between calcium hydroxide portlandite ca oh 2 and silicic acid h4sio4 the alkal |
ine solution reacts with amorphous silica to produce a viscous alkali silicate gel as the reaction proceeds ca2 ions are dissolved into the pore water these react with the gel to form solid calcium silicate hydrate whereas the alkaline solution converts the remaining siliceous minerals into bulky alkali silicate gel the increase in volume causes expansion pressure cracking and spalling that weakens the concrete and sometimes causes failure asr can be reduced or prevented by limiting silicate content of the aggregate by avoiding crushed rock or natural gravels containing amorphous or porous silica limiting the alkali metal content of the cement or preventing alkalis from external sources coming into contact adding fine grained siliceous materials as the cement is setting to promote a controlled reaction neutralizing excessive alkalinity a wide variety of rocks show alkali silica reactivity depending on the nature of contained silica including acidic and intermediate volcanic rocks obsidian rhyolite dacite andesite porphyries and tuffs granites and grano diorites shale slate sandstone siltstone quartzite siliceous carbonate rocks graywackes argillites chert and flint phyllites and granitic and grano dioritic gneisses suspect forms of silica are amorphous glasses and opal porous tridymite and cristobalite and microcrystalline chalcedony it is therefore important to carry out petrographical examination of potential aggregates and to undertake tests for potential alkali silica reactivity chemical methods crushed samples are reacted with 1 n sodium hydroxide at 80 c after 24 h the amount of silica dissolved from the aggregate and reduction in alkalinity of the solution are measured and plotted against a reference curve to establish whether these fall within one of three ranges innocuous deleterious or potentially deleterious the test identifies highly reactive aggregates fairly well but not slowly reactive aggregates and is helpful rather than reliable bar methods mortar bars are immersed in naoh solutions for 14 days or longer and changes in length are measured this is useful for aggregates that react slowly or expand late in the reaction however test conditions do not correspond to those of concrete in service and tend to overestimate aggregate reactivity the test indicates aggregates that are acceptable but not necessarily those that should be rejected alteration is any mineralogic change to a preexisting rock through chemical reaction caused by hot circulating hydrothermal fluids hydrothermal fluids owing to temperature and pressure gradient travel within a rock s primary or secondary porosity they react with country rock alter original mineralogy and produce new minerals hydrothermal fluids can be magmatic meteoric marine or sedimentary connate in origin they carry mobile elements large ion lithophile elements li be b rd cs alkalies alkali earths and volatiles th |
e fluids responsible for inducing alteration of minerals may eventually deposit ore minerals as a result of thermal and chemical changes therefore mapping alteration halos is key to discovering hydrothermal mineral deposits that may or may not outcrop on the surface alteration is common with porphyry skarn and orogenic magmatic vein hosted low temperature epithermal volcanic massive sulfide deposits alteration associated with magmatic and sedimentary hosted deposits does exist but is not very conspicuous common alteration reactions include hydrolysis a reaction between silicate minerals and either pure water or aqueous solution hydration addition of water to produce a new mineral dehydration carbonitization addition of co2 to form carbonate rocks decarbonitization removal of co2 from minerals alkali alkali earth replacement addition of alkali or alkaline earth metals silication replacement or breakdown of silicate minerals by reaction with free silica silicification hydrothermal alteration in which quartz opal chalcedony jasper or other forms of the amorphous silica content of the rock increase and oxidation addition of oxygen reduction removal of oxygen depending on the chemistry of hydrothermal fluids and the wall rock various assemblages of alteration mineral products may result the most common assemblages include potassic e g k feldspar biotite propylitic e g chlorite epidote calcite phyllic e g sericite and argillic kaolinite montmorillonite minerals alteration indices are used to discriminate altered rocks from their unaltered counterparts and to quantify the degree of alteration the common alteration indices include the hashimoto ishikawa acnk silicification and chlorite carbonate pyrite indices the angle of internal friction is a physical property of earth materials or the slope of a linear representation of the shear strength of earth materials earth materials that are unconsolidated and uncemented typically are called soil by engineers and geologists and may be called sediment by geologists soil consists of grains of minerals or rock fragments in a range of sizes mm to m from very fine to very coarse clay silt sand gravel cobble and boulder size grains that are chemically and mechanically separate from each other form a mass that can be excavated with relative ease and the excavated material can be placed in a pile that attains a conical shape with slopes that are at the angle of repose fig 1 the angle of repose is a representation of the angle of internal friction however it tends to be governed by grain shape such that the slopes of most piles of loose dry grains of natural soil are in the range of 28 to 34 a pile of angular gravel size grains can attain stable slope angles up to 45 shear strength of most soil is a function of the confining stress or normal stress nr such that it is lower at low normal stress and higher at high normal |
stress samples of alluvial silty medium to coarse sand subjected to direct shear testing might have a linear regression peak shear strength represented by eq 1 eq 1 describes an angle of internal friction of 33 5 and a cohesion intercept of 37 15 kpa a silty medium to coarse sand with nonplastic silt would be cohesionless a two parameter power function regression eq 2 of the same direct shear test data shows a variable angle of internal friction and forces the cohesion intercept to zero fig 2 which is appropriate for sandy soil the friction angle for the power function regression equation matches the linear regression at a normal stress value of approximately 118 kpa however the cohesion intercept for the tangent to the power function regression at this normal stress is 44 11 kpa earth materials are known to exhibit nonlinear strength and deformation behavior this example demonstrates the nonlinear strength aspect the shape of the coarse sand grains creates an equivalent roughness in the sample and is responsible for much of the nonlinear character in its shear strength the angle of internal friction is determined in a laboratory environment using a direct shear test or triaxial compression test theoretically the maximum angle at which grains in a heap of sediment can remain in place without becoming unstable the angle of repose of granular materials is relevant in various applications of science and engineering such as sedimentology geomorphology hydraulic and chemical engineering it can be used in the descriptions of initial motion of sediment grains and sediment transport process and in the investigations of bank stability riprap protection and reservoir sediment removal the angle of repose is measured using different methodstwo different slopes can be differentiated during the pile formation as grains are gradually added to a heap they can pile up to an upper angle of repose once masses slump a new surface will form at a lower angle of repose as a result the angle of repose varies repeatedly during the growth of the pile the upper angle is associated with the onset of slope instability and the lower angle is associated with the cessation of slope instability the upper angle of repose may also be measured as a critical angle using a tilting box for which some grains start to roll down along the inclined surface fig 2 in comparison the lower angle of repose is achieved at the end of an avalanche which can be generated by the removal of support for loose material fig 3 the angle of repose can also be measured by draining grains through a bottom opening of a container by building up a cone over a fixed base a rotating drum can be used to measure three different angles of repose fig 4 when the drum rotates a series of variations can be observed in the slope of the free surface of grains at a very low rotating speed grains move together with the drum demonstrating a rigid body |
motion until the slope reaches its upper angle then an increase in the slope angle triggers an avalanche transporting grains down the slope at the end of the avalanche a new slope forms at a lower angle if the rotating speed is increased both upper and lower angles disappear and the slope angle approaches a constant as grains keep rolling down the slope this indicates the beginning of the rolling stage the corresponding slope angle is referred to as the dynamic angle of repose at this stage grains move continuously from the upper to lower end of the slope yielding a surface shear layer of grains that flow down the plane inclined at a fixed angle theoretically the angle of repose can be considered the maximum angle at which grains can remain in place without becoming unstable unfortunately confusions often exist in the differentiation among the different angles of repose and thus the use of the term of angle of repose in the literature for example simons and senturk 1992 stated that the angle of repose is the angle of slope formed by particulate material under the critical equilibrium condition of incipient sliding soulsby 1997 applied the term of the angle of final repose for the angle of the lee slopes of dunes and the angle of slope of the conical scour around a circular vertical pile which is observed at the end of avalanching garcia 2008 considered the angle of repose as a slope angle beyond which spontaneous failure of the slope occurs an early differentiation between the upper and lower angles of slope was made by bagnold 1966 who called the upper angle the apparent limiting static friction angle of initial yield and the lower angle the residual angle allen 1969 described the upper angle as the angle of initial yield and the lower angle as the residual angle after shearing carrigy 1970 noted that there is no agreement reached as to what angle should be measured francis 1986 indicated that some confusion exists in the precise meaning of the term angle of repose and a single angle of repose is inadequate to explain all observable characteristics of many scree slopes aquifer is a layer or a layered sequence of rock or sediment comprising one or more geological formations that can store and transmit significant quantities of water under an ordinary hydraulic gradient aquifer also includes the unsaturated part of the permeable material that is the part above the water table as well as the saturated part the sole saturated part of an aquifer or the part from the aquifer bottom to the water table is referred to as the effective aquifer the most important characteristics of aquifers are the storing capacity or capability to store water in the rock voids pores and fractures and the hydraulic conductivity which is the capability of water to move through the solid matrix the hydraulic conductivity derives from the interconnected pores of unconsolidated sediments sand and gravel or by the fra |
cture network of consolidated sedimentary sandstone limestone igneous and metamorphic rocks some materials such as clay can have a high porosity but the scarce interconnection between pores makes such clay rich rocks quite impermeable thus creating a confining layer regarding the confining layer those layers with lower hydraulic conductivity aquifers can be classified as either unconfined or confined unconfined aquifer also known as phreatic aquifer or water table aquifer is one where the water table occurs within the aquifer layer in this type of aquifer the upper limit of saturation the water table is at atmospheric pressure and at any depth below the water table the pressure is greater than the atmospheric pressure and at any point above the water table capillary zone the pressure is less than atmospheric pressure the hydraulic heads measured in wells in an unconfined aquifer define a potentiometric surface that coincides with the water table the upper limit of saturation in plan view the water table surface is a contour map showing a horizontal distribution of heads in the aquifer groundwater pathways are perpendicular to the contour lines in a confined aquifer the entire thickness of the aquifer layer is saturated and there is a confining layer at the top of the aquifer at any point in confined aquifers the water pressure is greater than atmospheric pressure consequently the water level in a monitoring well in a confined aquifer rises above the top of the aquifer fig 2 the hydraulic heads measured in wells in a confined aquifer define the potentiometric surface an imaginary surface that does not coincide with the physical top of the aquifer in some heterogeneous settings lenses layers of less conductive materials can occur above the water table infiltrating water can be held up by those layers that form the base of saturated perched zones known as perched aquifers fig 2 if the lens is extensive the body of perched water may be thick enough to allow a water supply well to be tapped without drilling deeper to the regional water table usually aquifers are recharged by meteoric water that is rainfall infiltrating into the ground in the recharge areas within the normal hydrological cycle less common aquifers can bear connate water that represents water trapped in the pores of a rock during formation of the rock coastal aquifers can be hydraulically connected with seawater when fresh groundwater approaches the coastline its flow can be hampered by sea water the fresh water seawater contact is made up of an interface or more exactly a progressive mixing zone whose position is determined by the difference in hydraulic load between the water table and the middle sea level this interface is a natural and dynamic balance over pumping of freshwater can lead to a progressive intrusion of seawater into freshwater aquifers causing salinization of potable freshwater supplies the thickness of fr |
eshwater topping the seawater can be computed by the ghyben herzberg equation an aquitard is a leaky confining bed that transmits water at a very slow rate to or from an adjacent aquifer due to the reduced hydraulic conductivity aquitards permit water to move through at very slow rate as compared to the adjacent aquifers in particular they permit the vertical upward or downward flow of water between underlying and overlying aquifers depending on the hydraulic gradient aquitards differ from aquicludes in that the latter prevent water transmission and can act as a barrier to regional groundwater flow aquitards may transmit quantities of water that are significant in terms of regional groundwater flow but from which negligible supplies of groundwater can be obtained examples of aquitards include fluvial glaciofluvial and lacustrine deposits or poorly fractured sedimentary and crystalline rock water flow through aquitards depends on the hydraulic conductivity and thickness of the aquitard as well as the head difference between the adjacent aquifers as a result of pumping or seasonal recharge the hydraulic heads and therefore the groundwater motion can change during these periods fig 1 when the aquifer underlying the aquitard is capable of exchanging water through the aquitard it is known as a semi confined aquifer armour stone is a general term used to refer to a range of natural and sometimes artificial stone applications used for wave protection of shorelines and erosion protection of streambanks from the eroding action of waves and flowing water as well as in retaining walls and slope buttressing related to construction some applications use armour stone to refer to boulder size blocks of durable natural rock material applications of armour stone commonly are in the form of revetments but can be of a variety of shapes and positions relative to the shorelines or channel banks such as used for breakwaters fig 1 groynes and blankets ccaa 2008 the armour stone can be blocks and fragments that range in sizes usually to a specified gradation that are dumped into place or they can be uniform blocks that are carefully stacked nrcs 2007 armour stone applications are designed for minimal maintenance consequently the durability of the stone fragments has high importance rmour stone material is selected for its size mass and durability and sometimes for its shape as is the case for stacked blocks armour stone is also called quarry stone because the sizes required must be extracted by blasting rock formations defects in the rock mass such as bedding joints faults and dykes must be characterized for evaluating the likely range of sizes of durable rock material that might be produced from a prospective quarry sandstone formations with shale partings tend to be less desirable for use as armour stone than thick bedded sandstone formations certain applications of armour stone such as around bridge piers |
in river channels where it may be called riprap may be exposed to forces of turbulent clear water flow with little suspended sediment other applications may be in a coastal environment and exposed to high energy waves on beaches composed of gravel and cobbles the high energy beach environment exposes armour stone blocks to abrasion and wear by attrition tests for durability of armour stone material range from simple tests such as wetting drying freezing thawing sodium sulfate soundness and slake durability to more elaborate tests developed for concrete aggregate such as los angeles abrasion that involves pounding by steel balls in a rotating drum armour stone is popularly used in landscape design as retaining walls and buttressing of slopes where erosion protection from waves or flowing water may not be primary artificial ground are areas in which anthropogenic activities have directly modified the landscape by deposition and associated excavation artificial ground generally refers to landforms and sediments deposited or excavated on or within the shallow ground surface but such modifications can also be created at deeper levels in the subsurface where they cross cut existing natural geological strata this novel sedimentary environment includes areas of the excavation transport and deposition of natural geological materials and the deposition of novel materials related to activities such as urban development mineral exploitation waste management and land reclamation anthropogenically induced deposition of natural sediments such as behind dams or erosion such as through deforestation is not considered as artificial ground humans have already modified more than 50 of the ice free land surface of the world but the distribution is uneven urban areas which form only about 1 3 of the land surface have extensive anthropogenic deposits associated with the development of the city landscape and infrastructure typically the need to rebuild cities is facilitated by building upon the debris of older constructions artificially increasing land levels and creating environments that potentially favor the preservation of earlier urban strata rural areas normally have much less artificial ground cover with much of the remaining land surface associated with agriculture or forestry with subordinate development of rural settlements transportation networks and mineral extraction sites the agricultural disturbance of soil horizons through ploughing and land improvement such as applications of fertilizers and land drainage is commonly excluded from most concepts of artificial ground as is the extensive trawling and dredging followed by resettling of sea bed sediments on continental shelves the modifications associated with artificial ground were initiated in many parts of the world thousands of years ago however first through the industrial revolution starting in the late eighteenth century in the uk and subsequently the |
global great acceleration of the mid twentieth century the rate of accumulation the extent of reach of such landscape modification and diversity of composition of the deposits have increased dramatically this contribution considers how this anthropogenic landscape is described and classified by geologists how such modified ground is characterized through site investigation the nature of hazards and resources associated with artificial ground and how engineering investigation design and construction can be used to manage risk in an engineering geology context highly variable artificial deposits are defined as engineering soils such deposits can be markedly heterogeneous in composition depth and geotechnical properties ranging from fine to coarse soils from very soft to hard cohesive soils and very loose to very dense noncohesive soils though commonly ungraded e g landfills there are circumstances where such deposits may be uniformly graded as part of the production process e g pulverized fuel ash waste road sub base producing homogeneous deposits fill is a general term commonly used in site investigations to describe artificial deposits it can be used to denote material used to infill a void or cavity or in the case of constructional fill material that is added on to the natural ground surface several schemes have evolved to provide a means of classifying fill into units with distinct characteristics as carried out for natural rocks and superficial deposits there are numerous geological approaches to the classification of artificially modified ground technogenic deposits peloggia et al 2014 occur as subaerial subaqueous and subterranean environments with distinctions in genesis composition and morphology into deposit types which include both entirely artificial deposits and natural deposits that have been anthropogenically modified or influenced the scheme of peloggia et al 2014 recognizes technogenic grounds that are classified into four main categories table 2 aggraded ground degraded ground modified ground and mixed ground each of which is subdivided into specific genetic types aggraded ground includes built up deposits made ground and infilled ground induced alluvial and colluvial deposits and remobilized deposits degraded ground includes induced erosion such as eroded slipped or sunken ground as well as excavated ground modified ground comprises chemically and mechanically modified soils worked ground ground artificially cut away or excavated quarries pits rail and road cuttings dredged channels etc made ground artificially deposited ground engineered fill flood defenses spoil heaps coastal reclamation fill offshore dumping grounds constructional fill or landraise etc infilled ground ground artificially cut away and later infilled back filled workings such as pits quarries opencast sites landfill sites landscaped ground extensively remodeled g |
round where it is impractical to delineate areas of worked ground and made ground within it housing estates or golf courses disturbed ground mineral workings where excavations and associated subsidence are complexly associated with each other collapsed bell pits shallow mine workings etc transportation routes in roads railways tunnels and most airports the amount of materials moved to form the infrastructure i e earthworks are typically far greater than the built structures such as the road surfaces rail lines in order to maintain even gradients many transportation routes involve local shifting of materials with excavation of cuttings and redeposition of the extracted geological materials as embankments or through construction of cut and cover tunnels requiring limited costly importation or exportation of deposits douglas and lawson 2001 earth movement required for road foundations and new urban construction is an average of 0 75 m depth modern roads commonly have a surface of asphalt concrete or road metal tar macadam blacktop about 5 cm thick resting upon a compacted base of sand gravel or crushed rock aggregate ballast during the era of steam locomotives railway lands both depots carriage works and track beds included much timber coal debris oils and solvents and so were prone to spontaneous combustion waters et al 1996 the rail tracks continue to be made of steel now mainly resting on concrete sleepers rather than traditional wooden ones resting in turn on a ballast base at least 0 3 m thick road construction in hilly areas can initiate debris slides and flows can cause erosion particularly through gully initiation or act as a focus for sediment accumulation tarolli and sofia 2016 in flat landscapes elevated road or rail embankments can significantly impact on natural flood patterns mineral extraction it is estimated globally that 57 gigatonnes douglas and lawson 2001 of industrial minerals including sand gravel clay metal ore coal etc and including spoil and tailings and waste were quarried or mined annually at the turn of the millennium these minerals are mainly extracted by either underground mining or surface opencast or strip mining underground mining tends to selectively extract only the workable mineral and is typically associated with low volumes of waste materials although colliery spoil is an extensive type of made ground commonly forming elevated heaps in many coalfields of europe and the eastern usa surface mining which has become volumetrically more important over recent decades can result in stripping of overburden to depths of tens of meters to access the resource and creates significantly more waste ford et al 2014 though much of the overburden is commonly reinstated into the excavated void douglas and lawson 2001 as infilled ground this is particularly the case for large coal opencast sites large aggregate pits located along floodplains |
for example in the uk lack sufficient waste materials to allow reinstatement and high water tables make them unsuitable as landfill locations so commonly remain as flooded workings following completion although there can be opportunities for restoration of margins to support some wildlife subsidence of up to 50 mm year and lowering of the water table can accompany mineral extraction particularly by underground mining tarolli and sofia 2016 landslides debris flows and rockfalls are enhanced too in areas of extensive surface mining both within the spoil debris and within adjacent natural deposits industrial development many heavy industries have generated waste products both as artificial deposits and also air and waterborne contamination iron works foundries and other metal smelters produce large quantities of slag sand ash and spent refractory materials with high concentrations of heavy metals coal burning power stations generate large quantities of pulverized fuel ash pfa asbestos wastes generated either by the production of asbestos or in wastes that contain those products are a potentially significant hazard similarly radioactive wastes generated from power military medicinal or scientific usage also produce highly hazardous wastes the chemical industry produces diverse acids adhesives cleaning agents cosmetics dyes explosives fertilizers food additives industrial gases paints pharmaceuticals pesticides petro chemicals plastics textiles and so on each with distinct waste products a significant recent development is of large underground storage facilities these have been developed for liquefied petroleum gas and compressed air energy storage whereas the subsurface is increasingly used as a source of geothermal energy and to provide long term burial of nuclear and other hazardous wastes water supplies and sewerage in order to provide adequate water supplies and power for modern urban conurbations and to supply agricultural schemes river systems have been converted into reservoirs through construction of dams and barrages urban centers include extensive utility pipelines supplying clean water and removing sewage many sewage works are located on gravel beds on floodplains with such treatment works generating solid sewage sludge in many agricultural areas more than 80 of catchment areas can be drained by surface ditches or subsurface pipes flood defenses and coastal reclamation schemes engineered structures are commonly constructed to provide coastal defenses to control erosion and to protect human habitations from tides and waves these can take the form of seawalls and levees to protect from wave induced erosion or high tides similarly the construction of groynes breakwaters and artificial headlands inhibits lateral transport of sediments and maintains shingle and sand beaches which in turn protect from storm waves and tidal surges extensive areas of artificial ground res |
ult from land reclamation from lakes and seas the generation of extensive agricultural land e g polderization in the netherlands typically creates little artificial deposits in contrast reclamation increases living space facilitates construction of industrial sites or to locate major airports e g the palm jumeirah dubai and chek lap kok island hong kong and involves the transport and deposition of vast quantities of rock sediment and soil warfare precautions against impacts of warfare can include construction of defensive structures the results of warfare include building debris associated with bomb damage which is often aggregated to form extensive and thick deposits e g the teufelsberg berlin high explosives first initiated significant landscape modification during wwi creating extensive cratering of the western front from persistent detonations leaving little or no original soil surface remaining undisturbed and undetonated ordnance as a significant hazard based on history desk study to provide planners and developers with an indication of the categories of artificial ground described above that may be present at a site and the broad makeup of human made deposits desk studies should be undertaken so that planners and developers are aware of the risks of difficult engineering ground conditions and the potential presence of toxic residues and explosive gases and can ensure that site investigations are designed to assess these problems current and former land use can often be determined through sequential study of detailed scales of topographical and geological maps and aerial photographs these indicate areas of made worked and infilled ground as geomorphological features that represent a topographic modification to the preexisting land surface the descriptions of certain land use types though not comprehensive are commonly provided on topographic maps or carried out as part of regional land use studies an understanding of the current or former land use may provide an indication of the broad nature of the associated deposits in areas of mineral workings mine plans may identify the location of potential shallow open workings and mine entrances and opencast completion plans may show the extent and depth of workings prior to subsequent backfill waters et al 1996 the nature composition and thickness of made ground can be assessed from a study of historical borehole and trial pit data however such data are used with the caveat that the site investigation data would have been collected prior to the intended development of the site and would not necessarily reflect what is currently present potential surface elevation changes subsequent to development may be estimated through interpolation of start height data published on the historical site investigation record compared with elevations from a modern digital terrain model dtm the dtm can also provide an accurate determination of the locati |
on and vertical scale of geomorphological features which can be attributed to specific land uses such as railway embankment or quarry excavation ground investigation techniques made ground is heterogeneous and can rapidly vary in composition both laterally and vertically in order to determine the nature of fill material it is necessary for an appropriate site investigation to be carried out the investigation of artificial ground is a specialist task and must be carried out in compliance with current best practice e g bs 5930 2015 bs 10175 2011 and with regard to the safety of site personnel and the public ground investigations should involve trial pits and boreholes trial pits are particularly useful as they allow large sections of the fill to be inspected standpipe piezometers sealed into boreholes should be employed to obtain information about water levels within the fill the ground investigation should assess geotechnical aspects of artificial ground and should consider investigation of other relevant factors which could in some situations include chemical attack on buried pipes and concrete gas generation combustibility and toxicity investigation of contaminated land to detect and evaluate the concentrations of types and levels of pollution generally involves the following nirei et al 2012 a drilling or trial pitting often on a regularly spaced grid pattern and evaluation of the extent of contamination on the basis of predictive models using probability or geostatistical methods and b taking and analyzing samples at prescribed depths however it may be beneficial to consider such drilling and sampling programs to be designed to take proper account of the sequence of deposition of materials as well as their physical characteristics nirei et al 2012 using one of the schemes outlined in classification schemes the identification of units within artificial ground can establish how pollutants may have entered migrated through and accumulated within these deposits nirei et al 2012 with variable fill small scale laboratory tests may be of limited use whereas a program of field tests can provide much important information the most useful tests on deep fills may be simply to monitor settlement rates of the fill by precise leveling stable benchmarks need to be established away from the filled ground so it is important that the boundaries of the filled area are established by borings and pitting geophysical surveying may be used to aid the design of the borehole or trench site investigation and as a means of interpolating between and extrapolating from available borehole trial pit data but not to replace such direct investigation techniques to map out the lateral extent and potentially thickness of artificial deposits electrical resistivity conductivity techniques surveyed on a grid basis have proved effective in locating anomalous zones associated with infilled voids or changes in groundw |
ater composition electromagnetic em data can show high electrical conductivity in the near subsurface relating to contaminant plumes associated with leakage from landfill sites waste dumps mine waste tips and industrial pollution it can also provide information on foundations archaeological structures and presence of certain artifacts urban demolition wastes may be distinguished from natural soils by elevated electrical conductivity values 150 s cm table 4 with differences to native soils attributed partly to the presence of artifacts which are virtually ubiquitous in soils in urban areas howard 2014 self spontaneous potential sp methods are useful in recognizing groundwater flow paths in artificial deposits including seeps in earth dams atterberg limits are water contents at which marked changes occur in the engineering behavior of fine grained soils fine grained soils consisting of particles smaller than 0 074 mm 200 sieve include silt and clay water content is the ratio of the weight of water to the weight of solids in a soil mass expressed as a percentage in order to standardize the test procedure for atterberg limits casagrande 1932 defined liquid limit as the water content at which a groove cut in a soil pat by a standard grooving tool will require 25 blows to close for 13 mm when the ll apparatus cup drops 10 mm on a hard rubber base fig 2 the standardized test requires testing five to six samples so that approximately half require fewer than 25 blows to close the groove for 13 mm and half need more than 25 blows and plotting water contents determined by oven drying the tested samples for 24 h at 105 c versus logarithm of the corresponding number of blows fig 3 where the resulting curve known as the flow curve crosses 25 blows the corresponding water content defines the liquid limit details of liquid limit apparatus grooving tool specifications sample preparation and test procedure can be found in american society for testing and materials astm method d 4318 astm 2010 the liquid limit values can range from zero to 1000 with most soils having ll values less than 100 plastic limit is the water content at which a thread of soil rolled gently on a frosted glass plate to 3 mm diameter crumbles into segments 3 mm 10 mm long fig 2 if the thread can be rolled to a diameter smaller than 3 mm the soil water content is more than the pl and it should be balled up and rolled again if the thread starts crumbling before it is 3 mm in diameter the soil is drier than the pl and the procedure should be repeated after adding more water to it since the pl test is somewhat arbitrary at least three trials are performed and the average value is reported astm method d 4318 astm 2010 provides details of the test procedure for the pl test the pl can range from zero to 100 with most soils having values less than 40 plasticity index pi is the numerical difference between ll and pl i |
t is one of the most important index properties of fine grained soils barton bandis criterion a series of rock joint behavior routines which briefly stated allow the shear strength and normal stiffness of rock joints to be estimated graphed and numerically modelled for instance in the computer code udec bb coupled behavior with deformation and changes in conductivity is also included a key aspect of the criterion is the quantitative characterization of the joint joints or joint sets in question in order to provide three simple items of input data these concern the joint surface roughness jrc joint roughness coefficient the joint wall compressive strength jcs joint compressive strength and an empirically derived estimate of the residual friction angle r these three parameters have typical ranges of values from jrc 0 to 20 smooth planar to very rough undulating jcs 10 to 200 mpa weak weathered to strong unweathered and r 20 to 35 strongly weathered to fresh unweathered each of these parameters can be obtained from simple inexpensive index tests or can be estimated by those with experience bearing capacity is the maximum stress or pressure that a footing can sustain without failure of the soil or rock that is supporting the footing bearing capacity is a function of the shear strength of the soil material or rock mass but it also depends on the size and shape of the footing and the thickness of soil or rock adjacent to and above the base of the footing bearing capacity is a soil structure interaction phenomenon typically it is associated with foundations of buildings which is the domain of structural and geotechnical engineers engineering geologists provide valuable site characterization details pertaining to the nature and uniformity or variability of subsurface earth materials as well as the geohazards that might affect site suitability or represent constraints that require design provisions or mitigation by ground improvement prior to construction for buildings supported on shallow foundations spread footings the weight of the building is calculated by the structural engineer and proportioned to the walls and columns that provide the structural support system for the building walls are supported by spread footings that extend under the entire length of the wall continuous spread footings columns are supported by isolated spread footings in some cases in which a shallow foundation are determined to be suitable for structural support but building performance needs to be enhanced for rare events such as earthquake shaking foundation systems may be enhanced by tying isolated spread footings together with grade beams grade beams are reinforced concrete elements that are not relied upon to contribute to vertical load bearing capacity of a building s foundation system but act as structural elements that add stiffness to transform isolated spread footings into a connected network of sp |
read footings in certain geologic settings for example holocene marine clay deposits or for very heavy foundation structural loads tall buildings or for facilities that generate strong ground vibrations reciprocating compressors shallow spread footings would have insufficient capacity or would result in intolerable settlement of the building because of consolidation of clayey earth materials deep foundations shafts or piles are used to transfer loads deeper into the soil profile to a strong layer or to a depth sufficient for the load to be distributed along the length of a shaft or pile deep foundations have bearing capacities which are derived mostly from friction or adhesion of soil along the sides of the foundation elements with typically small contribution of bearing at the ends of the shafts or tips of the piles geotechnical engineers use shape factors to account for the stress distribution differences associated with footings of different shapes that bear on soil layers that are suitable to support the structural loads shallow footings may be isolated or continuous for columns or walls and have widths that are designed for the bearing capacity of the soil the base of the shallow footing may bear on soil less than 1 m below the ground surface adjacent to the footing or it may be designed to bear on soil several meters below the ground surface the ultimate bearing capacity is the maximum load that can be applied on a footing of specified dimensions that approaches but does not exceed the calculated soil shear strength variabilities in soil properties across the footprint of a building and uncertainties of temporary loads caused by wind and earthquakes are managed with an engineering approach called factor of safety which is the ratio of the soil s shear strength to the expected stress transmitted to the soil at the base of the footing the geotechnical engineer s best estimate of soil shear strength is used with information from the structural engineer and footing shape factors and embedment depths to calculate the ultimate bearing capacity of the foundation soil the ultimate bearing capacity is divided by the factor of safety commonly 3 or higher for foundation engineering to calculate allowable bearing capacity three types of shallow bearing capacity failure can occur general shear failure local shear failure and punching shear failure foundation failures typically are rare but general shear failures fig 1 are relatively more common than the other types general shear failure results from development of a shear surface below the footing that extends to the ground surface and produces distinctive bulging of the soil local shear failure results from consolidation or compaction of soil under a footing in a way that a shear surface is well defined near the footing but shearing becomes distributed away from the footing bulging of soil on the ground adjacent to the footing is noticeable punching shear fa |
ilure results from a geotechnical condition of a relatively strong surface soil layer that forms a crust over a weak soil layer the structural load essentially pushes the footing and strong soil into the underlying weak soil layer causing consolidation or compaction of the weak soil without noticeable bulging at the ground one type of bearing capacity that involves rock materials is support of pillars in room and pillar mines such as used in some coal mines darling 2011 in these cases engineering geologists or geological or mining engineers measure in situ stresses and calculate lithostatic stress that would need to be carried by the pillars the rock comprising the floor of the mine would be the foundation material for the pillars that act as columns in the structural support system of the mine pillars that are too small in cross section area tend to have stress concentrations that exceed the strength of the rock in the pillar as well as exceed the bearing capacity of the rock in the mine floor in coal stratigraphy a common bottom to top sequence might be sandstone siltstone claystone shale coal sandstone the coal formation would comprise the pillars whereas the claystone shale would comprise the foundation material coal tends to be brittle with a relatively low poisson s ratio and claystone shale may be relatively weak particularly if it becomes saturated the concept of bedrock in geosciences has despite it s apparent simplicity and worldwide use different meanings accordingly to the different fields of activity in which it is applied thus all magmatic metamorphic or sedimentary rocks beside sedimentary soils older than about two million years exposed at the earth s surface outcrop or overlain by unconsolidated deposits form the bedrock of a region but sometimes a sedimentary layer from the quaternary period may be classified as bedrock if it was subjected to tectonic stress reflected in visible folds or faults and lithification it is appropriate to apply this second tectonic criterion in seismic regions where tectonic stress is still active in contrast unconsolidated quaternary deposits as alteration products of bedrock residual soils regoliths or saprolites are distributed over bedrock in different geomorphologic features and formations alluvial diluvial or colluvial and are defined as shallow or surficial deposits the basic distinction between bedrock and surficial deposits is applied in engineering geology when acquiring qualitative information regarding soil properties prior to the execution of geotechnical in situ or laboratory tests and is most relevant if we compare mechanical properties of soils of similar kinds for instance clay soils in bedrock formations e g terrace formations of the tertiary period tend to be normal to overconsolidated and have low compressibility in contrast to clay soils formed as surficial deposits e g alluvial plains of the quaternary period which are u |
sually underconsolidated with high or very high compressibility mineralogical components of rocks are altered and modified when exposed to earth surface conditions in response to different atmospheric agents and insolation that may result in the disaggregation physical weathering or the decomposition chemical weathering of the rock when these processes are assisted by biologic action they are called biological weathering organisms may alter rock by both mechanical and chemical actions the penetrating and expanding pressure of plant roots in cracks fractures pores and other discontinuities may cause the rupture and disaggregation of the rock if there are favorable conditions and the strength of the rock is lower than that applied by the roots fig 1 penetration and expansion of lichen thalli has a similar behavior to that of the roots since some thalli may expand up to 3900 per cent due to their high content of gelatine organic activity mainly caused by microscopic organisms as bacteria fungi lichens mosses algae etc and also by animals plays an important role in the decomposition of the rock attack is by chemical means with the segregation of compounds as co2 nitrates and organic acids as metabolic products resulting eventually in the total alteration of the rock and soil formation the presence of water is essential to enable the growth of microorganisms and plants production of co2 and organic acids and nitrification increase the dissolution capacity of soil water heavy metals copper and zinc or even metal alloys such as bronze may inhibit biological growth controlled blasting is the carefully designed and successive placement of explosives with timed sequences of detonations to safely excavate low tensile strength materials to a defined surface it may be utilized to conduct rapid removals of materials while minimizing the risk of varied adverse impacts blasting is an effective procedure because chemical energy of the explosives is rapidly used to perform work two techniques utilize this rapid energy release controlled blasting of low tensile strength materials rock and concrete to be fractured and displaced to more easily processed sizes and severance of metal frameworks which deploys linear shaped charges detonated at discrete locations allowing the framework to be dismantled and displaced the performance of blasting and the potential risk of adverse impacts for both of these techniques are determined by several parameters and confinement of the explosive charges is a major factor controlled blasting confines the charge to allow the rapid expansion of the detonation products gases to perform work severance of steel framing is conducted without confinement of the linear shaped charges this technique will not be further reviewed all uses of explosives must be carefully designed because blasting is inherently destructive and may adversely affect surrounding assets controlled blasting is e |
mployed since it is more rapid and cost effective than mechanical means of excavation or demolition the primary blasting impacts of air blast noise fly rock thrown projectiles underwater overpressure pressure wave passage through water and ground vibration are dependent upon the shot pattern parameters ambient geology and weather conditions and surrounding built environment there are several secondary impacts due to blasting blasting projects assess environmental impacts which in the blasting industry is considered to be only protecting the nearby public or structures there may be insufficient evaluation of other secondary impacts sensitive features of certain equipment within buildings or historic and archeological elements natural resources and induced geologic hazards natural resource impacts are those adversely acting upon flora and fauna that have commercial value or are threatened or endangered species in the usa natural resource impacts are often prescriptively assessed under environmental regulations several geologic hazards may be induced or triggered by the primary impacts of blasting or may result from the physically excavated or demolished removals these induced geologic hazards may include soil displacement toward the removed material slope instability karst collapse changes of the ground water flow and liquefaction lateral spreading any project which may involve blasting should assess whether any adverse impacts may occur before developing contract specifications owners need to be informed of the assessed risks from both primary and secondary blasting impacts borehole investigations are a method of study to investigate soils and rocks in the earth s subsurface by means of long and narrow holes drilled using a variety of specialized methods successful engineering works often benefit from a clear and better understanding of the nature of soil and rock below ground in the absence of extensive trenching and excavation and to complement non invasive geophysical exploration techniques borehole investigations can be carried out including the analysis and characterization of the soil and rock recovered such investigations allow the identification of the soils or rocks present as well as an understanding of their physical properties on the basis of field and laboratory tests borehole investigations allow practitioners to determine the nature and location of the different soil rock layers collect samples carry out in situ tests and permeability tests and if necessary install piezometers and other subsurface monitoring tools the location of the boreholes is chosen depending on the objective of the project and characteristics of the tests with due consideration to the type of works planned boreholes may be drilled by two primary systems percussion or rotary techniques the former relies on the use of a tool that advances with successive hitting movements driven by a hammer that is dropped |
with its energy transmitted by means of rods to a solid tool or hollow tube sampler placed at the bottom of the borehole this system which has advantages in unconsolidated soils silt sand and gravel usually takes longer and is more expensive than rotary drilling the rotary technique fig 1 is the most frequently used method for subsurface exploration a cutting tool is used to collect samples using a helical auger or drill bit that moves forward by means of a bit crown that is usually widea or diamond tipped in the case of auger drilling alternative methods are needed to obtain samples which is normally carried out discontinuously this technique is mainly used in uncemented soft to medium consistency soils or in rocks in rotary core drilling a rock cylinder referred to as core may be extracted as the drilling advances and stored in a pipe screwed to the crown which is called a core barrel this may be a simple tube or a rotating double tube in which the inner tube is mounted on bearings in the case of loose or very soft soils a simple tube must be used whereas a rotating double tube is preferable in all other cases a casing pipe is introduced into the borehole to prevent cave ins or stop water leaks the casing is telescopic and allows the insertion of the core barrel to continue drilling the exterior diameter of normalized boreholes ranges between 54 and 143 mm borehole investigations for different civil engineering works must be approved by local state agencies complying with requirements usually determined by astm standards or similar specifications samples are representative portions of the soil rock that are collected for visual examination or to conduct laboratory tests depending on the means of collection they may be classified as disturbed or undisturbed samples usda 2012 disturbed samples only preserve some of the soil rock properties in their natural state and are usually stored in bags or as core segments undisturbed samples preserve at least in theory the same properties as the in situ soil reflecting the soil rock characteristics in their natural state at the moment of collection and consequently their physical structure in order to undertake laboratory tests it is necessary to collect undisturbed samples which are obtained by means of core barrels from the boreholes once the core barrel has been extracted the core within is retrieved and placed in a core box after the collected core is laid out it is visually inspected and the recovery obtained is measured core samples must be placed in adequate core boxes made of wood or waxed cardboard maintaining the original position and orientation and indicating the depth for this operation to be properly carried out the same sequence in which the samples were obtained must be followed introducing separation blocks between the different core runs and defining sampling depths as well as the core recovery percentage the rock qualit |
y designation rqd of all the core samples obtained is determined deere and deere 1988 this index expressed as a percentage is defined as a quotient between the sum of the length of the core pieces and the total length of the core run there are different tools for the collection of samples and depending on their characteristics disturbed or undisturbed samples will be obtained the use of a shelby tube sampler is preferred in cohesive silty and clayey soils whereas a split spoon sampler is used in sandy soils small 2016 a sample extracted by means of a hand or machine driven auger consists of a short cylinder that is obtained from the combination of rotation and downward force samples collected in this manner are regarded as disturbed undisturbed soil samples may be collected by means of thin wall coring tubes that are pushed into the ground thick wall coring tubes are driven into the soil with a hammer in order to collect soil samples with some cohesion the sample within the tube is a representative sample but it is not considered undisturbed in order to avoid dropping the sample from the tube due to the thrust of water when operating below the water table a valve is located at the top of the sampler and it is seated on the head of the tube to prevent the water from descending and putting pressure on the sample it is a simple robust sampler whose greatest disadvantage is that the sample must be pushed to extract it from the tube which subjects it to a certain degree of deformation the shelby tube sampler is very simple and widely used it consists of a thin wall tube generally made of steel with a sharp cutting edge the disadvantage of this type of sampler is that it is necessary to push the sample out of the tube which causes some disturbance stationary piston samplers avoid the penetration of mud or prevent the water pressure from affecting the sample as water enters the tube and raises the ball when discharging the water towards the rods they may be used in soft to moderately stiff clayey soils and in loose sand a double tube soil core barrel has a core lifter that protrudes some 4 9 cm from the crown which ensures that the drilling fluid will not reach the sample and that the crown will not come into contact with the core it may be used in clayey soils of hard consistency and the quality of the samples obtained is regular to good depending on the ground conditions when the soils are cohesive and their resistance is high the collection of an undisturbed sample is substituted by dipping in paraffin the longest section of the core obtained these sections once they have been superficially cleaned must be covered in non absorbent material and everything must be protected with a paraffin wax seal thick enough to ensure there are no variations in the humidity conditions water samples are collected from boreholes to study the hydrochemical characteristics of the water found in the survey points it is |
common to keep a record of the water table level in every borehole fig 2 not only during the drilling but also once it has been completed at least until the end of the field work the main tests undertaken in situ in a borehole are as follows standard penetration test spt the spt is the most common test among those conducted within a borehole price 2009 it is a simple test and it may be performed while the borehole is being drilled it may be applied to any type of soil including soft or weathered rocks it is possible to correlate the spt with the mechanical soil parameters this correlation together with the data obtained from laboratory tests helps define the allowable pressure of a soil for a specific type of grouting the spt is an in situ dynamic penetration test designed to obtain information on the soil properties while it also collects a disturbed soil sample to analyze grain size and determine soil classification the spt n value is defined as the number of blows required to achieve a penetration of 45 cm with a sampler placed in the lower portion of the drive rods it is driven into the ground by means of a 63 5 kg 140 lb hammer that is dropped in free fall on the top end of the drive rods from a height of 76 cm 30 inches usually the sampler has an outside diameter of 2 inches and an inside diameter of 1 inches in the case of gravel a conical tip with a diameter of 2 inches and an apex angle of 60 is used as a hollow tool is used the test makes it possible to collect a disturbed sample of the soil in which the penetration test was carried out so as to analyze in the laboratory pressuremeter and dilatometer tests these are stress strain tests undertaken directly in the soil in order to identify its geotechnical characteristics regarding its deformability pressuremeter modulus and resistance properties limit pressure they are conducted by the expansion with gas of a cylinder cell against the walls of a borehole measuring the volumetric deformation of the soil in a horizontal plane corresponding to each pressure until eventually the soil yields regardless of the problem posed by the transformation of the results obtained in the horizontal measurements in the case of the reaction of the foundations which are usually vertical and of the fact that soils tend not to be isotropic but heterogeneous these tests provide isolated and therefore discontinuous data as regards the layers encountered the guidelines to conduct this test are set out in the astm d 4719 87 standard permeability tests in situ permeability tests are conducted in soils and rocks the most common ones consist of the addition or extraction of water under a constant or variable hydraulic head a reliable estimation of the permeability coefficient is possible in surveys that detect the occurrence of the water table and in boreholes in which this coefficient ranges from 10 3 to 10 5 cm s in the case of lower permeabilities it |
is necessary to resort to pumping or laboratory tests the most frequent ones are referred to as the lefranc and lugeon tests monnet 2015 the lefranc test is carried out within a borehole during the drilling or once it has been completed this test estimates the permeability coefficient k in granular soils gravel sand and silt or in highly fractured rocks occurring below the water table it is performed by filling the borehole with water and measuring the necessary flow to maintain a constant level constant head or the fall velocity variable head in the constant head test as a general rule the inflow rate is measured at specific time intervals keeping a constant level at the borehole head the k coefficient of the section is the average of all the values obtained the variable head test is preferably conducted downward starting from a maximum head of water and recording the decrease in water level within the pipe at different times the lugeon test consists of injecting water under pressure at an isolated section of a borehole bounded by one or two packers and measuring the amount of water that infiltrates into the soil this test can be carried out as the borehole is being drilled or once it is completed first the section to be tested is chosen once the packers are in place the injection of water begins measuring the volume of water injected the measurement is performed at certain intervals starting with a minimum pressure and increasing this in stages all the while measuring the volume of water intake starting from the maximum pressure the same process is repeated but decreasing the pressure at each stage until the initial pressure is reached water is injected by means of a pump measuring the pressure with a gauge and the volume injected with a flowmeter this test is applied to medium to low permeability consolidated soils or rocks 10 6 k 10 9 m s different tests can be performed in the laboratory which makes it possible to measure a wide variety of soil properties some of these properties are intrinsic to the composition of the soil matrix and they are not affected by the disturbance of the sample whereas other properties depend on the structure and composition of the soil and these can only be analyzed effectively in relatively undisturbed samples besides geologic logs from drill holes a suite of geophysical logs can be collected to provide additional information regarding the nature and distribution of materials below the ground surface typical data collected in this manner comprise spontaneous potential sp resistivity gamma ray gamma gamma radioactive neutron and other methods acoustic camera televiewer etc the direct study methods used in engineering geology are based on geotechnical surveys which allow for the sampling of subsurface materials and the undertaking of in situ tests boreholes are drilled by percussion or rotary techniques with the latter being the most common |
different types of tools are available to obtain disturbed and undisturbed samples undisturbed samples are those that best maintain the physical structure and properties of the soil and lead to more reliable laboratory test results tests undertaken in situ in a borehole include penetration tests pressuremeter and dilatometer tests and permeability tests all of these together with the ones performed in the laboratory on the samples obtained from the boreholes are essential to understand the characteristics of the soil and to design engineering works to be constructed at the study site boreholes are a narrow hole drilled to establish the nature of sample test or monitor soil bedrock or contained fluids and gases or for abstraction of water or minerals the borehole drilling system consists of a drill head which powers the operation a drill string which extends down the borehole and a drill bit which cuts through the substrate the drill string may be surrounded by a collar separated from the drill string by an annular space the annular space allows water or mud to be pumped down and for soil and cuttings to be flushed up to the ground surface the practical limits on the depth and rapidity with which a borehole can be drilled and the diameter of the bore is governed solely by the size and power of the rig used if a borehole is required for use over a period of time if it is into uncohesive deposits or if it is deep a lining or casing of plastic steel or iron is sunk to protect the hole from collapse the main techniques involved in the construction of boreholes icrc 2010 are percussion rotary and sonic light cable percussion technique also known as shell and auger this is a relatively quick and cheap method for drilling to depths up to about 60 m and to recover samples on the auger it is used extensively in civil engineering and shallow mineral deposit site investigations air percussion technique this technique of percussion drilling utilizes compressed air to operate a down hole air hammer on the end of the drill string that helps break the rock formation this borehole drilling mode always requires the skills of an expert the compressed air is usually used to operate an air hammer which is situated deep down the hole the rotary technique in rotary drilling a drill bit is attached to a length of connected drill pipe the drill bit is made of strong metals such as tungsten so that the rotating drill bit can easily grind the rock drill fluids sometimes referred to as drilling mud are circulated through the drill string into the borehole and back to the surface carrying flush the broken pieces cuttings of bedrock upwards and out of the hole this fluid also serves as a formation stabilizer preventing possible caving in of unstable sand or weak rock before the well casing or well screen can be installed furthermore this fluid acts as a drill bit lubricant as the drill intersects water bearing rock fo |
rmations water will eventually flow into the hole drillers or hydrogeologists on site will carefully monitor the depth of water strikes and keep a note of the formations in which they occur sonic drillingtechnique an oscillator in the drill head generates high frequency resonant energy which is directed down the drill string causing soils in a narrow zone between the string and head to lose structure and reduces friction so that soil or cuttings can be readily flushed away boreholes require sophisticated technology with the right appropriate technical design together with proper knowledge of the underlying target such as an aquifer or oil reservoir unfortunately the importance of good quality borehole design and construction is often underestimated the lifetime of a borehole and the efficiency of its functioning depend directly on the materials and the technology used borehole failure is often linked to incorrect design and construction of the hole constructing or repairing boreholes requires specialized knowledge and technical expertise much of which can be gained from the standard literature but field operations in remote areas or in difficult conditions often require flexibility and imagination in avoiding and solving technical problems during borehole drilling certain problems may be encountered azar and robello samuel 2007 the drill is expected to act moderately if pushed down excessively on the rock surface or rotated too quickly the drill bit may be destroyed on the other hand if the drilling does not produce enough force hard rock layers will not be penetrated caution may be needed if the top of bedrock or a competent layer needs to be identified e g prior to piling because drilling into large boulders might be mistaken for detecting the actual interface also drilling hazards may be encountered e g contaminants polluted water unexploded ordnance or natural gases or oil under high pressure problems may also arise if shallow drilling encounters voids such as natural caves or unrecorded mine cavities a variety of downhole tools are lowered into boreholes for testing and monitoring such as geophysical tools to investigate adjacent strata or to secure data to interpolate between groups of boreholes site investigations for construction projects or evaluation of potentially polluted or contaminated land mainly consist of relatively shallow drilling and sampling some holes are drilled and then made safe very quickly but others are kept open for monitoring of groundwater or gas emissions systematic site investigation requires boreholes to be drilled on a grid pattern with the initial spacing between boreholes being determined by the expected distribution of the ground characteristics that are being examined and new boreholes at different spacings being made if the need arises to investigate unexpected features deeper drilling is needed to investigate larger scale problems for instance to def |
ine the slip planes of landslides boreholes are also sunk for dewatering of excavations and draining water from landslides in boreholes for water supply the bottom section of the lining has slots to allow water to enter the borehole gravel is placed at the bottom of the lining to improve flow and provide filtration the design and construction of boreholes and wells for groundwater extraction is very technical and requires expert groundwater hydrologists and engineer when holes or wells are drilled for the purpose of evaluating the content of the hole as retrieved it is called exploration drilling annels 1991 mining companies utilize this type of drilling to retrieve mineral samples of a specific location for the purpose of evaluating the samples to determine whether the quality and quantity of a specific mineral are sufficient to make mining at the location viable reverse circulation is one method used and it entails retrieval of the drill cuttings using drill rods that are used for the transport path of the cuttings to the surface a hammer drives the tungsten steel drill point into the rock or soil with this method depths of up to 500 m can be drilled the retrieved material is dry odex and tricone systems are used in reverse circulation drilling with odex the hammer drill bit fits at the end of the steel casing and the hammer is used for crushing the material which is blown up into the casing where the retrieved cuttings are transported to the surface the system is used when there is a risk of rock collapsing in the drill area this is a time consuming and sometimes very expensive method but it is often the only type of method that can be used to prevent rockfalls the tricone system is used for water oil and petroleum retrieval it entails roller cone bits grouped into a drill bit that rotates into the rock formation it is a suitable method when the drill bits must be protected and when only a small sample of content has to be retrieved core drilling is normally used when faster exploration drilling is needed it can also be used in the construction sector for drilling pipe holes a borehole is drilled for extraction of minerals relying on a process that uses high pressure water the water jets make it possible to drill into hard rock whether in an open pit floor underground mine space land surface or from a vessel in the sea or on a lake the first step is to drill to the desired depth from the surface the next step is to lower a casing column into the well with the shoe of the casing situated above the top boundary of the productive mineral in the case of oil and gas extraction the fluid may initially rise to the surface through the borehole due to pressure but as time passes it becomes necessary to enhance recovery by fracturing the reservoir rocks blake 1979 in ore mining by borehole a third step involves the lowering of the borehole mining tool into the drill well pivnyak et al 2017 this method r |
equires less capital outlay than many other mining methods and it makes it possible to work in otherwise inaccessible areas that are too dangerous for conventional mining it has a relatively low environmental footprint and allows for better mobility when it comes to changing mining locations more selectivity can be applied meaning less wastage and higher profits the method is frequently used for mining minerals such as gold uranium diamonds coal and quartz sand it is also used for oil and gas extraction boreholes can also be used for solution mining where water is pumped in dissolves a mineral such as salt to form brine which is then recovered at the surface arrays of boreholes are drilled on a linear or grid pattern for the purpose of inserting charges for blasting to break up the mineral directional drilling is the drilling of oblique or horizontal boreholes azar and robello samuel 2007 it is used for a variety of purposes for instance in deep drilling for oil or natural gas a borehole is made at a single suitable location and is then used for drilling of a number of oblique borings to further investigate and exploit a reservoir which minimizes the number of well heads that affect the surface environment to reduce the pressure of a well in order to minimize the risk of a pressure blow out for hydraulic fracturing of oil shales to release the hydrocarbons or to exploit coal bed methane horizontal drilling for installation of utilities the costs of boreholes depends on the depth of drilling the diameter of the hole and the need for casing but it is also influenced significantly by the applied design as well as the difficulty to construct a borehole in certain geological formations stapenhurst 2009 it is fairly common for developers to try to reduce costs by not allowing for the insertion of casing or by reducing the number of boreholes that is needed to adequately investigate the problem in the short term these seem costly but almost always pay off in the long run thus casing will allow for the borehole to stay open for years after completion and if correctly installed it will also assist in keeping the borehole clean and free of material that could damage a borehole pump also an adequate number of boreholes in a construction site will normally avoid unexpected later costs for remedial works and delays to development it is important to have professionally competent specialists when designing undertaking and using boreholes brownfield sites are previously developed land that has become disused as opposed to greenfield sites those that have not had previous uses other than agriculture forestry or no perceptible human interventions brownfield sites are mainly located in urban areas where industrial or commercial buildings and facilities have become disused but some sites such as military installations mines and waste management sites may be located in open countryside or wilderness areas in |
dividual sites may cover many hectares or be small and scattered some can be easily redeveloped but many have problems of contamination pollution instability and obstructions from past uses that add to difficulties and costs of either redevelopment or rehabilitation surficial deposits on such sites are often of anthropogenic origin sites may be vacant i e essentially intact but not in use or derelict abandoned and in poor condition or may still be partly used e g a scrap yard on a former factory site contaminants in brownfield sites may include solids liquids and gases and volatile organic compounds the nature and composition of these depends on the various human activities that have taken place these may include hydrocarbons solvents pesticides potentially harmful elements and inorganic compounds phenols and related compounds cyanides and asbestos and sometimes radioactive materials or munitions some are toxic asphyxiant or carcinogenic others can react chemically with construction materials such as concrete and metal form work treatment of contamination traditionally involved excavation and removal to landfill commonly referred to as dig and dump while that is the least expensive option it simply moves contaminants from one place to another alternatives which are environmentally more sustainable but are also usually more expensive include soil washing excavation of soils and washing them using internally recycled water to avoid additional pollution and careful disposal of the resulting water in situ thermal desorption to mobilize volatile and semivolatile organic contaminants bioremediation phytoremediation breaking down contaminants using injected or bacteria or fungi or by using deep rooted plants to extract heavy metals and when fully grown to cut these and dispose of them to landfill in situ chemical oxidation injection of oxidants such as sodium or potassium permanganate ozone or fenton s reagent to treat or reduce the toxicity of certain organic contaminants e g benzene toluene and chlorinated solvents in situ soil vapor extraction use of vacuum blowers and extraction wells to induce gas flow through the subsurface so that it can be collected and treated aboveground previously used land sometimes contains cavities such as shallow mines cellars and storage tanks which may need to be excavated and or filled and shafts and wells that need to be capped or filled to ensure stability tipped materials that may be poorly consolidated and subject to settlement foundations of previous structures and services e g pipes and cables that may need to be excavated and removed many sites require demolition of buildings and foundations it is desirable to as far as possible recycle debris e g recovery of metals and soils crushing of concrete and masonry for use as aggregates however the components of old buildings may be difficult to separate economically and can be fu |
rther contaminated by materials such as asbestos in which case they must be landfilled as hazardous waste simplistically it might be thought that brownfield sites are environmentally undesirable and should be fully remediated to benefit the environment wildlife and people that is often true but there are important exceptions disturbed ground that is left vacant for a protracted period attracts plants that are adapted for invading such settings these form the basis of new ecosystems and can add to local biodiversity angold et al 2006 instances are known where deposits of particular chemical compositions have led to unusual plant communities on sites that were of sufficient interest for the sites to be given protected status therefore collaboration between engineering geologists and ecologists is important some previously used land may have gone through several rounds of development and abandonment over several hundred years the early stages of which may now be of archaeological industrial archaeological importance symonds 2010 these require collaboration between engineering geologists and archaeologists commonly the history of a site and consequent problems are not fully known therefore detailed site investigation is normally necessary to identify potential problems so that reliable cost estimates for remedial works can be made this can be time consuming and expensive investigations have five main elements examination of old maps documents publications and photographs to identify all previous uses of the site to establish which problems may have been inherited from these a walk over survey and mapping of the site to observe evidence of problems and potential advantages and to provide the context for ground investigations design of an investigation strategy site investigation trial pitting drilling geophysical survey sampling testing and monitoring preparation of a report setting out the steps and techniques that should be adopted during site remediation and development remediation of brownfield sites is usually more and sometimes prohibitively expensive than developing greenfield sites making these less attractive to developers but making use of brownfield sites is often needed to improve derelict land and minimize damage to undeveloped land de sousa 2000 in several countries the amounts and types of brownfield land are monitored together with progress on redevelopment in some cases registers are kept that developers can use to identify sites for possible redevelopment various measures have been developed to incentivize the re use of brownfield land for example collaborations between private companies and insurance companies to underwrite clean up guarantee clean up costs and limit the exposure of developers to environmental costs and litigation usa site assessment using public money to provide certainty to prospective developers usa tax incentives grants paid by government to of |
fset costs of remediation uk there have been two main philosophies for remediation to make the site safe for all possible subsequent uses some specific uses following remedial action the former is usually much more expensive so the latter is more often adopted building stone is a generic term referring to all naturally occurring rock natural stone as defined by bsi 2002 used in the building construction industry including a wide variety of igneous sedimentary and metamorphic rocks if after quarrying the rock has been selected and cut to specific sizes and shapes it is referred as dimension stone bulk modulus k is the ratio of hydrostatic stress p on an object to the resulting volumetric strain v which is the ratio of volume change v to the initial volume vo hydrostatic stress cannot produce shear stress however principal stress acting in one direction produces strain in all three directions as described by hooke s law and poisson s ratio bulk modulus can be calculated from two basic elastic properties young s modulus and poisson s ratio a singularity in k occurs at 0 5 which pertains to incompressible materials mott et al 2008 but is not relevant in real materials of interest to engineering geologists the california bearing ratio cbr is an index that compares penetration resistance of laboratory compacted soil material to that of a durable well graded poorly sorted crushed rock material it is a standard test with procedures specified by american association of state highway and transportation officials aashto 2013 and american society for testing and materials astm 2016 in north america the test uses a standard compaction mold with a diameter of 152 4 mm and a height of 177 8 mm the degree of compaction and range of moisture content are specified for the test depending on project requirements in most cases the sample is compacted into the mold and then submerged in water for 4 days prior to testing the sample and mold are removed from the water a ring shaped surcharge load is applied to the surface of the compacted soil in the mold and a load is applied to a steel piston that has a diameter of 49 6 mm to attain a penetration rate of 1 3 mm per minute the load at penetrations of 2 54 mm and 5 08 mm is recorded the recorded loads are converted to stress values by dividing the load by the area of the end of the steel piston these stress values are compared to the equivalent crushed rock standard stress values of 6 9 mpa for the 2 54 mm penetration and 10 3 mpa for the 5 08 mm penetration cbr is calculated as the average of the ratio of laboratory stress to standard stress for the two penetration depths expressed as a percentage fig 1 and referenced to an optimum water content and a specified dry unit weight which usually is given as a percentage of the maximum dry unit determined by a standard compaction test cambering occurs where competent and permeable caprock over |
lies incompetent beds e g clay mudstone siltstone and sand following valley incision the incompetent material is extruded from beneath the caprock initially as a result of stress relief and a reduction in shear strength due to pore pressure increases associated with thawing during periglaciation the overlying competent beds develop a local dip or camber toward the valleys and where relatively thin sets of cross slope subvertical parallel discontinuities may form commonly developing into faults separating more steeply dipping blocks referred to as dip and fault structure fig 1 chandler et al 1976 hutchinson 1991 with time this process breaks the caprock into discrete blocks floating in the medium of the underlying weaker strata under lateral extension the resulting inter block discontinuities open and these gulls tend to become at least partially filled with disturbed material from adjacent underlying and overlying strata the gulls may or may not be marked at the surface by topographic hollows ultimately the whole mass may be incorporated into landslides on the valley slope cambering is often associated with valley bulges and gull caves the former represents the uplift of the valley floor due to stress relief within incompetent strata e g due to rapid proglacial down cutting and the latter the later stages in the development of gulls within the caprock resulting in labyrinthine networks penetrating tens or even hundreds of meters from the valley side the need for engineering geologists to recognize the presence or likelihood of cambering is paramount so that potential geohazards are not missed suitable 3d engineering geological models should be produced these will tend to be more complex than an uncambered equivalent rock mass characteristics of caprock may require reappraisal effective investigation methods include geophysical techniques aerial lidar and traditional geological mapping with augers cap rock is the upper rock material that is more resistant to erosion than the underlying rock material it also refers to a sedimentary unit of lower hydraulic conductivity than that of the underlying oil or gas reservoir rock that restricts upward migration of hydrocarbons thus effectively capping the reservoir in geomorphology the upper rock material that is more resistant to erosion than the underlying rock material is called cap rock cap rock typically forms a distinctive ledge at the crest of an escarpment in petroleum geology in addition to a lower hydraulic conductivity sedimentary unit that restricts upward migration of hydrocarbons cap rock also forms above salt domes as a characteristic sequence of calcite anhydrite and gypsum that can exceed 300 m in thickness over the halite of the salt dome the upward movement of the salt dome deforms the overlying rock formation producing fractures into which the halite penetrates groundwater dissolves the upper surface of the intrud |
ing salt formation and any impurities in it producing the anhydrite and gypsum interaction of anhydrite and gypsum with bacterial activity can produce sulfur in the cap rock of salt domes sometimes in deposits of economic value for mining capillarity in soils refers to the upward flow of water above the groundwater table a casagrande test is a standard test to determine the liquid limit of a sample casing has many applications in engineering geology well and borehole casing is a steel tubular pipe installed underneath the ground surface to access extract and transport natural resources from deep formations pile casing can serve as a permanent structural member to resist and transfer vertical and horizontal loads from superstructure to founding soil or rock the term is also used in relation to pipelines but this entry focusses on wells boreholes and piles different well and borehole casings are specially designed installed and operated for various applications in the energy and environmental engineering sectors conventional well casings can be used to access and extract oil gas or water from deep reservoirs in some tight reservoirs where the permeability is in a range of nano darcies stimulation techniques such as hydraulic fracturing may be necessary to create new fractures or reactivate in situ natural fractures to increase the production rate in some reservoirs containing heavy oil and bitumen with high in situ viscosity in the range of 100 000 1 000 000 cp condensed steam is injected into the formation to lower the oil viscosity so that the fluid oil and water can be extracted butler 1991 such wells are also called thermal wells as they are subjected to high pressures in mpa and temperatures up to 300 c high temperatures and pressures are also encountered in casing wells that are used to extract geothermal energy from very deep formations by circulating cold water martinez garzon et al 2013 waste water produced from mining or oil extraction can be disposed of in certain contained formations typically a completed well comprises a series of annular rings of steel casing well cement and the surrounding geological formations of varying thickness fig 1 as part of well completion a borehole is drilled and then advanced with the aid of drilling mud to prevent potential borehole collapse then steel casings are inserted into the drilled hole and filled with mud the mud is injected into the annular space between the steel casing and the drilled hole and is removed by a clear wash or spacer fluid followed by injection of a cement slurry several casings are installed at multiple intervals to serve different functions starting from the well head at ground level a conductor casing is installed to provide support during drilling operations to prevent soil collapse near the ground surface and to allow flowback returns during drilling and cementing of other casings this casing can normally vary in nom |
inal size from 18 to 30 in 457 to 762 mm a casing of smaller diameter 13 in or 339 mm called a surface casing is placed inside the conductor casing and cemented in place to isolate freshwater aquifers that may be present near the surface an intermediate casing may be required for a deep well in which a well blowout induced by formation pore pressure or hydraulic fracturing caused by the drilling mud weight may occur the main functions of casings are for protective or preventive measures for production and or injection inner tubing with a liner typically 7 in or 178 mm in nominal size is used tubing is generally easier for replacement and maintenance completed wells can vary from vertical to deviated horizontal deviated horizontal wells have become more popular because of their greater accessibility and less impact on surface disturbance the performance of a completed well is a complex process involving the thermal hydraulic mechanical chemical interaction between the casing cement annulus and surrounding formations all subjected to different environmental loading the structural and hydraulic integrity of a casing well is governed by this coupled interaction in an ideal situation all drilling mud should be removed and the annular space should be filled with a cement slurry imperfect oil well cementing can produce weak and inhomogeneous cementitious material in the cement annulus if the complete displacement of drilling mud by the spacer fluid and cement slurry is not achieved a residual mud layer adhering to the inside and outside surfaces of the borehole and casing may be left localized channel or fingering may occur in the narrow spaces since the fluid displacement takes place in a narrow concentric annular configuration bounded by the circumferential surfaces of the drilled well and the steel casing fluid used in hydraulic fracturing or fluid from production can escape through the cement annulus behind the casing if the cement placement is not done properly in thermal wells under cyclic thermal loading thermally induced cracking in the cement annulus formation and interfaces could potentially jeopardize the structural and hydraulic integrity of the well in a production well withdrawal of water conventional gas or oil from deep reservoirs can result in reservoir compaction and consequently subsidence in the formations overlying the reservoir the subsidence can impair the casing reservoirs can experience dilation or expansion when stimulation techniques such as hydraulic fracturing or steam injection are applied during energy recovery hydraulic fracturing involves injection of fluids under high pressure into reservoir formations located at depth to fracture the formation steam injection produces dilatation of the reservoir due to an increase in pore pressure and thermal expansion of the reservoir which can exert stress and deformation to the overburden the resulting deformations induced during the re |
covery process could be excessive and detrimental to surface and subsurface facilities morgenstern et al 1988 casing failures have been reported in thermal recovery processes talebi et al 1998 mechanical energy released from hydraulically induced fractures or casing impairment and failure can generate microseismic events passive seismic monitoring using 3 component geophones along with geomechanical modeling have been employed in the field to determine the locations and mechanism of casing and formation failure piles are vertical or inclined structural members made of steel concrete or timber installed in the ground to transfer vertical and or horizontal load from a superstructure to founding ground tomlinson and woodward 2014 piles can be categorized according to their installation method precast concrete steel section or timber piles are driven into the ground by displacing in situ soil the driving process causes displacement and disturbance of the soil surrounding the pile another type of installation does not involve soil displacement the soil is removed by drilling or boring to form a shaft with a casing fig 2 in the excavation stage the casing prevents soil collapse or caving into the bored shaft concrete is then cast in the shaft with the casing being left behind or removed to form the pile steel casing is required in either type of installation steel circular piles made of hollow sections typically 30 60 cm in diameter are commonly used as nondisplacement piles such piles are easy for driving handling and fabrication and can be installed both onshore and offshore each pile must meet two criteria load capacity and settlement both the load capacity and settlement of a pile are determined by the soil pile interaction along the pile embedment length and at the pile bearing end the design method depends on the ground in which the pile is installed whether the soil is cohesive clay granular sand or competent bedrock piles founded in clay have different behavior in the short and long term because the pore pressure induced during pile placement and loading requires additional time for dissipation due to the low permeability of clay piles embedded in frozen soils in cold regions can creep for years and thus long term pile settlement is the critical design criterion for a complete design of a pile foundation system one is required to design a pile cap a pile cap is a structural member transmitting the loads from columns or walls of superstructure to the piles these are commonly built of reinforced concrete or steel sections piles are installed at a certain minimum spacing to maximize their carrying load capacity otherwise a reduction factor is required for design of a pile group in order to exercise quality control on pile performance pile load tests are carried out in the field two standard pile load tests are recommended in practice static and dynamic load tests in a static pile load test ax |
ial loads are statically applied to the test pile in increments and the settlement of the pile is recorded the axial loads can be applied by stacking concrete blocks on a loading frame attached to the pile or by exerting reaction forces using hydraulic jacks with a reaction frame the axial load settlement record provides the pile load capacity as a function of settlement the settlement has to be within the allowable range in a dynamic load test a dynamic load of known energy a falling hammer or dynamite charge is applied to the test pile while recording acceleration and strain on the pile head the recorded data can be used to analyze the dynamic response of the soil pile interaction using a wave propagation equation in viscoelastic medium test results give information on resistance distribution shaft resistance and end bearing and help evaluate the shape and integrity of the pile element the pile bearing capacity results obtained with dynamic load tests correlate well with those of static load tests performed on the same pile coastal defenses are measures taken to protect coastlines from erosion and other damage or to prevent flooding caused by the combined effect of sea waves extreme tides and storm surge they are designed to work by controlling wave action coastal currents and sediment movement on beaches each coastal defense method has its own advantages and disadvantages which should be carefully studied and weighed before adopting one into a given site construction in water is a difficult and dangerous job that requires a dry working surface cofferdams are one type of temporary structure designed to keep water and or soil from the execution of construction at a site so that the permanent facility structure can be constructed in water anderson 2001 a cofferdam should have waterproof walls more than 1 m higher than the maximum water level to ensure that water does not enter the opposite side cofferdam design and construction involve the consideration of the structure local soil and water conditions often construction offshore and the possibility of severe weather during construction the hydrostatic force of the water and the dynamic force due to currents and waves must be considered in the design cohesive soils are fine grained low strength and easily deformable soils that have a tendency for particles to adhere the soil is classified as cohesive if the amount of fines silt and clay sized material exceeds 50 by weight mitchell and soga 2005 examples of cohesive soils include sandy clay silty clay clayey silt and organic clay cohesive soils have significant cohesive strength and exhibit plasticity cohesion between soil particles comes from three major sources cementation electrostatic and electromagnetic attraction and primary valence bonding and adhesion mitchell and soga 2005 the structure of clay in cohesive soil has a great influence in the engineering behavior of soils the structure of |
soil refers to the geometric arrangement of soil or mineral particles and depends on genetic chemical mineralogical characteristic as well as past stress conditions of the soil interparticle force also influences the soil structure for cohesive soils interparticle force is much higher than in noncohesive soils most natural clay has highly oriented and dispersed structure due to tectonic activity by sliding or by construction activities such as compaction terzaghi et al 1996 most commonly used characteristics for cohesive soils are boundaries of fine stratification grain size distribution consistency limits maximum and minimum density specific gravity organic matter moisture content dry density porosity permeability void ratio compression index and shear strength the quality of cohesive soil samples is critical for the best geotechnical information and for planning the safe and economic design of structures some disturbance sources such as in situ stress mechanical disturbance and rebound are difficult to avoid when obtaining an undisturbed sample erodibility of cohesive soils is attributed to in situ condition and properties related to soil history soils that have the potential to collapse generally possess porous textures with high void ratios and relatively low densities at their natural moisture content these soils possess high apparent strength but they are susceptible to large reductions in void ratio on wetting especially under load in other words the metastable texture collapses as the bonds between the grains break down as the soil becomes saturated collapse of soils is controlled both microscopically and macroscopically and both aspects need to be understood if the controls on collapse are to be determined when collapse takes place there is a rearrangement of soil particles resulting in densification collapse typically takes place rapidly as the soil passes from a metastable condition to a normally consolidated one cut and cover is a tunnel construction technique preferred at a shallow depth in which excavation can be economically performed from the surface and the trench is subsequently covered with backfill after installation of all components for tunnel structures cut and fill works are often carried out in road railway canal housing constructions and mining etc fig 1 natural sites are usually undulating not level and must be modified before any construction can begin thus the cut and fill process is if necessary one of the first construction processes to take place on each development site an engineered barrier to the gravitational flow of water or other fluid that results in a reservoir for use in irrigation power generation water supply or flood control dams are constructed using soil rockfill concrete metal or blocks dams classified by use include storage dams are intended to impound water for specific uses such as water supply recreation wildlife or hydro |
electric power generation diversion dams are constructed to provide head for water conveyance systems canals ditches tunnels detention dams retard flood runoff to reduce the effect of sudden floods the process in which wet soils dry and soil moisture content decreases as the moisture evaporates into the surrounding environment leading ultimately to cracking of the ground surface during desiccation the bulk water pressure within the soil pores will become negative with respect to the atmospheric pressure this depression of pressure i e the difference between atmospheric pressure and bulk water pressure is known as the soil matric suction and is associated with the formation of curved water menisci within soil pores soil can shrink during desiccation the degree to which depends mostly on soil minerology and particle size for instance clay soils shrink more than sand due to desiccation soil shrinkage occurs in response to soil suction pulling soil particles closer desiccation cracking occurs when the desiccating soil is restrained against free shrinkage kodikara and costa 2012 the restraints could come from the friction at the boundaries such as at the base of a container or internally when some part of the soil dries faster than the other in nonuniform drying when the soil is restrained against free shrinkage tensile stresses can develop within soil initiation of shrinkage cracking happens when the tensile stress developed within restrained soil exceeds the soil tensile strength a site investigation is a planned field and office exercise used to obtain new information or verify existing data to support the design of a built structure excavation or site improvement it may include collecting surface and or subsurface information and be located on land underwater or a combination of both stress that causes a change in volume of a rock or soil reference cube without also causing a change in shape is called hydrostatic pressure because it acts equally in all directions thus hydrostatic pressure is a normal stress stress produced by tectonic forces external loads and excavations that may remove earth materials which provide support for adjacent earth material differs from the hydrostatic stress and can cause deformations and changes in shape the reference cube under purely hydrostatic stress conditions need not be rotated to an orientation in which the shear stresses reduce in magnitude to zero and the normal stresses become principal stresses because the hydrostatic pressure tensor consists of only normal stresses thus the hydrostatic pressure p can be subtracted from the normal stresses in the stress tensor resulting in the deviatoric stress tensor s dewatering is the process of lowering groundwater by pumping or installing cut off walls to prevent ingress of water into excavations or tunnels construction and mining projects often require excavations below groundwater level in soils and rocks where gr |
oundwater is encountered during excavation problems can occur either by flooding of the excavation or in the form of instability induced by its presence depending on the nature of the ground being excavated the groundwater conditions encountered can vary greatly from site to site a thorough hydrogeological investigation may be needed to allow groundwater conditions to be defined excavations below groundwater level often encounter problems including flooding and instability caused by groundwater inflows and pressures dewatering is used to allow excavations for construction mining and engineering purposes to be formed in workably dry and stable conditions there are two principal approaches to dewatering dewatering by pumping where an array of wells or sumps is pumped to lower groundwater levels and dewatering by groundwater exclusion which relies on low permeability cut off walls or ground treatment barriers to prevent or reduce groundwater inflows there are two principal objectives for dewatering the first is to prevent excavations below groundwater level from being inundated by groundwater the second and often more important objective is to avoid groundwater induced instability of the excavation by controlling pore water pressures and hence effective stresses around the excavation diagenesis is the sum of all chemical physical and biological changes that occur to sedimentary materials after deposition but before lithification conversion to sedimentary rocks diagenesis occurs at pressures and temperatures lower than those required for the formation of metamorphic rocks and can be broken down into early and late diagenesis although some workers restrict the term solely to early diagenesis dilatancy is the property of soil material that refers to a change in its volume in response to shearing under a certain normal or confining stress dispersivity is the tendency of some clayey or cohesive soils exposed to saturation by surface or groundwater to separate into individual particles instead of forming small clumps or aggregates of particles known as flocs dispersivity results in poor behavior of compacted soil embankments particularly those that impound water and can lead to failure caused by erosion associated with soil piping internal erosion into cracks fissures and joints or other macro scale openings or migration of soil fines into pore space between larger soil grains such as gravel or cobbles dissolution is the process by which soluble rocks such as limestone predominantly calcium carbonate chalk also calcium carbonate dolomite magnesium calcium carbonate gypsum hydrated calcium sulfate and halite rock salt sodium chloride are dissolved by the passage of water or weakly acidic water either over the rock surfaces or through fractures and pores in the rock dissolution of soluble rocks proceeds at varying rates depending on the mineralogy of the rock and composition of the water the rate is s |
lower in less soluble rocks limestone chalk and dolomite but quicker in more soluble gypsum over time the fractures become enlarged and increasingly interlinked eventually forming complex subsurface drainage systems and in the stronger rocks cavernous ground the dissolution features form a landscape known as karst which is typified by caves sinkholes dolines surface subsidence features caused by collapse into caves voids sinking streams surface streams that drain into sinkholes and springs emerging at lower levels engineering problems associated with soluble rocks include subsidence sinkhole formation uneven rock head and reduced rock mass strength sinkhole formation and subsidence has the potential to cause damage to buildings and infrastructure subsidence can be triggered by human disturbance of the ground a change in drainage patterns heavy rain or by water abstraction karstic rocks are often important aquifers so their vulnerability to pollution is of particular concern it is important to note that dissolution rates in limestone are so low that there is no threat to buildings or infrastructure from the creation of new cavities however cavernous gypsum can be enlarged much more quickly particularly beneath dams and reservoirs gypsum is also weaker than limestone and so collapses more readily salt near surface can be particularly hazardous to engineering the dissolution of gypsum and salt produce groundwater that is aggressive to concrete whereas salt is also very aggressive to steelwork drilling is an excavation process of rocks and soils in cylindrical form that requires special tools to provide direct access to geological geotechnical geochemical characteristics of corresponding geomaterials for different geological activities these geological activities can involve the exploration on type and distribution of mineral deposits extraction of rocks soils to provide detail on their physical mineralogical and mechanical properties for geotechnical projects efforts to reach oil shale gas and geothermal resources and other aims currently there are many different reasons to perform drilling in many engineering projects these are 1 opening a hole to describe in situ characteristics of soil and rock masses 2 extracting samples to measure physical mineralogical and mechanical properties of subsurface soils and rocks 3 performing in situ testing inside the drilling borehole to obtain strength and deformation properties of soil and rock mass and 4 reaching water mineral deposits and hydrocarbon resources to measure their geometries and spatial distributions or extraction drilling should be the final step after performing all preliminary assessment techniques such as site investigation geological mapping geophysical surveying opening trial pits and trenches and collecting disturbed and undisturbed samples from outcrops and carrying out required laboratory tests on these selected samples |
and thus obtaining an adequate database of information the location depth and number of drill holes are important controlling parameters of the project budget these parameters change depending on the importance and type of project geological conditions and information provided from preliminary studies below the comprehensive information related to drilling techniques sampling and borehole logging the in situ tests performed in boreholes borehole instability problems of drilling and finally developments recorded in deep drilling technology are discussed in detail no matter how much planning is done it is likely problems will arise while drilling a borehole the ability to maintain a stable wellbore is a challenge and becomes increasingly more difficult when completing directional sections within a small diameter hole and applying enough energy to clean out the borehole the most prevalent drilling hazards include geological faults and structures pipe sticking and drill pipe failures lost circulation borehole deviation pipe failures borehole instability formation contamination hydrogen sulfide or other gas hydraulic fracturing buried valleys and man made features in engineering geology abrasion is significant in three main ways erosion of the earth s surface damage caused by abrasive minerals and rocks to machinery selection of minerals that are suitable for use as industrial and domestic abrasives this is a complicated topic that is not yet fully resolved matters of specific interest include the relative ease or difficulty of resistance to excavation drilling or cutting of rocks and soils susceptibility to abrasion of surfaces including aggregates in highway pavements machinery and natural stone used in buildings to abrasion abrasion is often a two way process with the harder material affected less by wear than the softer material in general abrasion increases with hardness grain size and angularity of mineral content type of cementation degree of alteration and discontinuities in the rock forces of impacts and the overall mechanical properties of the soil or rock mass mineral particles carried by dynamic media cause abrasion of natural landforms and buildings and constructions the media are wind sediment carried by the wind sculpts distinctive landforms especially in arid areas but also during dry periods in less arid areas particularly where vegetation cover is absent sea water and lakes breaking waves carry sand and coarser particles against coastlines causing undercutting of slopes and cliffs and consequent landslides the resulting cliff retreat forms abrasion platforms adjacent to the shoreline and wave cut notches fig 1 similar processes occur in large lakes rivers rivers carry sand and coarser particles depending on the strength of the current that cause channel scour and erosion of river banks with consequent changes in geomorphology and b |
ank and slope stability ice debris frozen into the beds and lateral margins of glaciers and ice sheets erode and smooth adjacent rock surfaces these processes erode smooth and polish rock surfaces but also round and polish the debris that impact on those rocks plant machinery and other equipment are abraded during use causing wear and blunting and therefore contribute to significant costs of repair replacement and delays it is important to understand the potential for abrasion when costing engineering projects that involve drilling tunneling and mechanized excavation as well as grading cutting and shaping of mineral products such as aggregates and dimension stones majeed and abu bakar 2016 conversely abrasion is used in extraction of building stone by wire cutting techniques in which an armored wire and abrasives are used to cut and shape blocks a variety of minerals are used as abrasives selection of suitable pure or refinable materials depends on the minimum effective hardness these range from less demanding uses e g toothpastes and some domestic cleansers using calcite or feldspars to demanding industrial uses e g cutter heads or wires of strengthened metal and armored with very hard minerals a variety of abrasiveness tests have been developed for different purposes currently there is no universally accepted test for soil abrasiveness but much research is in progress mirmehrabi et al 2016 there is also an issue of the scale of tests these can be at a real scale in the tunnel excavation and borehole by examining resistance but this procedure is expensive and too late to do more than adjust the pattern of works it is more usual to undertake laboratory tests using scaled down equipment on samples which is more practical but less representative of the natural situation an alternative option is provided by geotechnical tests there have been two main approaches to testing abrasion abrasiveness the earliest focused on relative hardness of constituent minerals friedrich mohs defined a 10 stage hierarchy on the basis of which a mineral was strong enough to scratch another in that sequence talc softest gypsum calcite fluorite apatite orthoclase quartz topaz corundum and diamond hardest other minerals are then placed in this sequence between pairs of the listed minerals based on their ability to scratch or be scratched mohs scale is a relative scale it was later developed by rosiwal into absolute values measured in the laboratory taking corundum as having a value of 1000 an approach for use in the field is given in mol 2014 hardness may be determined in the field or laboratory by rebound devices such as the schmidt hammer most rocks and soils contain a variety of minerals which are variably affected by diagenetic and weathering processes that affect hardness therefore tests on individual minerals while useful are not wholly adequate for engineering geology purposes which re |
quires examination of mechanical properties of rock and soil masses mineral based texts also neglect the sizes and shapes of grains the cerchar abrasive test was developed to assess the potential abrasion damage to plant and equipment for instance cutter life in the field and is also significant for building and construction materials including dimension stone deliormanli 2011 it involves the use of an abrasive stylus to scratch a broken or cut surface of a sample strong correlation exists between the cerchar abrasivity index cai and rock strength and abrasion the rock abrasivity index was developed to take account of the content of abrasive minerals and the strength of the rock and is based on multiplying the unconfined compressive strength ucs and equivalent quartz content eqc of the sample plinninger 2010 the los angeles abrasion value test examines the resistance to degradation of bound aggregates in highway pavements a sample of coarse aggregate retained by a no 12 1 7 mm mesh sieve is weighed and is then subjected to abrasion and grinding in a steel drum the sample material is once again passed over a no 12 sieve and weighed the difference between the two weights is a measure of susceptibility to abrasion and therefore of the performance of the aggregate when subjected to abrasion during use abrasion is important in wind water and glacial erosion but it is also significant for determining the suitability of minerals for use as industrial and domestic abrasives blunting and wear on machinery such as that used in drilling and tunneling and the performance of aggregates during wear tests relate to the determination of hardness by scratching or by rebound on hammering or abrading samples to determine the rate of wearing down acid mine drainage is water encountered in and or draining from active or abandoned mines which has a low ph and or highly elevated concentrations of potentially ecotoxic metals mining disrupts the natural hydrogeological conditions in the subsurface often increasing the through flow of aerated waters resulting in oxidative dissolution of sulfide minerals the ferrous sulfide fes2 minerals pyrite and its less common polymorph marcasite release acidity when they dissolve this is not true of the non ferrous sulfide minerals this acidity can attack other minerals releasing further metals to solution clay minerals commonly dissolve to release al3 with mn2 zn2 and less commonly ni2 cu2 cd2 pb2 and the metalloid as also being mobilized where mineralogical sources for these are present above the water line dissolution is often incomplete and the products of sulfide oxidation accumulate as efflorescent hydroxysulfate minerals later dissolution of these will release acidity the resultant water is acid mine drainage albeit acidic is more correct in addition to low ph and elevated concentrations of iron and possibly other metals acid mine drainage is inva |
riably rich in sulfate the total acidity in mine drainage has two components proton acidity due to the presence of high concentrations of hydrogen ions h that manifest in a low ph below 6 would typically be regarded as acidic in this context and metal acidity due to the presence of the metals listed above that tend to react with any available alkalinity to form hydroxide minerals releasing further protons in the process in many mine waters the total acidity is exceeded by the total alkalinity which in the relevant ph range is predominantly accounted for by dissolved bicarbonate hco3 such mine waters are termed net alkaline where the total acidity exceeds the total alkalinity the mine water is termed net acidic this distinction is important many net acidic mine waters actually have a near neutral ph 6 where they first flow out at surface but after prolonged oxidation and hydrolysis of their metal acidity ph drops to strongly acidic levels 4 5 misidentification of net acidic waters as net alkaline on the basis of ph alone can be a costly mistake the principal concern with acid mine drainage is ecological as it often devastates aquatic life in receiving watercourses in engineering terms the high acidity poses heightened risks of corrosion of steel and other materials thus demanding careful galvanic protection the high sulfate concentrations pose a risk of rapid weathering of concretes based on ordinary portland cement sulfate resistant cements must be specified for structures likely to contact acid mine drainage acidic attack can weaken many rocks and engineering soils passive and active treatment methods are routinely used to treat acid mine drainage acidity ph is numerically equal to the negative decimal logarithm of the activity of ah or the concentration h of hydrogen ions in gram ions per liter this concept was introduced in 1909 by the danish chemist s rensen ph reflects the first letters of latin words potentia hydrogeni the power of hydrogen or pondus hydrogenii weight of hydrogen for low mineralized water the difference between activity and concentration of hydrogen ions is not geochemically significant but for high mineralized water the identification of activity and concentration is essential the introduction of ph as an indicator of acid base properties of aqueous solutions was founded on the ability of water to dissociate into ions according to the scheme h2o h oh in connection with this reaction and using the concept of ionic product of water kw ah aoh where kw ionic product of water ah and aoh activities of h and oh respectively kw at 22 c is equal 10 14 if the water does not contain other ions the h and oh concentrations are equal according to the electroneutrality of ion activities and at 22 c it has the value of 10 7 in that condition ph poh 7 the neutral reaction medium if h oh the solution is acidic ph 7 if h |
oh the solution is alkaline ph 7 the ph value is an important characteristic of all aqueous solutions and natural water bodies rivers lakes seas oceans the ph value along with the reduction oxidation redox potential determines the possible concentration in aqueous solutions of different chemical elements their migration forms and possible processes of changes of concentrations and properties of compounds it also has effects on soils and ecosystems both terrestrial and aquatic aeolian processes are processes related to wind in the atmosphere for engineering geology those processes which interact with the geosphere wind erodes transports and deposits materials especially in arid or semiarid areas with sparse vegetation cover and little soil moisture particularly where the substrate consists of unconsolidated sediments turbulent wind removes loose fine grained particles and entrains them as dust deflation or wears down surfaces by inter particle grinding and blasting or onto rock surfaces abrasion thereby creating more transportable material areas of long term sediment deflation result in a rock surface desert pavement deflation can form basin shaped depressions from centimetres to kilometres blowouts in size particles are transported in three different ways upwelling currents of air support small suspended particles less than 2 mm in diameter and can hold them in suspension indefinitely as haze or dust depending on how much is entrained sand sized particles can bounce some 1 cm above the ground surface at about half to one third of the wind speed saltation saltating particles can impact other grains that also saltate larger grains too heavy to saltate may be pushed rolled or slide creeping along surfaces aeolian turbidity currents arise when rain passes into arid areas causing cooler denser air to sink towards the ground when this reaches the ground it is deflected forward as wind and suspends mainly silt sized debris as dust storms suspension persists until the wind energy decreases and cannot support the weight of particles which are then deposited deposition is local if the particles are entrained near the ground and wind energy is low but dust can be transported for long distances in strong winds before deposition takes place if upwelling is strong enough to carry particles high into the atmosphere these can be distributed on the continental or global scale dust may be deposited sparsely into local soils but where frequent winds carrying large amounts of dust meet a barrier such as a mountain range thick silt deposits loess accumulate these are highly porous and have problematic engineering properties including compaction and collapse when moistened or affected by earthquakes wind across a loose dry surface moves and deposits particles locally wind over a sand grade surface may cause saltation forming troughs and crests with long axes perpendicular to the wind |
direction at distances wavelengths reflecting the average length of particle bounces the resulting ripples have the coarser material at the crests and finer material in the troughs larger scale movements build dunes by saltation and creep grains move up a slope towards a crest accumulate there and when the critical angle of repose is exceeded fall down the far side this angle is the steepest angle of dip to the horizontal plane to which a material can accrete without failing this causes a profile with a shallow back slope often covered with smaller ripples and a steep fore slope slip face nishimori and ouchi 1993 this repeated process causes slow advance of the dune until it is stabilized by changing climate and or armouring natural vegetation engineered surfaces dunes may sometimes grow to a few 100 m in height the characteristics of depositional structures are environmental indicators in the geological record wind has similar effects at a smaller and more local scale on dry uncohesive soils exposed by human activity such as sites stripped for quarrying construction and engineering works mine and quarry tips and tailings lagoons and ground cleared for agriculture leading to soil loss and deterioration dust emissions can be reduced by keeping exposed surfaces moist or stabilizing them and enclosing plant and equipment aeolian processes can be relevant to engineering geology and engineering geologists in several ways the difficult site investigation and sampling conditions where dry poorly consolidated sand or silt deposits occur at the ground surface the need for careful support of excavations and trenches and design of appropriate foundations in poorly consolidated aeolian deposits the potential for collapse of loess when affected by earthquakes or excessive moisture the avoidance of dust emissions from construction mining and quarrying sites the analysis for potentially hazardous minerals and elements in dust the protection of developments from incursions of aeolian deposits aerial photography is an image of the ground produced on light sensitive media including digital sensors or a film of light sensitive emulsion that has been taken from an elevated position unsupported by a ground based structure aerial photographs may be vertical 3 from the camera to the focal point of the image or oblique vertical air photographs are those taken looking straight down they are typically used for mapping and photointerpretation oblique refers to photographs taken at an angle to the earth surface orthorectified orthophotos vertical air photographs taken looking straight down apparently from an infinite distance and where perspective and terrain corrections have been geometrically rectified such that the image may be viewed as a map film types film types most commonly used in aerial photography are black and white color and near infrared black and white images were common in the 1970s but |
largely overtaken by color images near infrared aerial photography is taken where the film or sensor is sensitive to the near infrared spectrum 700 900 nm it is frequently used to identify vegetative health and to reduce the effects of haze infrared photography is often called false color photography the ability to view the earth from a distance to observe landforms patterns sources of change the propagation of processes through a geomorphological system for example and evidence for geological history are largely attributable to the invention development of and improvements to aerial photography air photographs provided foundational knowledge upon which modern engineering geology is based they contributed to many aspects of the field from basic cartographic mapping to the slow unveiling of geological solutions that changed our perception of fundamental principles such as the scablands example provided below topography engineering geology relies substantially on understanding the topographic ground surface before aerial photography important ground features were sketched or surveyed post wwii however the widespread use of stereo air photographs allowed for the creation of nationwide accurate topographic maps using a stereoplotter a mapper would float a red dot along the surface of the ground as viewed through two air photographs the red dot could then be moved along x and y axes following the ground contour while remaining at the same elevation tracing this dot led to the creation of contour lines and ultimately topographic maps all of north america was mapped in this fashion the usa having complete topographic coverage at 1 24 000 and canada at 1 50 000 today topography can be created from overlapping images both oblique and vertical using the same principles partially or fully automated by computers the forefront of this technology allows the user to take multiple overlapping images from a regular camera or even a phone and create a three dimensional model of the image see structure from motion below direct mapping geological data that impacts engineering design is routinely derived from air photographs structural features such as joints faults folds bedding planes and other lineaments are often discernable from detailed and even regional imagery constraint maps might include information about wetlands karst activity depth to bedrock and the various types of ground instability e g fig 3 and important resources such as aggregate are also readily found on air photographs direct mapping is used to support and extend the information found in borehole investigations for foundations or for linear infrastructure resources and land use change it would be hard to overestimate the contribution of aerial photography to the understanding and development of national resources in canada for example where population densities are low the historical record of timber resources agricultural la |
nd and changes in land use were accurately captured by repeated air photograph surveys much of the country is covered at intervals of 10 years or less beginning in the mid 1950s similarly changes in coastlines the widespread existence of permafrost the ongoing movements of rivers and the development of transportation corridors pipeline routes and transmission lines all benefited enormously from the air photograph record geomorphological and terrain maps historically relied on air photographs to guide and direct engineering efforts with respect to hazards unravelling the scablands finally air photographs give engineering geologists new insights into old problems the scablands are an excellent example in the 1920s geologists had firmly adopted the theory of uniformitarianism the notion that the surface of the earth s crust has developed because of uniform and continuous processes throughout geological history harlen bretz 1923 examined the massive rock cut channels and huge ripples in east central washington and proposed something different in what he named the channeled scablands bretz proposed a post glacial flood of such magnitude that it was not accepted by his colleagues not only did bretz s theories contradict uniformitarianism but others argued that no sufficient source of water was available in 1956 bretz published results from a second field trip this time including air photographs showing massive ripple beds tens of meters high that began to turn the tide of criticism that had marred his work to date although it would be another 20 years before his ideas were fully accepted air photographs were fundamental in the visualization of the processes and to find adequate sources of water to create the landforms an aeromagnetic survey ams is an airborne geophysical survey performed using a magnetometer aboard or towed behind an aircraft a magnetometer is an instrument used to measure the magnetic field aeromagnetic surveys are probably one of the most common types of airborne geophysical surveys the applications of ams in engineering geology include but are not limited to near surface geological mapping structural geology mapping aiding three dimensional 3d geological subsurface model construction groundwater study environmental study and geologic hazards assessment in an aeromagnetic survey an airplane flying at a low altitude carrying a magnetic sensor flies back and forth in a grid like pattern over an area recording disturbances in the magnetic field fig 1 height and grid line spacing determine the resolution of the data geologic processes often bring together rocks with slightly different magnetic properties and these variations cause very small magnetic fields above the earth s surface the differences in the magnetic field are called anomalies rocks or soils containing iron and nickel can have strong magnetization and as a result can produce significant local magnetic fields th |
e magnetic minerals contain various combinations of induced and remanent magnetization at exploration depths the earth s primary magnetic field is perturbed by the presence of magnetic iron oxide magnetite the most strongly magnetic and the most common magnetic mineral iron titanium oxides titanomagnetite titanomaghemite and titanohematite and iron sulfides pyrrhotite and greigite reynolds et al 1990 the remanent magnetization in the earth s magnetic field occurred during the mineral formation process whereas the induced magnetization was created by the presence of the earth s magnetic field the magnitudes of both induced and remanent magnetizations depend on the quantity composition and size of the magnetic mineral grains the goal of the magnetic method is to map changes in the magnetization that are in turn related to the distribution of magnetic minerals hoover et al 1992 magnetic measurements are usually made from low flying airplanes flying along closely spaced parallel flight lines additional flight lines are flown in the perpendicular direction to assist in data processing these large volumes of measurements are processed into a digital aeromagnetic map assisted by computer programs the geophysicist builds a geologic interpretation from the digital aeromagnetic data incorporating geological mapping and other geophysical information gravity seismic reflection where available fig 2 interpretations often involve both map based information e g a fault map and three dimensional information e g a geologic cross section and 3d geological model the workflow of the aeromagnetic survey method includes the aeromagnetic survey design data acquisition data processing and interpretation there are many parameters to consider in a typical aeromagnetic survey design these parameters include the line spacing of flying flying heights the flight line direction with the intention of maximizing the magnetic signature and features of the survey aircraft flight line spacing is determined by the degree of detail required in the final mapping or the size of exploration target and the funding available for the survey the strength of a magnetic field decreases approximately as the inverse of the square of the distance from the magnetic source therefore to record small variations in the fields aircraft must fly close to the ground as the aircraft flies the magnetometer measures and records the total intensity of the magnetic field at the sensor aeromagnetic data can be presented as contour plots or thematic maps e g fig 3 intensity of the aeromagnetic anomalies is expressed in these plots or maps as contour lines or different colors the shape depth and properties of the rock bodies causing the aeromagnetic anomalies can be interpreted by a trained geophysicist the magnetic anomaly map also allows a visualization of the geological structure of the upper crust in the subsurface particularly t |
he spatial geometry of bodies of rock and the presence of faults and folds because different rock types differ in their content of magnetic minerals even if the bedrock is obscured by surficial materials such as sand soil or water aggregate is granular material such as sand gravel or crushed stone used for a variety of purposes but most commonly in relation to construction activities natural aggregates sand and gravel occur in various deposits reflecting different processes of erosion transportation abrasion and deposition often representative of local regional lithologies and all textural classes the most common aggregate rich environments are fluvial and glacial deposits but coastal marine desert and other environments can also be exploited in a fluvial environment fine grained aggregates are more common in meandering river and distal high energy streams conditions whereas coarser aggregates occur in proximal high energy or braided stream conditions glacial environments are by nature more variable in sand and gravel composition but somewhat more predictable when relying on facies analysis and sequence stratigraphy e g glaciofluvial deposits crushed stone aggregate is typically derived at a local scale when natural aggregate is unavailable and is largely dependent on the bedrock lithology of the region most crushed aggregate is produced for concrete and road construction purposes most igneous rocks like dolerite and sedimentary rocks such as limestone and dolomite are excellent sources for crushed aggregate metamorphic rocks especially those with high cleavage and schistosity are a poor source for aggregate langer 1993 depending on the final purpose and use raw aggregate is processed in a number of ways including washing removal of detrital items sorting screening sieving etc the rock type shape and texture of aggregate strongly influence the range of uses for the materials for concrete and bituminous needs key properties of aggregate include hardness strength chemical properties size gradation particle shape contaminant absence specific gravity and so on aggregate is primarily used in construction activities but include a number of uses such as concrete cement and blocks road asphalt construction fill road subgrade bricks pipes roof shingles railroad ballast glass abrasives filtration beds fertilizer lime metallurgic fluxstone and so on the properties of aggregate are critically restrictive for certain uses and are subject to a suite of tests and technical specifications before adoption in some cases slag and clinkers are used as aggregate substitutes langer 1993 natural aggregate is typically mined through open pit operations or by dredging in water related environments crushed stone aggregate mining is commonly achieved by open pit or bank quarrying aggregate tests are tests performed on granular material such as sand gravel or crushed stone to determine the |
ir composition characteristics properties and suitability for specific uses natural and crushed stone aggregate serves a wide list of needs and uses around the world most aggregate is for construction purposes and of this most is used in portland cement concrete and bituminous mixes specific uses require specific requirements and attributes for the materials in use cement aggregate needs are more rigid and less flexible than for instance bituminous needs to ensure the most appropriate aggregate is used for a specific need a suite of tests are available to assess the composition characteristics properties and suitability of the aggregate materials the most common tests include abrasion test determines the hardness properties of aggregate most commonly relies on the los angeles abrasion test to establish the percentage of wear resulting from the rubbing action of steel balls abrasive charge on the aggregate samples cast iron spherical balls 48 mm in diameter 400 g are placed in a drum with 5 10 kg of aggregate after 500 to 1000 revolutions 30 rpm the sample is sieved weighed and compared to the total sample weight to provide a los angeles abrasion index bitumen adhesion test a number of tests are available to determine the reliability of adhesion of a bitumen binder to aggregate when water is present adhesion and binder stripping problems tend to arise when the bitumen mixture is permeable to water or the aggregate is exposed to wet and cold crushing test provides an indication of aggregate resistance to crushing under an applied crushing load the test requires samples of the aggregate to be subjected to standard load crushing conditions multiple layers of presieved materials are tamped 25 times before a 40 ton load is applied at a rate of 4 tons per minute the crushed aggregate is then sieved weighed and compared to the original total weight to provide an aggregate crushing value impact test determines the resistance of aggregates to impact forces multiple layers of sieved samples are tamped 25 times before a 14 kg hammer is dropped for a total of 15 blows the resultant sample is sieved and the weight is compared to the original sample to generate an impact value shape test this test provides an indication of the extent of detrimental flaky and elongated materials in the aggregate samples a flakiness gauge is used to define the percentage of particles whose smallest dimension is less than 6 10ths the mean size by weight an elongation gauge is used to define the percentage of particles whose longest dimension is 1 8 times the mean dimension by weight soundness test establishes the resistance of aggregate materials to prolonged weathering action sorted aggregate samples are subjected to 5 cycles of wetting saturated solution of sodium sulfate or magnesium sulfate and drying 105 110 c the weight loss in the sample provides a proxy indication of the disintegration potential of t |
he materials specific gravity water absorption tests involve two measures of specific gravity apparent specific gravity and bulk specific gravity the former determines sg of aggregate minus voids and the latter sg of aggregate sample including the voids the water absorption test is simply the difference between the two measures of specific gravity extensive testing can involve any combination of the following assessments aggregate crushing value bulk density chloride sulfate content clay and fine silt color flakiness index los angeles value mean least dimension organic impurities particle density water absorption particle shape particle size distribution petrographic examination polished aggregate friction value resistance to stripping resistance to wear sieve analysis soundness unconfined compressive strength weak particles and wet dry strength variation alkali silica reaction is the reaction between alkali in cement and noncrystalline or porous silica in aggregate in the presence of moisture that may cause expansion and cracking of concrete alkali silica reaction asr is an acid base reaction between calcium hydroxide portlandite ca oh 2 and silicic acid h4sio4 the alkaline solution reacts with amorphous silica to produce a viscous alkali silicate gel as the reaction proceeds ca2 ions are dissolved into the pore water these react with the gel to form solid calcium silicate hydrate whereas the alkaline solution converts the remaining siliceous minerals into bulky alkali silicate gel the increase in volume causes expansion pressure cracking and spalling that weakens the concrete and sometimes causes failure asr can be reduced or prevented by limiting silicate content of the aggregate by avoiding crushed rock or natural gravels containing amorphous or porous silica limiting the alkali metal content of the cement or preventing alkalis from external sources coming into contact adding fine grained siliceous materials as the cement is setting to promote a controlled reaction neutralizing excessive alkalinity a wide variety of rocks show alkali silica reactivity depending on the nature of contained silica including acidic and intermediate volcanic rocks obsidian rhyolite dacite andesite porphyries and tuffs granites and grano diorites shale slate sandstone siltstone quartzite siliceous carbonate rocks graywackes argillites chert and flint phyllites and granitic and grano dioritic gneisses suspect forms of silica are amorphous glasses and opal porous tridymite and cristobalite and microcrystalline chalcedony it is therefore important to carry out petrographical examination of potential aggregates and to undertake tests for potential alkali silica reactivity chemical methods crushed samples are reacted with 1 n sodium hydroxide at 80 c after 24 h the amount of silica dissolved from the aggregate and reduction in alkalinity of the solution are measured and plotted agains |
t a reference curve to establish whether these fall within one of three ranges innocuous deleterious or potentially deleterious the test identifies highly reactive aggregates fairly well but not slowly reactive aggregates and is helpful rather than reliable bar methods mortar bars are immersed in naoh solutions for 14 days or longer and changes in length are measured this is useful for aggregates that react slowly or expand late in the reaction however test conditions do not correspond to those of concrete in service and tend to overestimate aggregate reactivity the test indicates aggregates that are acceptable but not necessarily those that should be rejected alteration is any mineralogic change to a preexisting rock through chemical reaction caused by hot circulating hydrothermal fluids hydrothermal fluids owing to temperature and pressure gradient travel within a rock s primary or secondary porosity they react with country rock alter original mineralogy and produce new minerals hydrothermal fluids can be magmatic meteoric marine or sedimentary connate in origin they carry mobile elements large ion lithophile elements li be b rd cs alkalies alkali earths and volatiles the fluids responsible for inducing alteration of minerals may eventually deposit ore minerals as a result of thermal and chemical changes therefore mapping alteration halos is key to discovering hydrothermal mineral deposits that may or may not outcrop on the surface alteration is common with porphyry skarn and orogenic magmatic vein hosted low temperature epithermal volcanic massive sulfide deposits alteration associated with magmatic and sedimentary hosted deposits does exist but is not very conspicuous common alteration reactions include hydrolysis a reaction between silicate minerals and either pure water or aqueous solution hydration addition of water to produce a new mineral dehydration carbonitization addition of co2 to form carbonate rocks decarbonitization removal of co2 from minerals alkali alkali earth replacement addition of alkali or alkaline earth metals silication replacement or breakdown of silicate minerals by reaction with free silica silicification hydrothermal alteration in which quartz opal chalcedony jasper or other forms of the amorphous silica content of the rock increase and oxidation addition of oxygen reduction removal of oxygen depending on the chemistry of hydrothermal fluids and the wall rock various assemblages of alteration mineral products may result the most common assemblages include potassic e g k feldspar biotite propylitic e g chlorite epidote calcite phyllic e g sericite and argillic kaolinite montmorillonite minerals alteration indices are used to discriminate altered rocks from their unaltered counterparts and to quantify the degree of alteration the common alteration indices include the hashimoto ishikawa acnk silicification and c |
hlorite carbonate pyrite indices the angle of internal friction is a physical property of earth materials or the slope of a linear representation of the shear strength of earth materials earth materials that are unconsolidated and uncemented typically are called soil by engineers and geologists and may be called sediment by geologists soil consists of grains of minerals or rock fragments in a range of sizes mm to m from very fine to very coarse clay silt sand gravel cobble and boulder size grains that are chemically and mechanically separate from each other form a mass that can be excavated with relative ease and the excavated material can be placed in a pile that attains a conical shape with slopes that are at the angle of repose fig 1 the angle of repose is a representation of the angle of internal friction however it tends to be governed by grain shape such that the slopes of most piles of loose dry grains of natural soil are in the range of 28 to 34 a pile of angular gravel size grains can attain stable slope angles up to 45 shear strength of most soil is a function of the confining stress or normal stress nr such that it is lower at low normal stress and higher at high normal stress samples of alluvial silty medium to coarse sand subjected to direct shear testing might have a linear regression peak shear strength represented by eq 1 eq 1 describes an angle of internal friction of 33 5 and a cohesion intercept of 37 15 kpa a silty medium to coarse sand with nonplastic silt would be cohesionless a two parameter power function regression eq 2 of the same direct shear test data shows a variable angle of internal friction and forces the cohesion intercept to zero fig 2 which is appropriate for sandy soil the friction angle for the power function regression equation matches the linear regression at a normal stress value of approximately 118 kpa however the cohesion intercept for the tangent to the power function regression at this normal stress is 44 11 kpa earth materials are known to exhibit nonlinear strength and deformation behavior this example demonstrates the nonlinear strength aspect the shape of the coarse sand grains creates an equivalent roughness in the sample and is responsible for much of the nonlinear character in its shear strength the angle of internal friction is determined in a laboratory environment using a direct shear test or triaxial compression test theoretically the maximum angle at which grains in a heap of sediment can remain in place without becoming unstable the angle of repose of granular materials is relevant in various applications of science and engineering such as sedimentology geomorphology hydraulic and chemical engineering it can be used in the descriptions of initial motion of sediment grains and sediment transport process and in the investigations of bank stability riprap protection and reservoir sediment removal the angle of repose is |
measured using different methodstwo different slopes can be differentiated during the pile formation as grains are gradually added to a heap they can pile up to an upper angle of repose once masses slump a new surface will form at a lower angle of repose as a result the angle of repose varies repeatedly during the growth of the pile the upper angle is associated with the onset of slope instability and the lower angle is associated with the cessation of slope instability the upper angle of repose may also be measured as a critical angle using a tilting box for which some grains start to roll down along the inclined surface fig 2 in comparison the lower angle of repose is achieved at the end of an avalanche which can be generated by the removal of support for loose material fig 3 the angle of repose can also be measured by draining grains through a bottom opening of a container by building up a cone over a fixed base a rotating drum can be used to measure three different angles of repose fig 4 when the drum rotates a series of variations can be observed in the slope of the free surface of grains at a very low rotating speed grains move together with the drum demonstrating a rigid body motion until the slope reaches its upper angle then an increase in the slope angle triggers an avalanche transporting grains down the slope at the end of the avalanche a new slope forms at a lower angle if the rotating speed is increased both upper and lower angles disappear and the slope angle approaches a constant as grains keep rolling down the slope this indicates the beginning of the rolling stage the corresponding slope angle is referred to as the dynamic angle of repose at this stage grains move continuously from the upper to lower end of the slope yielding a surface shear layer of grains that flow down the plane inclined at a fixed angle theoretically the angle of repose can be considered the maximum angle at which grains can remain in place without becoming unstable unfortunately confusions often exist in the differentiation among the different angles of repose and thus the use of the term of angle of repose in the literature for example simons and senturk 1992 stated that the angle of repose is the angle of slope formed by particulate material under the critical equilibrium condition of incipient sliding soulsby 1997 applied the term of the angle of final repose for the angle of the lee slopes of dunes and the angle of slope of the conical scour around a circular vertical pile which is observed at the end of avalanching garcia 2008 considered the angle of repose as a slope angle beyond which spontaneous failure of the slope occurs an early differentiation between the upper and lower angles of slope was made by bagnold 1966 who called the upper angle the apparent limiting static friction angle of initial yield and the lower angle the residual angle allen 1969 described the upper angle as the ang |
le of initial yield and the lower angle as the residual angle after shearing carrigy 1970 noted that there is no agreement reached as to what angle should be measured francis 1986 indicated that some confusion exists in the precise meaning of the term angle of repose and a single angle of repose is inadequate to explain all observable characteristics of many scree slopes aquifer is a layer or a layered sequence of rock or sediment comprising one or more geological formations that can store and transmit significant quantities of water under an ordinary hydraulic gradient aquifer also includes the unsaturated part of the permeable material that is the part above the water table as well as the saturated part the sole saturated part of an aquifer or the part from the aquifer bottom to the water table is referred to as the effective aquifer the most important characteristics of aquifers are the storing capacity or capability to store water in the rock voids pores and fractures and the hydraulic conductivity which is the capability of water to move through the solid matrix the hydraulic conductivity derives from the interconnected pores of unconsolidated sediments sand and gravel or by the fracture network of consolidated sedimentary sandstone limestone igneous and metamorphic rocks some materials such as clay can have a high porosity but the scarce interconnection between pores makes such clay rich rocks quite impermeable thus creating a confining layer regarding the confining layer those layers with lower hydraulic conductivity aquifers can be classified as either unconfined or confined unconfined aquifer also known as phreatic aquifer or water table aquifer is one where the water table occurs within the aquifer layer in this type of aquifer the upper limit of saturation the water table is at atmospheric pressure and at any depth below the water table the pressure is greater than the atmospheric pressure and at any point above the water table capillary zone the pressure is less than atmospheric pressure the hydraulic heads measured in wells in an unconfined aquifer define a potentiometric surface that coincides with the water table the upper limit of saturation in plan view the water table surface is a contour map showing a horizontal distribution of heads in the aquifer groundwater pathways are perpendicular to the contour lines in a confined aquifer the entire thickness of the aquifer layer is saturated and there is a confining layer at the top of the aquifer at any point in confined aquifers the water pressure is greater than atmospheric pressure consequently the water level in a monitoring well in a confined aquifer rises above the top of the aquifer fig 2 the hydraulic heads measured in wells in a confined aquifer define the potentiometric surface an imaginary surface that does not coincide with the physical top of the aquifer in some heterogeneous settings lenses layers of le |
End of preview. Expand
in Dataset Viewer.
- Downloads last month
- 34