Unit 8SoilMechanicsText Soilsareaggregatesofmineralparticles,andtogetherwithairand/orwaterinthevoidspaces,theyformthree-phasesystems.Alargeportionoftheearth’ssurfaceiscoveredbysoils,andtheyarewidelyusedasconstructionandfoundationmaterials.Soilmechanicsisthebranchofengineeringthatdealswiththeengineeringpropertiesofsoilsandtheirbehaviorunderstress. Theprimarymechanismofsoilcreationistheweatheringofrock.Allrocktypes(igneousrock,metamorphicrockandsedimentaryrock)maybebrokendownintosmallparticlestocreatesoil.Weatheringmechanismsarephysicalweathering,chemicalweathering,andbiologicalweathering.[1]Humanactivitiessuchasexcavation,blasting,andwastedisposal,mayalsocreatesoil.Overgeologictime,deeplyburiedsoilsmaybealteredbypressureandtemperaturetobecomemetamorphicorsedimentaryrock,andifmeltedandsolidifiedagain,theywouldcompletethegeologiccyclebybecomingigneousrock. Physicalweatheringincludestemperatureeffects,freezeandthawofwaterincracks,rain,wind,impactandothermechanisms.Chemicalweatheringincludesdissolutionofmattercomposingarockandprecipitationintheformofanothermineral.Clayminerals,forexamplecanbeformedbyweatheringoffeldspar,whichisthemostcommonmineralpresentinigneousrock.Text Anaturallyoccurringsoilsamplemayhaveparticlesofvarioussizes.Overtheyears,variousagencieshavetriedtodevelopthesizelimitsofgravel,sand,silt,andclay.SomeofthesesizelimitsareshowninTable8.1.ReferringtoTable8.1,itisimportanttonotethatsomeagenciesclassifyclayasparticlessmallerthan0.005mminsize,andothersclassifyitasparticlessmallerthan0.002mminsize.However,itneedstoberealizedthatparticlesdefinedasclayonthebasisoftheirsizearenotnecessarilyclayminerals.Clayparticlespossess,thetendencytodevelopplasticitywhenmixedwithwater;theseareclayminerals.Kaolinite,illite,montmorillonite,vermiculite,andchloriteareexamplesofsomeclayminerals[2].Table8.1Soil—separatesizelimitsTextTextText Animportantfunctioninthestudyofsoilmechanicsistopredictthestressesandstrainsimposedatagivenpointinasoilmassduetocertainloadingconditions.Thisisnecessarytoestimatesettlementandtoconductstabilityanalysisofearthandearth-retainingstructures,aswellastodeterminestressconditionsonundergroundandearth-retainingstructures. Estimationoftheincreaseinstressatvariouspointsandassociatedisplacementcausedinasoilmassduetoexternalloadingusingthetheoryofelasticityisanimportantcomponentinthesafedesignofthefoundationsofstructures[3].Theidealassumptionofthetheoryofelasticity,namelythatthemediumishomogeneous,elastic,andisotropic,isnotquitetrueformostnaturalsoilprofiles.Itdoes,however,provideacloseestimationforgeotechnicalengineersand,usingpropersafetyfactors,safedesignscanbedeveloped. Aknowledgeoftheincreaseofporewaterpressureinsoilsduetovariousloadingconditionswithoutdrainageisimportantinboththeoreticalandappliedsoilmechanics[4].Ifaloadisappliedveryslowlyonasoilsuchthatsufficienttimeisallowedforporewatertodrainout,therewillbepracticallynoincreaseofporewaterpressure.However,whenasoilissubjectedtorapidloadingandifthecoefficientofpermeabilityissmall(e.g.,asinthecaseofclay),therewillbeinsufficienttimefordrainageofporewater.Thiswillleadtoanincreaseoftheexcesshydrostaticpressure.Text Anygivenmassofsoilconsistsofsolidparticlesofvarioussizeswithinterconnectedvoidspaces[5].Thecontinuousvoidspacesinasoilpermitwatertoflowfromapointofhighenergytoapointoflowenergy.Permeabilityisdefinedasthepropertyofasoilthatallowstheseepageoffluidsthroughitsinterconnectedvoidspaces.Whenasoillayerissubjectedtoacompressivestress,suchasduringtheconstructionofastructure,itwillexhibitacertainamountofcompression.Thiscompressionisachievedthroughanumberofways,includingrearrangementofthesoilsolidsorextrusionoftheporeairand/orwater.AccordingtoTerzaghi(1943),“adecreaseofwatercontentofasaturatedsoilwithoutreplacementofthewaterbyairiscalledaprocessofconsolidation.”Whensaturatedclayeysoils—whichhavealowcoefficientofpermeability—aresubjectedtoacompressivestressduetoafoundationloading,theporewaterpressurewillimmediatelyincrease;however,becauseofthelowpermeabilityofthesoil,therewillbeatimelagbetweentheapplicationofloadandtheextrusionoftheporewaterand,thus,thesettlement.Thisphenomenoniscalledconsolidation. Theshearstrengthofsoilsisanimportantaspectinmanyfoundationengineeringproblemssuchasthebearingcapacityofshallowfoundationsandpiles,thestabilityoftheslopesofdamsandembankments,andlateralearthpressureonretainingwalls.NewWordsandPhrasessilicaten.硅酸鹽metamorphica.變形的；變質的；改變結構的sedimentarya.（巖石）沉積形成的dissolutionv.解散；溶解；融化precipitationn.（雨雪）降落；降雨量plasticityn.粘性；成形性，柔軟性strainn.拉緊，繃緊；拉力；張力；應變displacement代替；取代；移位；轉移；置換elasticitya.可伸縮的；靈活的，能適應的；有彈性的，有彈力的homogeneousa.同形態(tài)（固態(tài)、液態(tài)或氣態(tài)）的；同種的,同類的,相似的geotechnicala.土工技術的；地質的，土工的permeabilityn.透過性；滲透性，滲透率hydrostatica.靜水力學的，流體靜力學的seepage（液體或氣體的）滲出，滲漏extrusion擠出；推出；噴出consolidation鞏固；強化；使堅強；使結實retainingwallsn.擁壁；擋土墻；護岸geologictimen.地質時期igneousrockn.火成巖metamorphicrockn.變質巖sedimentaryrockn.沉積巖compressivestressn.壓應力Notes1.Weatheringmechanismsarephysicalweathering,chemicalweathering,andbiologicalweathering. 風化機理包括物理風化、化學風化和生物風化。2.Kaolinite,illite,montmorillonite,vermiculite,andchloriteareexamplesofsomeclayminerals. 高嶺土、伊利石、蒙脫石、蛭石和綠泥石是粘土礦物的一些示例。3.Estimationoftheincreaseinstressatvariouspointsandassociatedisplacementcausedinasoilmassduetoexternalloadingusingthetheoryofelasticityisanimportantcomponentinthesafedesignofthefoundationsofstructures. 使用彈性理論評估各個位點壓力的增加以及由外部負荷引起的土壤質量的附加位移是安全設計建筑物基礎的重要保障。4.Aknowledgeoftheincreaseofporewaterpressureinsoilsduetovariousloadingconditionswithoutdrainageisimportantinboththeoreticalandappliedsoilmechanics. 在不排水情況下，由各種負荷條件造成土壤中孔隙水壓力的增加是理論土力學和應用土力學的重要內容。5.Anygivenmassofsoilconsistsofsolidparticlesofvarioussizeswithinterconnectedvoidspaces. 任何給定的土壤質量均由各種尺寸的固體顆粒（包括緊密連接的空隙空間）所組成。Exercise（TranslatethefollowingChineseintoEnglish,orEnglishintoChinese）1.因為可以通過碾壓、夯實、搗振或其他方法壓實土以增加其密度和提高其承載強度，所以可壓縮性是土的一個重要特性。2.通過測定震動波傳到基巖和作為反射波回到地面所需的時間，可確定基巖的深度。3.Thegeneraltermweatheringembracesanumberofnaturalsurfaceprocesseswhichresultfromthesingleorcombinedactionsofsuchagenciesaswind,rain,frost,temperaturechangeandgravity.4.Allsoilsoriginate,directlyorindirectly,fromsolidrocksandtheseareclassifiedaccordingtotheirmodeofformationasfollows:IGNEOUSROCKSformedbycoolingfromhotmoltenmaterial(‘magma’)withinoronthesurfaceoftheearth’scrust,e.g.granite,basalt,dolerite,andesite,gabbro,syenite,porphyry.SEDIMETARYROCKSformedinlayersfromsedimentssettlinginbodiesofwater,suchasseasandlakes,e.g.limestone,sandstone,mudstone,shale,conglomerate.METAMORPHICROCKSformedbyalterationofexistingrocksdueto:(a)extremeheat,e.g.marble,quartzite,or(b)extremepressure,e.g.slate,schist.Exercise（TranslatethefollowingChineseintoEnglish,orEnglishintoChinese）5.Thecommonproblemareasinsoilmechanicsmaybeconvenientlysummarizedas:(1)Excavation.Thediggingandremovalofsoilinordertoprepareasiteforconstructionandservices.Theproblemsherearecloselyrelatedtothoseofsupport.(2)Supportofsoil.Inthecaseofbothnaturalandbuiltslopes(embankments),itisnecessarytodeterminetheirintrinsicabilityforself-support.Whereexcavations(e.g.trenches,basements,etc.)orothercuts(e.g.roadcuttings)aretobemade,itwillbenecessarytodeterminetheneedfor,andtheextentof,externalsupport.(3)Flowofwater.Theeffectsofwaterinsoilmassesmustbeconsideredthoroughly.Whereasoilispermeableandwatercanflowthroughit,problemsrelatedtothequantityandeffectsofseepagearise.(4)Soilasasupportmedium.Themassofsoilunderand