Geology Applied to Civil Engineering 土木工程地质 英文课件 第三章 Stratum and geological structures

3StratumandgeologicalstructuresGeologyAppliedtoCivilEngineering123contentsStratumRockformationCrustalmovement4Fold5Fracture5Geologicalmap1CrustalmovementBasically,bothtwocrustsformlithosphere,and"float"onthemantle.Becauseofconvectionintheunderlyingplastic(althoughnon-molten)uppermantleandasthenosphere,thelithosphereisbrokenintotectonicplatesthatarealwaysmoving.Themovementoftectonicplates,alsocalledcrustalmovement,generallyshowstwotypes:horizontalmovementandverticalmovement.Horizontalmovementmeansthemovementisgoingalongthetangential(orsimplyashorizontal)directionofearthsurface.Itcanbeshownbysubductionthatiscausedbyhorizontalsqueezingofearthcrusts.Itleadstofoldsandfracturesofrockformations,andformshugefoldmountainsandriftvalleys,aswellascontinentaldrift.Verticalmovementmeansthemovementisgoingalongthenormal(orsimplyasvertical)directionofearthsurface.Itcanbeshownbyverticalrisingorfallingofearthcrust.Itresultsinextensiveupliftingordepressionofearthcrust,thatisthereasonoftransgressionandregressionofthemarinesystem.2StratumIngeology,astratumisalayerofsedimentaryrocksorsoilswithinternallyconsistentcharacteristicsthatdistinguishitfromotherlayers.The"stratum"isthefundamentalunitinastratigraphiccolumn.Itisthebasisofthestudyonstratigraphy,sincethatagedatingofthestratumisthemajorsubjectinstratigraphy.Therearegenerallytwotypesofagedatingmethodsforthestratum,absolutedatingmethodsandrelativedatingmethods.2.1TheabsolutedatingmethodTheabsolutedatingmethodisamethodtodeterminetheabsoluteage(exactage)ofrocksinthestratumandothergeologicalitems,suchasmineralsandfossils.Absolutedatingmethods,byusingabsolutereferentcriteria(instratum),mainlyincluderadioactivedatingmethods,suchaspotassium-argondating,argon-argondating,uranium-leaddating,samarium-neodymiumdating,etc.Elementsmayexistindifferentisotopes,witheachisotopeofanelementdifferinginthenumberofneutronsinthenucleus.2.2Relativedatingmethods(1)LawofsuperpositionThelawofsuperpositionisanaxiomthatformsoneofthebasesofgeosciences,archaeology,andotherfieldsdealingwithgeologicalstratigraphy.Itisbasedontheassumptionthatthesedimentaryrockscanclearlyshowthesuperpositionrelationshipsofstrata.Thelawreferstothatinun-deformedstratigraphicsequences,theoldeststratawillbeatthebottomofthesequence,callednormalstratigraphySketchdiagramsshow:(a)normalstratigraphy;(b)reversestratigraphy.2.2Relativedatingmethods(2)BiostratigraphyBiostratigraphyisthebranchofstratigraphywhichfocusesontherelativeagesofrockstratabyusingthefossilassemblages.Theprincipleisthattheorganictextureandspeciescomplexofthefossilcouldindicatetheageofitssedimentaryrocks.Forexample,simpleorganictextureandspeciesoffossilindicatesthattheageoffossilanditsrocksisrelativelyold.Therefore,relativedatingmethodsofbiostratigraphyisusingthecomparisonoffossilstodistinguishtheageofstrata.Astageisamajorsubdivisionofstrata,andeachsystematicallyfollowingtheothereachbearingauniqueassemblageoffossils,andthusthefossilusedtodefineandidentifygeologicperiodsiscalledtheindexfossil(alsoknownasguidefossils).2.2Relativedatingmethods(3)Stratigraphicrelationships1)ContactrelationshipsinsedimentaryrocksBasically,contactrelationshipsinsedimentaryrockscouldbedividedintotwotypes,conformityandunconformity.Sketchdiagramsshow:(a)conformity,(b)disconformityand(c)angularunconformity.2.2Relativedatingmethods2)ContactrelationshipsinmagmaticrocksContactrelationshipsinmagmaticrocksaremainlycross-cuttingrelationships.Itisarelativedatingtechniqueandaprincipleingeologythatstatesthegeologicfeaturecuttingintotheotheristheyoungerone.Intrusionrelationshipsoccurwhenanigneousplutonordikeintrudedintopre-existingcountryrocks.Alight-grayigneousintrusioninSwedencutbyayoungerwhitepegmatitedikewhichinturniscutbyanevenyoungerblackdiabasedike(modifiedfromCarlsonetal.,2011).2.2Relativedatingmethods3)Contactrelationshipsbetweensedimentaryrocksandmagmaticrocksa)IntrusivecontactIntrusivecontact,alsocalledthermalcontact,isacontactrelationshipoccurringwhenlatermagmaticrocksintrudeintosedimentaryrocks.Itcommonlyoccursaroundintrusiveigneousrocks,asaresultofthetemperatureincreasedbytheintrusionofmagmaintocoolercountryrocks(mostlyaresedimentaryrocks).b)SedimentarycontactSedimentarycontact,alsocalledcoldcontact,isacontactrelationshipoccurringwhenlatersedimentaryrockscoveronearliermagmaticrocks.Theearliermagmaticrocksoftenundergoweatheringanderosionduetoexposingontheearthsurface,thus,thebottomofthelatersedimentaryrocksarecommonlybasalconglomeratesincludingmagmaticgravelssourcedfromtheearliermagmaticrocks.2.3Geologictimescalethetableofgeologictime(dataisfromthelatestversion(v2021/10)oftheInternationalChronostratigraphicChartpublishedbyInternationalCommissiononStratigraphy).3RockformationCrustalmovements(orstructuralmovements)maycausedeformationandmovingofrockformations,andthosedeformationandmovingarereservedandcalledgeologicalstructures.Therearemainlyfivetypesofgeologicalstructures:horizontalrockformation,inclinedrockformation,verticalrockformation,foldsandfaults.Theattitudeofrockformationisthestateofspatialdistributionofrockformations.Basedontheattitudes,rockformationsaredividedinto:horizontalrockformation,showingasmallincludedangle(<5°)inclinedrockformation,showingincludedangles(from5°to85°)verticalrockformation,showingalargeincludedangle(>85°)AttitudeofrockformationThestrikereferstotheorientationofarockformation.Thedipdirectionisavectordirectionofthedipasprojectedtothehorizontal,whichisperpendiculartothestrikedirection(±90°).Thedipangleisthedescentangleofarockbedrelativetoahorizontalplane,andisgivenbythenumber(0°-90°).4FoldThefoldingstructureischaracterizedbythesymmetricalrepetitionofthestrata.Todeterminegeometricfeaturesofthefoldform,therearemanypartsofthefoldnamedasshowninFig.3-11.Thecenterpartofafoldisalsocalledthecore.Alimbofthefoldisthepartbesidethecore,andnormallytherearetwolimbsinafold.Theaxisplaneofafoldistheimaginaryplanewhichcanequallydividethefold.Thehingelineofafoldisintersectionlinesoftheaxisplaneandeachfoldingbed.Inaddition,theaxialtraceofafoldistheintersectionlineofaxisplaneandhorizontalplane.4.1BasictypesoffoldAnanticlineisafoldshapedlikeanarchwiththeoldestrocksinthecenterofthefold.Asynclineisafoldshapedlikeatroughwiththeyoungestrocksinthecenterofthefold4.2classificationbasingonattitudesofaxialplaneandlimbsAnuprightfoldhasaverticalaxialplaneandtwolimbswithsimilardipanglesandoppositedipdirections.Aninclinedfoldhasaninclinedaxialplaneandtwolimbswithdifferentdipanglesandoppositedipdirections.Anoverturnedfoldhasaninclinedaxialplaneandtwolimbswithsamedipdirections.Arecumbentfoldhasanalmosthorizontalaxialplane.uprightfoldinclinedfoldoverturnedfoldrecumbentfold

4.3classificationbasingonattitudeofthehingeAplungingfoldhasthehingelinenothorizontal.Onasurfaceofplungingfoldsleveledbyerosion,thepatternsofexposedstrata(beds)resembleV-shapedorhorseshoes.Thestructuraldomecanbeformedbytheplungingfoldswitherosion.Annon-plungingfoldhasahorizontalhingeline.Thestratigraphicboundariesonthegroundsurfaceareparalleltoeachother.PlungingfoldsStratumofnon-plungingfoldsStratumofplungingfolds5FractureIfrocksarebrittle,thefractureispossibletobeformedbymovementsordisplacementsofrocks.Ifnoobviousmovementordisplacementoccursinthefracture,therockisjointed.Ifoneithersideofafractureitmovesalongthefractureplane,therockisfaulted.Sincemostrocksatornearthesurfacearebrittle,nearlyallexposedbedrocksarejointedorfaultedtosomeextent.5.1JointJointsareoneofthemostcommonlyobservedstructuresinsedimentaryrocks,magmaticrocksandmetamorphicrocks.Ajointisafractureorcrackinarockbodyalongwhichessentiallynodisplacement.Photographsshowingjointsinrocks:(a)Verticaljointsinmudstones(b)Columnarjointsinmagmaticrock(Cenozoicbasalt)atNiutouMountain,Fujian,China.ClassificationofjointsJointsareclassifiedbasedonitsorigin,mechanicalpropertyandgeometry.Originaljoints(orprimaryjoints)andsecondaryjointsareclassifiedbasedontheorigin.Originaljointsarethefractureformedduringthediagenesis.Secondaryjointisthefractureafterthediagenesis,includingtectonicjointsandsupergenejoints.

Tectonicjointsareformedwhentherelativedisplacementofthejointwallsisnormaltoitsplaneastheresultofbrittledeformationofbedrockinresponsetoregionaldeformationofbedrock.

Supergenejointsareformedbyweathering,loading,exfoliationandotherssupergeneoriginsincludinghydraulicjoints,exfoliationjoints,unloadingjointsorreleasejoints,forexample.ClassificationofjointsShearjointsandtensionjointsareclassifiedbasedonthemechanicalpropertyofjoints.Shearjointsarejointsformedbytheshearstresswhichexceedstheshearstrengthoftherocks.Shearjointsarecharacterizedbyflatfractureswithslickenside,fillingssuchascalcite,cuttingintotheconglomerate,extendinginthelongerdistance,conjugatedasX-shapedjoint.Tensionjointsarejointsinrockscausedbythetensilestresswhichexceedsthetensilestrengthoftherocks.Tensionjointsarecharacterizedbyhacklyordendriticfractureswithoutslickenside,fillingssuchascalcite,cuttingbesidetheconglomerate,extendingintheshorterdistance,combinedasechelonjointsystem.ShearjointsTensionjointsClassificationofjointsBasedonthegeometryofjoints,suchasarelationshipbetweenattitudesofjointsandrocks,jointsareclassifiedinto4types:strikejoint,dipjoint,slopingjointandbeddingjoint.Astrikejointhasthesamestrikedirectionasthatofrockbeds.Adipjointhasthesamedipdirectionasthatofrockbeds.Aslopingjointisthejointwithadifferentdirectionofstrikeanddipfromthatofrockbeds.Abeddingjointisthejointroughlyparalleltorockbeds,showingthesameattitudes.

Adiagramshowingfourtypesofjointsclassifiedbytheirgeometry:1-strikejoint;2-dipjoint;3-slopingjoint;4-beddingjoint.InvestigationofjointsInvestigationcontentsofjointsmainlyincludeitsdevelopmentdegrees,origintypes,mechanicalproperties,attitudes,densities,openingdegreeandfillings.

Developmentdegreeofjointsisdecidedbythenumberofjointsystemsobservedintherockbody.

Origintypeandmechanicalpropertyofthejointarethebasisoftheclassification,theyarethusmajorjobsintheinvestigation.

Thedensityofjointsmeansthenumberofjointsintheunitareaortheunitvolume.

Theattitudeofjointscanbemeasuredbythecompass.

OpeningdegreeandFillingsofjointsarealsoanimportantcontentintheinvestigation,thatthemineral,thethicknessandwatercompositionarerequiredtobeclear.5.2FaultIngeology,afaultisaplanarfractureordiscontinuityinavolumeofrock,acrosswhichtherehasbeensignificantdisplacementasaresultofrock-massmovement.Thus,faultsarefracturesintherockalongwhichslidinghastakenplace.Photographsshowingjointsinrocks:(a)Verticaljointsinmudstones(b)Columnarjointsinmagmaticrock(Cenozoicbasalt)atNiutouMountain,Fujian,China.ClassificationoffaultsClassificationoffaultsisgenerallyaccordingto3relations:relativemovementdirectionofhangingwallandfootwall,therelationbetweenattitudeoffaultandrockbedsandtherelationbetweenstrikeoffaultandaxiallineoffold.Threetypesoffaultsillustratedbydisplacedblocks(modifiedfromCarlsonetal.,2011):(a)Dip-slipfaults(normalfaultandreversefault);(b)Strike-slipfault;(c)Oblique-slipfault.Althoughbothblocksprobablymovewhenthefaultslips,theheavierarrowsshowonlythedirectionofmovementontheleft.