Geology Applied to Civil Engineering 土木工程地质 英文课件 第十一章 Geologic problems in slope engineering

110GeologicproblemsinslopeengineeringGeologyAppliedtoCivilEngineering123contentsFactorsinfluencingSlopeStabilitySlopeStabilityAnalysisFailurepatternofArtificialSlope4CountermeasureforPreventingSlopefailure231FailurepatternofArtificialSlopeTheclassificationofthebasictypesofslopedeformationandfailureisthebasisforthestudyofslopestabilityandslopestabilization.FailurepatternsofsoilcuttingslopeAccordingtothescaleoffailures,thephenomenonoffailuresinsoilcuttingcanbedividedintotwomaincategoriesa)BenchfacefailureThemaintypesofbenchfacefailureincludesurfaceerosionandsurfaceslumping.Erosionisthephenomenonofrainwaterrunoffontheslopecarryingawaylooseparticlesfromtheslopeduetodynamicaction,oftenformingstripedgulliesontheslopesurface.Slumpingismostlycausedbyexcavationdisturbance,rainwaterleachingandscouring.Patternsofbenchsurfacefailureonsoilcuttingslope;(a):Surfaceerosion;(b):Surfaceslump41FailurepatternofArtificialSlopeFailurepatternsofsoilcuttingslopeb)SlopebodyfailureItreferstotheoverallfailureoftheslope.Overallslopecollapseandlandslidearebothslopefailure.Continuoustensioncracksandsinkingatthetoporupperpartofasoilslope,orbulginginthemiddleorlowerpartofaslope,aresignsofoverallslopefailure.Ingeneral,thistypeoffailureoccursduringoraftertherainyseason.Inthecaseofweaksubstrates,theslopefailureisoftencombinedwiththefailuretothesubstrate.Forthistypeoffailure,forecastingshouldbestrengthenedduringthewarningperiodtopreventaccidentsfromoccurringunawares.Thecauseofthefailuremustbeidentifiedbeforetreatment,andtheexcavationmustnotbeclearedatwilltoavoidfurthercollapseandexpansionofthefailure.51FailurepatternofArtificialSlope(2)FailurepatternsofrockslopeRelaxationRiverundercuttingormanualexcavationcausesagradualreductionintheminimumprincipalstressintherockandsoilbodywithintheslope,andtherockbodyatthesuperficialpartoftheslopesurfaceevenchangesfromathree-waystresstoatwo-waystressstate.Duringthisprocess,aseriesofsteeplydippingtensionfissuresareoftencreatedintherockbody,whicharenearlyparalleltotheslopesurface,andaregraduallypulledapartandopened.Relaxationofunloadingduetooccurrenceofexcavationinajointedrockslopeoutcroppedsandwichbetweenlimestoneandsandstone61FailurepatternofArtificialSlope(2)Failurepatternsofrockslopeb)CreepCreepisthelong-termslowdeformationofarockmassundertheactionofgravity.Thistypeofdeformationmostlyoccursinsoftandweakrock(suchasshale,micaceousrock,schist,etc.)orsoftandhardinterbeddedrockbodies(suchassandshaleinterbedded,shaletuffinterbedded,etc.),oftenformingflexuraldeformation.Superficialcreep;Deepcreep.Bendingcreepdeformation71FailurepatternofArtificialSlope(2)Failurepatternsofrockslopec)SpallingSpallingisaphenomenoninwhichtherockofaslopeisafailurebylong-termweatheringandthesurfacerockisbrokendownintorockchipsandsmallpiecesofrockthatrolldowntheslope.Themainreasonforspallingisthedestructionoftherockstructureduetovariousphysicalweathering.d)SlipfailureSlipfailureisaphenomenoninwhichtherockonaslopemovesdownwardsalongacertainfaceorbelt,anditisoneofthecommonformsofdeformationfailuretorockyslopes.Thespecificformsoffailureinslopesaremostlydownwardslidinganddouble-sidedwedgesliding.e)CollapseandRockfallCollapseisthesuddendownwardfallofamassiverockmassonasteepslopeundertheinfluenceofgravity;whilearockfallisthedownwardfallofanindividualrockmass.82FactorsinfluencingSlopeStability(1)RockandsoilpropertyThestabilityofrockslopesismoreclearlyrelatedtothetypeofrockthatmakesuptheslope.Ingeneral,magmaticrocksarestrongerthansedimentaryrocks;paramorphicrocksmetamorphosedfromsedimentaryrocksarestrongerthantheoriginalrocks(e.g.quartziteisstrongerthanquartzsandstone),andtheslopestheyformcanbehigherandsteeper;slopesofasinglelithologyaremorestablethanthoseofcomplexlithology;fine-grainedrocksaremorestablethancoarse-grainedones;massiveonesaremorestablethanflakes;slopescontainingmorequartzandfeldspararemorestablethanthosecontainingmoremicaschist.Ifanalyzedfromlithologyalone,rockswithhighdensity,highstrengthandhighresistancetoweatheringcanformhighandsteepslopeswithbetterstability.92FactorsinfluencingSlopeStability(2)GeologicalstructureInareaswhereregionalgeologicalstructuresaremorecomplex,foldsarestronger,largefissurezonesaremoredevelopedandnewtectonicmovementsrelatedtoearthquakesaremoreactive,slopestabilityispoor.Inthevicinityofthefaultandthecoreofthefold,therocklayerisbrokenandthejointsaredeveloped,hence,thestabilityoftheslopeisalsopoor.102FactorsinfluencingSlopeStability(3)GeotechnicalcontextureSoilswithahighcontentofflakeminerals(e.g.expansivesoilscontainingmontmorilloniteandillite)areusuallymorelikelytoaffectthestabilityofslopes.Theinfluenceofrockstructureonslopestabilityissometimesdecisive.Thelaminatedandschistosesurfacespresentinsedimentaryandparamorphicrocksoftenbecomeslidingsurfacesforrockslopefailurewhenthetendencyoftherockissimilartotheslopesurfaceandthedipangleislessthantheslopeangle.Thecuttingcombinationofvariousdiscontinuoussurfacespresentintherockoftenconstitutesanunstableblockoftheslopeandaffectsthestabilityoftheslope.112FactorsinfluencingSlopeStability(4)GroundandSurfacewaterTheimpactofwateronslopestabilitycanbedividedintothreeaspects:firstly,thesofteninganderosionoftherockandsoilbywater,whichreducesthemechanicalpropertiesoftherockandsoil;secondly,theformationofhydrostaticandseepagepressure,whichchangestheforcestateoftheslope;thirdly,thescouringanderosionoftheslopebywater,whichdirectlyfailurestheslope.122FactorsinfluencingSlopeStability(5)WeatheringWeatheringreducesthestrengthoftherockandsoilmass,decreasesthestabilityoftheslopeandpromotesthedeformationandfailureoftheslope.Alargenumberofinvestigationshaveshownthatthemoreserioustheweatheringofthesloperock,theworsethestabilityoftheslope,andthesmallertheslopeangleforslopestability.Inthesamearea,thedegreeofweatheringisdifferentfordifferentlithologies.132FactorsinfluencingSlopeStability(6)EarthquakeTheimpactofearthquakesonslopestabilityismanifestedintwoways:changingthestressstateofthesloperock,increasingtheseismicforceinthedirectionoutsidetheslopeonthebasisoftheoriginalstressstate;causingtherocktopullapartorcausingtheoriginalclosedfissurestoopen,formingunstableblocksontheslopeandenhancingtheactionofsurfacewaterandgroundwater.(7)HumanactivitiesInadequatehumanexcavationofslopes,failuretovegetationandanthropogenicalterationofsurfaceorsubsurfacehydrodynamicconditionsallcancauseslopefailure.143SlopeStabilityAnalysisTheevaluationmethodsofslopestabilitycanbesummarizedintothreetypes:(1)engineeringgeologicalanalysismethod;(2)theoreticalcalculationmethod(formulacalculation,diagramandnumericalanalysis);(3)testandobservationmethods.(1)EngineeringgeologicalanalysismethodThemostimportantelementoftheengineeringgeologicalanalysismethodistheanalogicalmethod,whichisthemostcommonandpracticalmethodofslopestabilityanalysisinproductionpractice.Inpracticalengineering,itisalsocommontoestablishanempiricalformulatodeterminethestabilityofslopesthroughalargenumberofstatisticalanalyses.Theempiricalformulaforthestabilityslopeofgeneralroadrockslopesestablishedisasfollows:153SlopeStabilityAnalysis(2)MechanicalcalculationmethodThemechanicalcalculationofslopestabilityisawidelyusedmethodforderivingquantitativeexpressionsofstabilityandisoftennecessaryforengineeringpurposes.AnalysismethodsforstabilityofsoilcuttingslopeForslidingfailureonsoilcuttingslopes,stabilitycalculationscanbecarriedoutbasedontheanalysisoftheaboveinfluencingfactors.Differentstabilitycalculationmethodscanbeusedfordifferentslipsurfaceshapes.CalculationofstabilityofsoilslopeswhentheslipsurfaceisflatSlopesmadeupofhomogeneoussandyorpebblysoils,etc.andslopesmadeupoflayersofnon-homogeneoussandysoils,haveanearlyflatslidingsurfacewhenfailure.163SlopeStabilityAnalysis(2)MechanicalcalculationmethodAnalysismethodsforstabilityofsoilcuttingslopeII.StabilitycalculationsforsoilslopeswithcircularslidingsurfacesAccordingtoalargenumberofobservations,theslidingsurfaceofacohesivesoilslopeissimilartoacylindricalsurfacewhenslidingfailureoccurs,andcanberegardedasacirculararcinthesection,calledasliparc.Themethodoftenusedtocalculatethestabilityofaslopewithacircularslidingsurfaceisthestripdivisionmethodinsoilmechanics.173SlopeStabilityAnalysis(2)MechanicalcalculationmethodAnalysismethodsforstabilityofsoilcuttingslopeIII.SwedishmethodTheearliestandsimplestmethodofbarsplittingistheSwedishArcMethod(SAM),alsoreferredtotheSwedishmethodorFelleniusmethod.Thebasicassumptionsare:Thesoilstabilityisaplanarstress-strainissue,whichonecertaincross-sectioncouldbeanalyzedastheexample.thefailurezoneofsoilisacylindricalsurfaceandslidingsurfaceofthecross-sectionoccurasanarc.Inaddition,slipmassisconsideredasrigidwithoutinteractionforcebetweenslices.SchematicillustrationoftheFelleniusmethod183SlopeStabilityAnalysis(2)MechanicalcalculationmethodAnalysismethodsforstabilityofsoilcuttingslopeIII.SwedishmethodTheempiricalformulaisasfollows:where:Wi－weightofsoilcolumnαi－bottominclinationofsoilcolumnli－bottomarclengthofsoilcolumnui－porewaterpressureontheslipsurfaceciandϕ－IndexoftheeffectiveshearstrengthSchematicillustrationoftheFelleniusmethod193SlopeStabilityAnalysis(2)MechanicalcalculationmethodAnalysismethodsforstabilityofsoilcuttingslopeIV.BishopmethodDifferenttotheFelleniusmethod,adevelopedmethodforevaluatingtheslopestabilitynamedBishopmethodconsidersthehorizontalinteractionforcebetweenthesoilcolumns.ThefactorofsafetyKcanbecalculatedasfollows:WhereQiisweightofsoilcolumnhorizontalresultantforcebetweensoilcolumns,othersymbolsarethesameasbefore.SchematicillustrationoftheBishopmethod203SlopeStabilityAnalysis(2)Mechanicalcalculationmethodb)AnalysismethodsforstabilityofsoilcuttingslopeI.StabilityofplanarfailurePlanarfailurealwaysoccursonthesinglestructuralplaneandgeometrywascharacterizedbythestructuralplanedipoutsidetheslopeandadip-anglelessthantheslopeangle.TheFactorofsafetyKcanbecalculatedasfollows:Schematicillustrationforplanarfailureofarockslope213SlopeStabilityAnalysis(2)Mechanicalcalculationmethodb)AnalysismethodsforstabilityofsoilcuttingslopeII.StabilityofwedgefailureWedgefailureisakindofcuttingblockarousedbytwogroupsofstructuralplanesaswellasslopesurface.TheFactorofsafetyKcanbecalculatedasfollows:where:ϕ1andϕ2－frictionanglesontwoslipsurfaces,respectivelyc1andc2－cohesionontwoslipsurfaces,respectivelyα－dipangelofthelineintersectedbytwoslipsurfacesL－lengthofthelineintersectedbytwoslipsurfacesSchematicillustrationforwedgefailureofarockslope224CountermeasureforPreventingSlopefailureAtpresent,therearethreemaintypesofengineeringmeasurestoincreasethestabilityofslopes:improveslopeengineeringgeologicalconditions;passivereinforcementmeasures;andactivereinforcementmeasures.(1)ImprovingtheengineeringgeologicalconditionsofslopesThiskindofengineeringmeasuresmainlyimprovethestabilityofslopebychangingtheshapeofacoastalslope(suchasslowingslope,cuttingandreducingload,backpressureofpileload,etc.),hydrogeologicalconditions,geotechnicalphysicalparametersandvegetationconditions,forexample.Schematicillustrationofloadingandgrading234CountermeasureforPreventingSlopefailure(2)PassivereinforcementmeasuresThistypeofreinforcementcannotactivelyexertforcesontheslope,butreliesonitsowngravityoritsembeddednessinthegeotechnicalbodytoresisttheresidualslidingforcesorearthpressureofthegeotechnicalbody.Thistypeofreinforcementcanonlyplayareinforcingrolewhenthegeotechnicalbodyoftheslopeisdeformed,soitiscalledpassivereinforcement.Anti-slipretainingwallsAccordingtothenatureandtypeofslidingandtheforcecharacteristics,materialandstructureoftheanti-slipretainingwall,theanti-slipretainingwallisdividedintogravity-typeanti-slipretain