Geology Applied to Civil Engineering 土木工程地質(zhì) 英文課件 第八章 Rockfall and Landslide

18.1RockfallandLandslideGeologyAppliedtoCivilEngineering123contentsStabilityevaluationofunstablerockStructuralcountermeasureforrockfallConcept,formationandclassificationofrockfall4Conceptandmorphologicalcharacteristicsoflandslides5Formationandclassificationoflandslides6Fieldidentificationandstabilityevaluationoflandslides231Concept,formationandclassificationofrockfallRockfalls,asoneofthecommontypesofgeologicalhazardsinmountains,coasts,trafficcorridorsandopencastquarries,havethecharacteristicsofwidedistribution,suddenfailure,concealmentandseverity.Fourcharacteristicsofrockfalls:(1)themovementofrockfallsdoesnotoccuralongafixedplaneorzone;(2)thefierceimpactonthegroundcancausetheoriginalintegrityofdetachedrockmassescompletelydestroyedandthereforethestructureoftaluswouldbeloose,indisorder,unstratifiedandporous;(3)thesmallerfragmentscantravellongerdistancecomparedtothelargerones,resultinginacertaindegreeofsortinginthehorizontaldirection;(4)theverticaldisplacementofrockfallsisgreaterthanthehorizontalone.Sortingoffragmentsofafallingrockfromimpactpointtomargin41Concept,formationandclassificationofrockfallGeomorphiccondition:rockfallsusuallyoccuronthesteepslopeofavalley,attheconcavebankofariveroragully,atthesteepcliffofacoastline.Stratigraphic&lithologicalcondition:ingeneral,alarge-scalerockfallispronetodevelopinthehardrocksuchasmagmaticrocks,metamorphicrocksandsedimentaryones(carbonaterock,quartzsandstone,conglomerate).Tectonicconditions:whentherailwaylineisparalleltoandnearbytheregionalfault,rockfallsontheexcavatedslopearewidespreadandseriousbecauseofthegreatgeostressanddensestructureplanes.51Concept,formationandclassificationofrockfallHydrogeologicalconditions:thegroundwaterandinfiltratedsurfacewaterinthecrackscanpromotetheoccurrenceofrockfalls.Earthquake:duringanearthquake,thestrongvibrationcanreducetheshearstrengthofstructuralplanesanddamagethestructureofrockmasses.Additionally,undergreatseismicforce,thestabilityoftheunstablerockwillgreatlydecrease.Weathering:underthelong-termactionofweathering,thestrengthandstabilityofrockmassesontheslopeareconstantlyreduced,whichfinallyleadstotheoccurrenceofrockfalls.Humanactivities:theanthropogenicinfluencesonrockfallsmainlyrefertotwoaspects:unreasonabledesignandimproperconstructiontreatment.61Concept,formationandclassificationofrockfallToppling-fall:theunstablerockcanturnaroundacertainpointatthetoeduetothebiaspressureorlateralpush.Onthesteepslopesofthevalley,loessplateau,karstareaandexcavationarea,thereareoftenhugeanduprightrockpillarsseparatingfromstablebedrockbyverticaljointsorcracks.Thiskindofunstablerockmasseshavealongcolumnarshapeandpoorlateralstability.Ifthetoeoftheunstablerockiscontinuouslydamagedanderoded,itwillgraduallytiltundertheactionofgravityandeventuallytopple.Moreover,ifthereisalargehorizontalforce,suchasseismicforce,hydrostaticpressure,hydrodynamicpressureandfrostheaveforce,theunstablerockcansuddenlytoppleandcollapse.crack(a)(b)Topplingfailureofanunstablerock:(a)verticalunloadingcrackseparatingtheunstablerockfrombedrock;(b)schematicdiagramoftoppling-fall.71Concept,formationandclassificationofrockfall(2)Sliding-fall:iftherearesmoothstructuralplanesorweakinterlayersatthebottomoftheunstablerockincliningoutwardtheslope,theunstablerockcouldslidefirstandthencollapseundertheconditionofrainfall,earthquakeorotherdisturbances.Theslidingplaneisusuallyevolvedfromthebeddingplane,jointortheunconformablecontactplane.Oncegravitycenteroftheunstablerockslidesoutoftheslope,asuddenfallingwilloccur.

(a)(b)(c)Slidingfailureofanunstablerock:(a)anunstablerockslidesalongthebeddingplane;(b)schematicdiagramofaplanarsliding-fall;(c)schematicdiagramofaslump-fall.8(3)Distending-fall:ifthereisasoftstratumbeneathathickhardone,thesoftrockcouldcontinuouslydeformunderthecompressionoftheupperhardrock.Whenthecompressivestressexceedsthecompressivestrengthofthesoftrock,thesoftonewillbefracturedandsqueezedout.Inparticular,theheavyprecipitationorthegroundwaterfluctuationcanincreasetheweightoftheupperrockandsoftenthelowersoftrock,resultinginarapiddistending.Withthesoftrockdistendinganddamaging,theupperhardrockcouldsink,slideandtiltatthesametime.Finally,oncethecenterofgravityoftheunstablerockmovesoutoftheslope,rockfallwilloccur.1Concept,formationandclassificationofrockfalllimestonedistendingmudstone(a)(b)Distendingfailureofanunstablerock:(a)thesoftmudstonelayerdistendingoutward;(b)schematicdiagramofdistending-fall91Concept,formationandclassificationofrockfall(4)Splitting-fall:iftherearelargecavitiesinthesteepslopeformedbydifferentialweatheringofsoftandhardrockstrata,manualexcavation,rivererosion,aeolianerosion,rootandicecleavage,theupperrockprotrudesintheformofcantileverbeams.Ifthetensilestressoftheprotrudingrockisgreaterthanitstensilestrength,thetensilecrackswilldeveloprapidlyuntiltheoccurrenceofrockfalls.sandstonemudstone(a)(b)Splittingfailureofanunstablerock:(a)cavitiescausingtherocksuspendingpartially;(b)schematicdiagramofsplitting-fall101Concept,formationandclassificationofrockfall(5)Rupturing-fall:forunstablerockslocallyseparatingfromthestablebedrockbyverticaljointsorcracksbutconnectingthebedrockbyintactrockbridges,therupturingoftherockbridgesisthekeypointofthestabilityoftheunstablerocks.Generally,whentheweightoftheunstablerocksincreasesbyprecipitationorsnowmeltingorthevolumeoftherockbridgedecreasesbymanualexcavation,theunstablerockswillcollapse.Inotherwords,oncetheshearstressoftherockbridgeisgreaterthanitsshearstrengthorthetensilestressisgreaterthanthetensilestrength,rockfallwouldoccurimmediately.However,inactualengineering,therupturingofarockbridgeisrarecomparedwiththetopplingandsplittingfailures.dolomiterockbridge(a)(b)Rupturingofrockbridgeofanunstablerock:(a)anunstablerockpostingonasteepslope;(b)schematicdiagramofrupturing-fall112StabilityevaluationofunstablerockSliding-falla)single-planesliding:theslidingforceisthetangentialcomponentoftheweightWoftheunstablerock.Underearthquakeconditions,theshearforceiscomposedofthetangentialcomponentoftheweightWandhorizontalseismicforceQ(Fig.8-12).TheresistanceforceiscomposedofthefrictionandthecohesionalongtheACslidingplane.ThehydrostaticpressureofwaterVinthecrackdependsonthefillingheightofwaterhw.Thestabilitycoefficientoftheslidingrockis

Calculationmodelofanunstablerockwithaslidingfailure122StabilityevaluationofunstablerockSliding-fallb)wedgesliding:thewedge-shapedunstablerockislocatedontheslopewiththegradientofαandtheheightofH.ThestructureplanesABDandBCDarecompletelysymmetricalwiththeverticalplaneasthesymmetryplane.Oisthecenterofgravityofthewedgerock.βisthedipoftheintersectionlineBD.c1andφ1arethecohesionandfrictionangleofplaneABD,respectively.c2andφ2arethecohesionandfrictionangleofplaneBCD,respectively.Thestabilitycoefficient(K)canbecalculatedaswhere:and(a)(b)(c)Calculationmodelofanunstablerockwithwedgeslidingfailure:(a)three-dimensionalmodel;(b)cross-sectionalprofile(B-D);(c)thenormalpressuresonthestructuresandintersectionline.132Stabilityevaluationofunstablerock(2)Toppling-falla)WhenthecenterofgravityoftheunstablerockislocatedwithinthelineCD,theoverturningmomentisprovidedbyhydrostaticpressureoffissurewaterVandhorizontalseismicforceQunderearthquakecondition,andtheanti-overturningmomentisprovidedbytheweightoftheunstablerockWandthetensilestrengthoftherockonthelineBC.Inthiscase,thestabilitycoefficientofthetopplingrockisCalculationmodelofanunstablerockwithtopplingfailure142Stabilityevaluationofunstablerock(2)Toppling-fallb)WhenthecenterofgravityoftheunstablerockislocatedoutsidetheoverturningpointDandwithinthelineDE,theoverturningmomentisgeneratedbyweight,hydrostaticpressureoffissurewaterandhorizontalseismicforce,andtheanti-overturningmomentisgeneratedbythetensilestrengthoftherockonthelineBC.Inthiscase,thestabilitycoefficientofthetopplingrockisexpressedinequation8-8.ThecalculationparametersareCalculationmodelofanunstablerockwithtopplingfailure152Stabilityevaluationofunstablerock(3)Splitting-fallWhenthetensilestressofrockbridgeisgreaterthanitstensilestrength,thecrackwilldeveloprapidlyandtherockfallwilloccur.Significantly,asthedrainageofthecrackisunobstructed,thehydrostaticpressureoffissurewaterisnotconsidered.Becausethecompletelyseparatedrockcouldeitherslideortopplesequentially,thestabilitycoefficientoftheunstablerockcanbecalculatedbyforslidingfailure:fortopplingfailure:Thecalculationparameters:Calculationmodelofanunstablerockwithtensilesplittingfailure163StructuralcountermeasureforrockfallActiveprotectivemeasure:if1)thescale,impactforceandimpactenergyoffallingrocksareextremelyhighor2)thepassivemeasurescannotbeimplementedorhavenoeffect,theactivemeasuresshouldbeconsidered.Removingunstablerockmasses:ifthenumberofunstablerocksissmallandthebedrockisintactandhard,itisadvisabletoremovealltheunstablerocks.Drainageofexcessivewater:surfacewaterandgroundwaterareusuallythecausesofrockfalls.Theusualdrainagestructuresareinterceptinganddivertingthesurfacewater,dischargingthefissurewaterandblockingseepagepath.Reinforceorsupport:theusualreinforcementmeasuresincludeanchorcable,anchorbolt,supportingwallandactivenet,whichshouldbeselectedbasedonthetopographyoftheslope,thescaleandtheinstabilitymodeoftheunstablerock.Passiveprotectivemeasure:ifactiveprotectivemeasurescannotbeappliedandtheimpactforceandpowerofunstablerocksareassessedtobesmall,thepassiveprotectivemeasurescanbearrangedatthefootoftheslope.173Structuralcountermeasureforrockfall(6)Retainingwall:forabundantunstablerocksofthehighlyweatheredslopewithsmall-scaleandfrequentoccurrence,interceptingstructurescanbeinstalledatthetoeorgentleareasoftheslope,suchasrockfallplatform,rockfallgrooveandretainingwall.(7)Passivenet:forasmall-scalerockfallwhosetrajectoryandstoppingpositioncanbedetermined,theSNSflexiblepassiveprotectionsystem(referredtoas"passivenet")canbeusedinthegentlezoneatthewaistortoeoftheslope.(8)Rockshed:ifthelocationoftheunstablerocksisveryhigh,theslopeisverysteepandtheconstructionofanactiveprotectivestructureisextremelydifficult,rockshedcanbeusedduetoitsstrongimpactresistanceandhugeprotectionspace.MasonryretainingwallPassivenet184ConceptandmorphologicalcharacteristicsoflandslidesLandslideisgeologicalphenomenonthatrock-soilmassesofartificialornaturalslopesmovedownwardalongoneormoreweakplanesorzonesunderthegravity,affectedbyrainfall,groundwater,rivererosion,earthquake,humanactivitiesandotherfactors,oncetheshearforceisgreaterthantheshearresistance.Slidingmasscanbedividedintosoil,rock,oramixtureofthetwo,anditmaybreakapartduringmovementorremainintact.Foracompletelyevolvedlandslide,themorphologicalandstructuralcharacteristicsareobvious.Suchsignificantsymbolsareveryusefultoaascertainlandslideduringthefieldsurvey.Typicalmorphologicalcharacteristicsofaslumporrotationallandslide1:slidingbody;2:slidingplane(slidebelt);3:landslidebed;4:landslideboundary;5:scarp;6:landslideplatform;7:trappeddepression;8:landslidetongue;9:landslidecrack;10:themainslidingline(landslidespindle);11:toeofsurfaceofrupture195FormationandclassificationoflandslidesGeomorphicconditions:theheight,gradientandmorphologyhaveacloserelationshipwiththestabilityofslopes.Thecanyonareas,theedgesofbasins,theconcavebanksofbigriversandthebanksoflargereservoirsarepronetolandslidewhentheareassufferfromearthquake,rainstorm,waterlevelfluctuationandartificialblasting.Inaddition,thegravitationaldeposits,residualdeposits,alluvialdeposits,diluvialdeposits,rocktalus,ancientlandslidesandartificialspoilongentlehillslopescouldslideunderthescouringanderosionofsurfacewaterandgroundwater.(2)Stratigraphic&lithologicalconditions：stratigraphiclithologyisthematerialbasisoflandslides.Statistically,landslidesarepronetooccurinthefollowingstratigraphiclithologygroups.claygroup;siltsoilgroup;sedimentaryrockgroup;metamorphicrockgroup.205Formationandclassificationoflandslides(3)Tectonicconditions:thetectonicmovementcanproduceaweakgeologicalstructuresincludingfaultplanes,interlayerstaggeredzones,joints,schistosityplanesandunconformitysurfaces.Suchweakstructureplanesnotonlycontrolthespatiallocationandboundaryoftheslidingplane,butalsodeterminethedistributionandmovementofgroundwaterinlandslides.(4)Hydrogeologicalcondition：thegroundwaterandinfiltratedsurfacewatercancausetheunstablerockandsoilmassestobecomealandslide.Sincegroundwaterandsurfacewaterareallreplenishedbyrainfall,therainfallisasignificanttriggeroflandslides.(5)Humanactivities:withthegrowthofpopulationandtheconstructionofhumaninfrastructures,moreandmorehuman-inducedlandslidesareoccurring.215FormationandclassificationoflandslidesClassificationbasedonthemorphologyoftheslidingplaneTheslidingplaneisplanar,curvedorpolygonal.Normally,rockslideshaveaplanarslidingplane,whichiscomposedofthebeddingplane,theweakinterlayersortheunloadingandweatheringcrack.Theslidingplaneoflandslidesinhomogeneouscohesivesoil,namelyslumpsorrotationallandslides,isalwayscurved.Soil-rockmixedlandslidesandthejoints-cutrockslidesoftenhavepolygonalslidingplanes.(2)ClassificationbasedonthethicknessofslidingmassesWhenthethicknessofthelandslidebodyistoolarge,avoidanceandevacuationshouldbeconsideredfirst.Theclassificationbasedonthethicknessoflandslidesareverythick(>50m),thick(20-50m),moderate(6-20m)andthin(<6m).(3)ClassificationbasedonthevolumeofslidingmassesTheclassificationbasedonthevolumeoflandslidesaregiantlandslide(>10millionm3),largelandslide(1-10millionm3),mediumlandslide(0.1-1millionm3)andsmalllandslide(<0.1millionm3).225Formationandclassificationoflandslides(4)ClassificationbasedonthevelocityoflandslidesTheclassificationbasedonthevelocitiesoflandslidesarecreepinglandslide(movementcanbeonlydetectedbymonitoring);slow-speedlandslide(afewcentimeterstotensofcentimetersperday,canbeobservedwithnakedeyes);medium-speedlandslides(tensofcentimeterstolessthan5metersperhour)andhigh-speedlandslides(morethan5meterspersecond).(5)ClassificationbasedonthematerialcompositionoflandslidesThelandslidescomposedofvariousmaterialsiscompletelydifferentinfailuremode,movementanddepositioncharacteristics.Generally,thetypesoflandslidematerialsmainlyincludedeposit,loess,clayandbedrock.Thecorrespondinglandslidetypesare:depositlandslide,loesslandslide,claylandslide,androckslide.235Formationandclassificationoflandslides(6)ClassificationbasedonthetriggersLandslideinducedbyendogenicgeologicalprocess;Landslideinducedbyexogenicgeologicalprocesses.(7)ClassificationbasedonthemechanicalcharacteristicsRetrogressivelandslide;Progressivelandslide;Translationallandslide;Compositelandslide.(a)(b)MassiveDaguangbaolandslidewithavolumeof11.99×108m3:(a)themainscarpandrightflankofthelandslide;(b)landslidedeposits.246FieldidentificationandstabilityevaluationoflandslidesThereareaplentyoffieldevidencesthatcanhelpustoidentifylandslidesduringthegeologicalsurvey.Geomorphologicalevidences:Chair-shapedsteepescarpmentisatypicalcharacteristicofthemainscarpoflandslides.Thetoeofthelandslidecanpossiblyplungeintotheriverandblockit.Inaddition,thelateralboundariesoflandslidesusuallydevelopedastwodeepgullieswiththesameoriginatthetop.EvidencesofstratigraphicandgeologicalstructuresThesignificantchangesofoccurrenceandcontinuitiesofthegeologicalstructurecanbeusedtoidentifylandslides.c)HydrogeologicalevidencesGenerally,thehydrogeologicalconditionofthelandslideisquitedifferentfromtheoriginalslope,whichcanbetreatedasanindividualwater-bearingbody.“Drunk”treesincliningtowardsdifferentdirectionsAnancientlandslidewithtwodeep-cuttinggulliesasboundaries256FieldidentificationandstabilityevaluationoflandslidesStabilityevaluationoflandslides:thestabilitycoefficientKisregardedasanimportantindexforthestabilityevaluationofaslopeindifferentstages,whereKisreferredtotheformulaTheslidingbodyshouldbedividedintomanyverticalslices(from1ton)onthecross-sectionprofilewhilecalculatingthestabilitycoefficient.Correspondingly,thestabilitycoefficientKofthelandslidewithpolygonal-shapeslidingplanecanbeexpressedinthefollowingequation:where:Calculationdiagramofthestabilitycoefficientofthelandslide:(a)verticalslicesoftheslidingbody;(b)analysisofloadinandoutofaverticalslice.Ei-1isthepressureofslicei-1onsliceiandEiisslicei+1onslicei.266FieldidentificationandstabilityevaluationoflandslidesMitigationandControlMeasures:a)AvoidingthelandslidehazardForthelarge-scalelandslideorlandslidesingroup,duetothehugequantity,highcostandlongperiodofthemitigationengineering,itisbettertoavoidthehazard-impactedareaduringthereconnaissanceanddesignperiod.b)ImprovementofthegeologicalconditionTheimprov