英語(yǔ)翻譯-植被模型對(duì)邊坡穩(wěn)定性的影響

河北工程大學(xué)本科畢業(yè)設(shè)計(jì)英語(yǔ)翻譯譯文題目：ModellingtheEffectsofVegetationonStabilityofSlopes植被模型對(duì)邊坡穩(wěn)定性的影響姓名：專(zhuān)業(yè)：勘查技術(shù)與工程班級(jí)學(xué)號(hào)：指導(dǎo)老師：指導(dǎo)教師職稱(chēng)：教授2013年6月12日ModellingtheEffectsofVegetationonStabilityofSlopesSummary:Itiswellunderstoodthatvegetationinfluencesslopestabilityintwoways:throughhydrologicaleffectsandmechanicaleffects.Hydrologicaleffectsinvolvetheremovalofsoilwaterbyevapotranspirationthroughvegetation,whichleadtoanincreaseinsoilsuctionorareductioninpore-waterpressure,hence,anincreaseinthesoilshearstrength.Theshearstrengthofthesoilisalsoincreasedthroughthemechanicaleffectsoftheplantrootmatrixsystem.Thedensityoftherootswithinthesoilmassandtheroottensilestrengthcontributetotheabilityofthesoilstoresistshearstress.Theeffectsofsoilsuctionandrootreinforcementhasbeenquantifiedasanincreaseinapparentsoilcohesion.Thispaperinvestigatestheeffectsofvegetationonthestabilityofslopesusingthefiniteelementmethod.Twokeyvegetation-dependentparametershavebeenincorporatedinthefiniteelementslopestabilityanalysis,namely,apparentrootcohesion(CR)anddepthofrootzone(hR).Parametricstudieswereperformedtoassessthesensitivityofthestabilityofaslopetothevariationinthekeyvegetationandsoilparameters.Resultsshowthatvegetationplaysanimportantroleinstabilizingshallow-seatedfailureofslopes,andsignificantlyaffectsstability.INTRODUCTIONSlopeinstabilityisoneofthemajorproblemsingeotechnicalengineeringwheredisasters,likelossoflifeandproperty,dooccur.Themajorityoftheseslopefailuresareofvegetatedorforestednaturalslopes.Anaturalslopeisdifferentfromanembankmentoraman-madeslopeinthattheeffectsofvegetationandsoilvariabilityplayanimportantroleintheirstability.Theeffectsofvegetationonthestabilityofslopesarewellrecognized.Vegetationaffectsslopestabilitythroughmodificationofthesoilwaterregime,whichinturncausesavariationinsoilsuctionorporepressure.Vegetationcanalsoenhancethestabilityofaslopebyrootreinforcement.Wuetal.(1979)investigatedthestabilityofslopesbeforeandafterremovalofforestcoverandconcludedthattheshearstrengthcontributedbytreerootsisimportanttothestabilityofslopes.Thestudyindicatedthatvegetationcouldcontributeshearstrengthtotheslopesthroughrootreinforcement.Wuetal.(1979)showedthatslopefailurewouldhaveoccurrediftheeffectsofvegetationwerenottakenintoaccountinslopestabilityanalyses.Naturalslopesaresubjectedtoinherentvariabilitybothinthesoilandthevegetation.Itisunlikelythattheunderlyingsoilprofilesofnaturalslopesarecompletelyuniformorhomogenous.Evenwithinahomogenoussoillayer,soilpropertiestendtovaryfrompointtopoint(Vanmarcke,1977).Thegrowthofvegetationissensitivetoenvironmentalconditionsandchanges.Typicallydifferenttypesofvegetationgrowonanaturalslope,suchasamixtureofgrasses,herbs,scrubsandtrees.Theirdifferencesinsizeandphysicalpropertieswillaffecttheslopestabilityindifferentways.Therefore,theuseofasingleinputvalueforthevegetation-dependentparametersinanalysesisbestviewedasafirstapproximationofthefieldconditions.Thispaperinvestigatestheeffectsofvegetationonthestabilityofslopesusingthefiniteelementmethod.Thefiniteelementmethodallowstheextentofthevegetationeffectstobedefinedbytheuserduetothenatureofthemethodwhereslopegeometryisdicretisedintosmallelements.Tolimitthescopeofthispaper,onlytheeffectsofrootreinforcementareincorporatedintheslopestabilityanalysis.Thevariabilityinthevegetationandsoilpropertiesarenotconsideredinthispaper.A2:1homogenousslope(angleofinclination26.57°)isusedtoinvestigatetheeffectsofvegetationonslopestability.Twokeyvegetation-dependentparametersareincorporatedinthefiniteelementslopestabilityanalysis,namely,apparentrootcohesion(cR)anddepthofrootzone(hR).Parametricstudieswereperformedtoassessthesensitivityofthestabilityoftheslopetothevariationinthekeyvegetationandsoilparameters.PREVIOUSANALYSESOFTHEEFFECTSOFVEGETATIONONSLOPESTABILITYModelofRootReinforcementForthepastthreedecades,researchhasfocusedonutilizingplantrootreinforcementtostabilizeslopes.Theabilityofplantrootstostrengthenasoilmassiswellknown.Theinclusionofplantrootswithhightensilestrengthincreasestheconfiningstressinthesoilmassbyitscloselyspacedrootmatrixsystem.Thesoilmassisboundtogetherbytheplantrootsandtheshearstrengthisincreasedbythiseffect.Thecontributionofrootreinforcementtoshearstrengthisconsideredtohavethecharacteristicsofcohesion(Wuetal.,1979).Wuetal.(1979)proposedasimplifiedperpendicularrootmodeltoquantifytheincreasedshearstrengthofsoilduetorootreinforcement.Theincreaseinshearstrengthofthesoil,Sr,wasexpressedbythefollowingrelationship:Sr=tR(cosθtanφ′+sinθ)(1)whereSr=shearstrengthincreasefromrootreinforcement,tR=averagetensilestrengthofrootperunitareaofsoil,θ=angleofshearrotation,andφ′=frictionangle.Sincethemechanicaleffectofplantrootsistoincreasethecohesivenessofthesoilmass,Srcanbeconsideredasequivalenttoanapparentcohesionofthesoil,knownasapparentrootcohesion(cR).Typicalvaluesofapparentrootcohesion(cR)rangefrom1kPato17.5kPa(CoppinandRichards,1990).Thesevalueswereobtainedfromthestudiesofseveralinvestigatorsusingdifferenttechniquesincludingbackanalysis,directsheartests,rootdensityinformationcombinedwithverticalrootmodelequations,andbackanalysiscombinedwithrootdensityinformation.Thevaluesofapparentrootcohesion(cR)aredependentonthetypeofvegetationandin-situsoilconditions.PreviousSlopeStabilityAnalysesWuetal.(1979)incorporatedtheeffectsofvegetationinslopestabilityanalysisbyusingconventionallimitequilibriummethod.Inlimitequilibriummethods,theshearstrengthofthesoilalongapotentialslipsurfaceisassumedtobefullymobilizedatthepointoffailure.TheMohr-Coulombequationisusedtodescribetheshearstrengthofthesoil:τ=c′+(σ-u)tanφ′(2)Byincorporatingtheeffectofrootreinforcement,Equation(2)becomes:τ=(c′+cR)+(σ-u)tanφ′(3)Wuetal.(1979)incorporatedtheapparentrootcohesion(cR)intheirinfiniteslopeanalysisandfoundanincreaseinthefactorofsafety(FOS)forsomeslopes.Theresultsindicatedthattreerootsimprovedthestabilityofforestedslopes.Therehavebeennopublishedstudiesusingnumericalformulationstoanalyzerootreinforcementeffects.Thepresentstudyemploysnumericalanalysiswhichallowslimitingtheextentoftherootzone.Byassigningdifferentvaluesofapparentrootcohesion(cR)totherootzone,itssignificanceontheFOSisevaluated.DESCRIPTIONOFNUMERICALSTUDYUSEDTOMODELVEGETATIONEFFECTSInthepresentstudy,theeffectofvegetationonthestabilityofslopeshasbeeninvestigatedusingthefiniteelementmethod.Thediscretisationprocessofthefiniteelementmethodbreaksdowntheslopegeometryintosmallelementsandthisfacilitatestheincorporationoftheeffectsofvegetationintheslopestabilityanalysis.Theeffectsofvegetationaretakenintoaccountintheslopestabilityanalysisbymodifyingthesoilpropertiesoftheindividualsoilelementthatisaffectedbyvegetation.Forexample,thesoilelementsinthetoplayeroftheslopecanhaveahighercohesionvalueduetotheadditionalapparentcohesionfromrootreinforcement.Variationofsoilsuctioncausedbyvegetationcanalsobeincorporatedinthefiniteelementanalysis.Theflexibilityinlocatingthevegetation-affectedelementsmeansthatthevariableandrandomnatureofvegetationcanbemodeledeffectively.Inthispaper,theworkislimitedtotheeffectsofrootreinforcementonthestabilityofslopes.TheFiniteElementModelThefiniteelementmodelinthepresentstudyassumes2-dimensionalplanestrainconditions.TheprogramusedinthisstudywasdevelopedbySmithandGriffiths(1998)andituseseight-noddedquadrilateralelements.Anelasto-plasticmodelwithMohr-Coulombfailurecriterionisassumed.Thisprogramhasbeenusedtoanalyzeseveralslopestabilityproblemsincludingtheinfluenceoflayeringandfreesurfaceonslopeanddamstability(GriffithsandLane,1999).Theprogramcomputesthefactorofsafety(FOS)oftheslopebyusingthenonconvergencesolution,coupledwithasuddenincreaseinnodaldisplacementsasanindicationoffailureconditions(GriffithsandLane,1999).Inthisstudy,a2:1homogenousslope(26.57°)withaheightof10metresisusedtoinvestigatetheeffectsofvegetationonthestabilityofaslope,asshowninFigure1.Thesoilpropertiesareasfollows:φ′=25°c′=0γ=20kN/m3Twoadditionalvegetation-dependentparametersusedintheslopestabilityanalysisareapparentrootcohesion(cR)anddepthofrootzone(hR).Apparentrootcohesion(cR)istheapparentsoilcohesioncausedbytheplantrootmatrixsystem.Thedepthoftherootzone(hR)isdefinedastheeffectivedistancebeyondwhichplantrootscauselittleornoeffectsonthesoilshearstrength.Twoscenariosareconsidered:(1)vegetationconfinedtotheslopesurfaceonly;and(2)vegetationextendingovertheentiregroundsurface.Parametricstudiesareperformedtoassessthesensitivityofthestabilityoftheslopetothevariationinkeyvegetation-dependentparameters.Figure1.Meshfora2:1HomogenousSlopewithaSlopeAngleof26.57°,φ′=25°,c′=0.RESULTSOFANALYSESSlopewithoutVegetationEffects(c′=0,cR=0)Thestabilityofthe2:1homogenousslopewithoutvegetationwasanalysedusingboththefiniteelementmethodandthelimitequilibriummethod.ThelimitequilibriummethodwasperformedusingtheGGU-Stabilityprogram(Bu?,1999)whereBishop’ssimplifiedmethodofsliceswasadopted.TheresultsoftheanalysesaresummarisedinTable1.Table1.FactorofSafetyfortheSlopeUsingDifferentMethods.METHODFOSFiniteElementMethod0.95LimitEquilibriumMethod0.93TheresultsinTable1showthatbothmethodsgivecomparableresults,althoughthelimitequilibriummethodgivesaslightlylowervaluecomparedtothefiniteelementmethod.Figure2showsthedeformedfiniteelementmeshoftheslopeatfailure,andthecorrespondingFOS=0.95.Itcanbeobservedthatthefailuremechanismisashallowplanarfailure.Thefailureoccurswithinthefirsttwolayersoftheelements,extendingto2metersbelowtheslopesurface.Figure2.DeformedMeshatFailurefortheSlopewithc′=0.SlopewithVegetationEffects(c′=0,cR=5kPa,hR=1m)Case1–VegetationConfinedtotheSlopeSurfaceOnlyThefirstcaseinvolvesascenariowherevegetationgrowsontheslopesurfaceonly.Thehorizontalgroundsurfaces,ontheslopeitselfaswellasbeyondtheslopetoe,arenotcoveredbyvegetation.Theeffectofrootreinforcementisconsideredbyusingapparentrootcohesion(cR)of5kPa.Thedepthofrootzone(hR)isconsideredtobe1metre.Accordingly,thezonemodelledwiththeadditionalrootstrengthisconfinedtothefirstlayerofthefiniteelementsbeneaththeslopesurface.Thus,thefirstlayerofelementsinthefiniteelementmodel,shownasshadedinFigure3,hasahighervalueofsoilcohesioncomparedtoallotherelementsinthefiniteelementmesh.TheslopestabilityanalysisgavearesultofFOS=0.97.ThedeformedmeshoftheslopeatfailureisshowninFigure3.Sincetheslopeisprotectedbyvegetationontheslopesurfaceonly,failurewas,inthiscase,initiatedfromtheslopetoe(elementT).Afailureslipsurfacethendevelopedalongthesoillayerbeneaththerootzone,asthissoillayeristhetopoftheweakzoneintheslopeafterintroducingarootzone.AlthoughtheincrementintheFOSissmall,itcanbenotedfromFigure3thatthecriticalslipsurfacehasbeenshifteddeeperbelowthegroundsurface,beinglocatedbetweenthesecondandthirdlayersofthefiniteelements.Theshallowplanarfailureattheslopesurfaceisnolongercritical,becauseofthepresentoftherootzone.Whentheslopetoeelement(elementTinFigure3)istreatedasavegetatedsoilelement(assignedhigherapparentcohesion),theFOSfortheslopeincreasesto1.02.Thisshowsthattoefailureisthecriticalfailuremechanismforthecasewherevegetationisconfinedtotheslopesurfaceonly.TheincreaseintheFOSisnotsignificantiftheslopetoeisnotvegetated.Therefore,theextentoftherootzonetotheslopetoeregionisanimportantfactortobeconsideredwhenvegetationisusedtoimprovethestabilityofaslope.Figure3.DeformedMeshatFailurefortheSlopewithVegetationonSlopeSurfaceOnly(c′=0,cR=5kPa,hR=1m).Case2–VegetationExtendingOvertheEntireGroundSurfaceAmorecommonscenarioinnaturalslopesisthecasewherevegetationgrowseverywhereonthegroundsurface,whichextendsfromtheuppersloperegiontotheslopetoe.Similarly,anapparentrootcohesionof5kPaanddepthofrootzoneof1metrewereadopted.Inthiscase,therootreinforcementeffectextendseverywhereonthegroundsurfaceinthefiniteelementmodel,asshowninFigure4.ThefiniteelementanalysisyieldedaFOS=1.03,showingasignificantincreaseduetothepresenceoftherootzonelocatedeverywhereonthegroundsurface.Theslopethatwasinitiallyunsafe(FOS=0.95)isnowmarginallysafe(FOS>1)duetotherootreinforcementeffects.ThedeformedmeshoftheslopeisshowninFigure4.Itisnotedthatthecriticalslipsurfaceisnolongerplanarbutiscircular.Figure4.DeformedMeshfortheSlopewithVegetationExtendingOvertheEntireGroundSurface(c′=0,cR=5kPa,hR=1m).Theaboveexampleshaveshownthatrootreinforcementcanimprovethestabilityofaslope.Byincorporatingtheapparentrootcohesionintherootzoneoftheslope,theFOSoftheslopeisincreased.Thecontributionofrootreinforcementtothestabilityofslopeissignificant.Referringtothe2:1homogenousslopeintheaboveexamples,thisslopewouldbeunstableiftheeffectofvegetationisnottakenintoaccount.Inreality,therearemanyslopesthatwouldfail,basedonthestabilityanalysisusingthefieldorlaboratorysoildata,butremainintactforalongperiodoftime.AcaseinpointistheThredbolandslide(Hand,2000).Thepresenceofvegetationonsuchslopesisclearlyoneofthemajorcontributionstothestabilityoftheseslopes.PARAMETRICSTUDIESParametricstudieswereperformedforarangeofthevegetationandsoilparameters.Theapparentrootcohesion(cR)wasvariedoverthefollowingrange:0≤cR≤20kPa(4) Threevaluesofdepthofrootzone(hR)wereused,namely:hR∈{1m,2m,3m}(5)Forthesoilproperties,onlytheeffectivecohesion(c′)wasvaried.Thevaluesofeffectivecohesion(c′)consideredwereasfollows:c′∈{1kPa,2kPa,3kPa,4kPa,5kPa}(6)TheresultsoftheparametricstudiesaresummarisedinFigure5to7.Figure5showsthevariationofthevaluesofFOSwiththeapparentrootcohesion(cR)wherec′=0andvegetationisconfinedtotheslopesurfaceonly.Twosetsofresultsarepresentedinthisfigure.Thebrokenlinesrepresenttheresultsforthecasewherevegetationisconfinedtotheslopesurfaceonly,withoutextendingtotheslopetoe.Thesolidlinesaretheresultsforthecasewheretheslopetoeelement(elementTinFigure3)isassumedtobeaffectedbyvegetation.Generally,thevaluesofFOSincreasewhenapparentrootcohesion(cR)increases.Forthecasewheretheslopetoeisnotprotectedbyvegetation,theFOSincreasesslightlyinitially,butdropstoalowervalueafterreachingamaximumvalueofFOS.TheFOSremainsconstantregardlessofanyincreaseintheapparentrootcohesion.Foracohesionlesssoilslope(c’=0),thefailuremechanismisashallowplanarfailure.Thisfailuremechanismispreventedwhenplantrootsarepresent.Astheapparentrootcohesionincreases,thecriticalslipsurfaceshiftsdeeperbelowthegroundsurface.Whenthecriticalslipsurfaceisbeyondtheextentoftherootzone,anyincreasesinapparentrootcohesiondonotleadtoanincreaseinFOSfortheslope.Sincetheslopetoeisnotprotectedbyvegetation,thisregionistheweakzone,andastheapparentrootcohesionintherootzoneincreases,failureisinitiatedfromthisregion.Thiseventuallytriggersfailureduetoadifferentmechanism–toefailure.Whentheslopetoeisprotectedbyvegetation,theFOSincreasesastheapparentrootcohesionincreases.Therefore,theslopetoeappearstobethemostcriticalregionwherevegetationneedstobeconsideredinslopestabilisation.Thus,inordertoensureimprovedstabilityofaslopeusingvegetation,therootzoneneedstoextendbeyondthetoeregion.Figure5.VariationofFOSfortheCasewhereVegetationisConfinedtotheSlopeSurfaceOnly(c′=0).Figure6showsthevariationofthevaluesofFOSwiththerootcohesion(cR)wherec′=0andvegetationextendsentirelyoverthegroundsurface,includingtheupperslope,slopesurfaceandslopetoe.TheFOSincreasesastheapparentrootcohesion(cR)increases.Itisnotedthat,whentheentireslopeisprotectedbyvegetation,theeffectsonFOSaresignificant.Forexample,whenhR=1mtheFOSisincreasedby26%forcR=20kPa.Theincreaseisevenmoresignificantwithadeeperrootzone(higherhR),asshowninFigure6.Figure6.VariationofFOSfortheCasewithVegetationExtendingOvertheEntireGroundSurface(c′=0).Figure7showsthevariationoftheFOSwiththedimensionlessparametercR/c′forthecasewheretheeffectivecohesionofthesoilc′∈{1kPa,2kPa,3kPa,4kPa,5kPa}.TheanalyseswereperformedforthecasewherevegetationextendseverywhereonthegroundsurfaceandhR=1m.TheanalysiswasterminatedatcR=20kPaforeachvalueofc′.ItisworthwhiletonotethattheincreaseintheFOSismoresignificantforaslopewithaloweffectivecohesion(c′=1kPa)comparedwithaslopewithahigheffectivecohesion(c′=5kPa).Examinationofthedeformedmeshesshowedthat,inthecaseofslopeswithhighervaluesofeffectivecohesion(c′),failureoccurredalongadeep-seatedrotationalslipsurface.Thisimpliesthatvegetationhaslessofaneffectondeep-seatedfailureswhenthedepthofrootzone(hR)isshallow.Figure7.VariationofFOSfortheCasewithVegetationExtendingOvertheEntireGroundSurface(c>0,hR=1m).FUTUREWORKByincorporatingtheeffectsofrootreinforcementinslopestabilityanalysis,significantinfluenceonthestabilityofslopeshasbeenobserved.Tomodelanaturalslopemoreaccurately,theinfluenceofsoilsuctionandsoilvariabilityshouldbetakenintoaccount.Thisworkwillbecarriedoutinthisongoingresearchproject,inparticular,toincorporatevariabilityofthevegetationandsoilpropertieswithinthefiniteelementframework.SUMMARYANDCONCLUSIONS Vegetationplaysanimportantroleinthestabilityofslopes.Rootreinforcementhasbeenconsideredasanincreaseinapparentsoilcohesion.Theapparentrootcohesion(cR)hasbeenincorporatedintheslopestabilityanalysisusingthefiniteelementmethod.Theextentofthevegetationeffectshasbeencharacterisedbythedepthofrootzone(hR).Thestabilityofaslopeissensitivetoboththeapparentrootcohesion(cR)anddepthofrootzone(hR).ThestabilityofslopesisimprovedwithanincreaseinthevaluesofcRandhR.Inaddition,resultsshowedthattheimprovementinFOSforaslopewithvegetationcoverovertheentiregroundsurfaceishighercomparedwithvegetationcoverontheslopesurfacealone.Thestudyhasalsoshownthattheeffectsofvegetationaremoresignificantinslopeswithlowvaluesofeffectivecohesionwhereshallowplanarfailuresarelikelytooccur.Correspondingly,vegetationhaslessofaneffectondeep-seatedfailure.植被模型對(duì)邊坡穩(wěn)定性的影響摘要：據(jù)了解，植被在兩個(gè)方面影響邊坡穩(wěn)定：水文效應(yīng)和機(jī)械效應(yīng)。水文效應(yīng)包括通過(guò)植被土壤水分蒸散，從而導(dǎo)致土壤吸力的增加或者孔隙水壓力的減少，因此，增加了土的抗剪強(qiáng)度。通過(guò)植物的根矩陣系統(tǒng)的力學(xué)效應(yīng)，也增加了土壤的抗剪強(qiáng)度。在土體內(nèi)根密度和根抗拉強(qiáng)度也有助于增加土壤的抵抗剪切能力。土壤吸力和根鋼筋的影響在表現(xiàn)土壤凝聚力方面已經(jīng)量化。本文利用有限元法分析植被在斜坡穩(wěn)定性方面的影響。兩個(gè)關(guān)鍵的植被參數(shù)已被納入有限元邊坡穩(wěn)定分析中，即明顯的根凝聚力（CR）和根區(qū)的深度（hR）。對(duì)由植被和土壤參數(shù)變化引起斜坡穩(wěn)定性的靈敏性進(jìn)行了參數(shù)研究評(píng)價(jià)，結(jié)果表明，植被在斜坡淺層失穩(wěn)中起著重要作用，并且顯著影響其穩(wěn)定性。引言邊坡失穩(wěn)災(zāi)害時(shí)巖土工程中的主要問(wèn)題之一，它的發(fā)生也會(huì)造成生命和財(cái)產(chǎn)的損失。這些失穩(wěn)的邊坡大多數(shù)是植被或森林覆蓋的天然斜坡。天然斜坡和與河堤或者人工斜坡是不同的，植被和土壤變異在它們的穩(wěn)定性方面起著重要作用。植被對(duì)斜坡穩(wěn)定性的影響是眾所周知的。植被通過(guò)改變土壤水分構(gòu)成的改變來(lái)影響斜坡的穩(wěn)定性，這反過(guò)來(lái)又導(dǎo)致土壤吸力或空隙壓力的變化。植被也可以通過(guò)根加固來(lái)提高斜坡的穩(wěn)定性。Wuetal.(1979)對(duì)移除植被前后斜坡的穩(wěn)定性進(jìn)行調(diào)查，得出結(jié)論，樹(shù)根提供的抗剪強(qiáng)度對(duì)斜坡的穩(wěn)定性是至關(guān)重要的。研究表明，植被可以通過(guò)根鋼筋提高坡體的抗剪強(qiáng)度。Wuetal.(1979)表示，如果在邊坡穩(wěn)定性分析中不考慮植被的影響，邊坡則可能發(fā)生失穩(wěn)。天然斜坡受制于土壤和植被固有的變異性。這就使得天然斜坡的底層土壤坡面不能完全一致或者同質(zhì)。即使是在一個(gè)相同土質(zhì)的土層，土壤的性質(zhì)從點(diǎn)到點(diǎn)也是變化的（Vanmarcke，1977年）。植被的生長(zhǎng)對(duì)環(huán)境狀況和變化非常敏感。通常不同類(lèi)型的植被生長(zhǎng)于一種天然的斜坡上，如牧草，藥材，灌木和樹(shù)木等。這些不同植物的大小和物理性的不同都會(huì)導(dǎo)致對(duì)斜坡穩(wěn)定有不同的影響。因此使用單一為分析植被參數(shù)的輸入值最好看作是原始條件下的近似值。本文利用有限元方法對(duì)植被影響斜坡穩(wěn)定性進(jìn)行調(diào)查。有限元法允許用戶將斜坡幾何分成小分子的方法來(lái)確定植被對(duì)斜坡穩(wěn)定性影響的程度。由于本文篇幅的限制，本文只將根鋼筋的影響納入邊坡穩(wěn)定分析，不考慮植被和土壤性質(zhì)的變化。2:1同質(zhì)坡（傾角26.57°角）用于研究植被對(duì)邊坡穩(wěn)定性的影響。兩個(gè)關(guān)鍵的植被參數(shù)被納入有限元邊坡穩(wěn)定性分析，即明顯的根凝聚力（CR）和根區(qū)的深度（hR）。同時(shí)對(duì)由植被和土壤參數(shù)變化引起斜坡穩(wěn)定性的靈敏性進(jìn)行了參數(shù)研究評(píng)價(jià)。植被對(duì)邊坡穩(wěn)定性影響的前期分析根筋模型在過(guò)去的三十年中，研究集中在利用植物根系加固穩(wěn)定斜坡。植物根系的能力來(lái)加強(qiáng)土壤穩(wěn)固是眾所周知的。有高抗拉強(qiáng)度的植物根系能利用其密集的根矩陣系統(tǒng)來(lái)提高土體的強(qiáng)度。土體質(zhì)量與植物根系是緊密聯(lián)系在一起的，土體抗剪強(qiáng)度就是利用這種影響增加的。根鋼筋對(duì)抗剪強(qiáng)度的貢獻(xiàn)被認(rèn)為是有凝聚力的特點(diǎn)Wuetal.(1979)。Wuetal.(1979)提出一個(gè)由于根加固土作用使土體抗剪強(qiáng)度增加的簡(jiǎn)化的量化模型。土體的抗剪強(qiáng)度的增加由以下關(guān)系表示：Sr=tR(cosθtanφ′+sinθ)(1)其中SR=由根鋼筋的加固引起的土體的剪切強(qiáng)度的增加值，tR=平均單位面積土壤根抗拉強(qiáng)度，θ=剪切旋轉(zhuǎn)的角度，φ'=摩擦角。由于植物根系的力學(xué)效應(yīng)可以提高土體的凝聚力，Sr，可視為相當(dāng)于土壤的凝聚力明顯，被稱(chēng)為表觀根凝聚力（CR）。表觀根凝聚力（CR）范圍典型值，從1kPa到17.5kPa（Coppin和Richards，1990）。這些值的獲得是根據(jù)幾個(gè)學(xué)者利用不同方法的研究，這些研究方法包括反分析、直接剪切試驗(yàn)、結(jié)合垂直根模型方程的根密度信息、結(jié)合根密度信息的反分析調(diào)查研究。表觀根凝聚力（CR）的值依賴(lài)于植被類(lèi)型和原始土壤條件的。前期邊坡穩(wěn)定性分析Wuetal.(1979)通過(guò)使用傳統(tǒng)的極限平衡法分析植被對(duì)邊坡穩(wěn)定性的影響。沿著潛在滑動(dòng)面的土壤抗剪強(qiáng)度極限平衡法，假設(shè)失穩(wěn)點(diǎn)得到充分調(diào)動(dòng)。用來(lái)描述土壤抗剪強(qiáng)度的Mohr-Coulomb方程：τ=c′+(σ-u)tanφ′(2)納入根鋼筋加強(qiáng)作用的影響，（2）式變?yōu)椋害?(c′+CR)+(σ-u)tanφ′(3)Wuetal.(1979)在他們的無(wú)限邊坡分析納入表觀根凝聚力（CR），并發(fā)現(xiàn)一些斜坡安全系數(shù)（FOS）有所增加。結(jié)果表明，樹(shù)根能改善有森林覆蓋的斜坡的穩(wěn)定性。現(xiàn)在還沒(méi)有發(fā)表的利用數(shù)值方程分析根加固效果的研究論文。本研究采用數(shù)值分析，允許限制根區(qū)的程度。通過(guò)對(duì)根區(qū)賦予不同的表觀根凝聚力（CR）值，評(píng)價(jià)其對(duì)斜坡安全系數(shù)（FOS）的重要意義。模型植被影響的數(shù)值研究的說(shuō)明在本研究中，采用有限元法已展開(kāi)對(duì)植被對(duì)斜坡穩(wěn)定性的影響的調(diào)查。有限元方法的離散化過(guò)程將邊坡幾何分解成多個(gè)小分子，這有利于在邊坡穩(wěn)定性中分析植被的影響。在邊坡穩(wěn)定性分析中植被的影響是通過(guò)修改個(gè)別土壤元素的性質(zhì)來(lái)發(fā)揮作用的。例如，在頂層的斜坡土壤元素可以有較高的凝聚力由于加上額外的根鋼筋的表觀根凝聚力（CR）值。植被造成土壤吸力的變化也可以納入有限元分析。定位植被影響因素的靈活性意味著可以有效地進(jìn)行建模的變量和隨機(jī)的自然植被的選取。本文主要是闡述有限的根鋼筋加強(qiáng)作用對(duì)斜坡穩(wěn)定性的影響。有限元模型在本研究中的有限元模型假定2維平面應(yīng)變條件。在這項(xiàng)研究中所使用的程序是由史密斯和格里菲斯（1998）提出的，它使用八面的四邊形單元，與莫爾-庫(kù)侖破壞準(zhǔn)則的彈塑性模型假設(shè)是一致的。這項(xiàng)計(jì)劃已被用來(lái)分析幾個(gè)邊坡穩(wěn)定性問(wèn)題，包括分層的影響和對(duì)邊坡和大壩穩(wěn)定的自由表面的影響（Griffiths和Lane，1999年）。程序計(jì)算使用的不收斂的解決方案，再加上作為指示故障情況（Griffiths和Lane，1999年）在節(jié)點(diǎn)位移突然增加（FOS）的斜坡安全的因素。在這項(xiàng)研究中，2:1同質(zhì)邊坡高度為10米（26.57°），用于研究植被對(duì)邊坡穩(wěn)定性的影響，如在圖1所示。土壤性質(zhì)如下：φ′=25°c′=0γ=20kN/m3兩個(gè)額外的植被在邊坡穩(wěn)定性分析中使用的參數(shù)是明顯的根凝聚力（CR）和根區(qū)的深度（hR）。明顯的根凝聚力（CR）是由植物的根矩陣系統(tǒng)造成的土壤表觀凝聚力。根區(qū)的深度（hR）定義為植物根系造成土的抗剪強(qiáng)度很少或根本沒(méi)有影響的有效距離之外?？紤]有兩種情況：（1）植被局限于坡面;（2）整個(gè)地面植被延長(zhǎng)。參數(shù)研究表明邊坡穩(wěn)定關(guān)鍵取決于對(duì)植被參數(shù)變化的敏感性。 圖1網(wǎng)為2:1均質(zhì)邊坡的邊坡角26.57°，φ=25°，C'=0結(jié)果分析邊坡沒(méi)有植被的影響（c′=0，CR=0）同時(shí)利用有限元法和極限平衡法對(duì)2:1均勻無(wú)植被邊坡穩(wěn)定性進(jìn)行了分析。極限平衡法使用GGU穩(wěn)定程序（巴斯，1999年）主教的簡(jiǎn)化方法進(jìn)行。分析結(jié)果列于表1。表1。使用不同的方法邊坡的安全系數(shù)。方法FOS有限元法0.95極限平衡法0.93這兩種方法提供了類(lèi)似的結(jié)果，盡管極限平衡法給的值比有限元法略小。圖2顯示了失穩(wěn)的的斜坡變形有限元網(wǎng)格，相應(yīng)的FOS=0.95。它可以觀察到失穩(wěn)的機(jī)制，是一灣淺淺的平面失穩(wěn)。問(wèn)題發(fā)生在第一層，延伸到2米以下的坡面。圖2C’=0邊坡失穩(wěn)的變形網(wǎng)格邊坡植被的影