学位论文外文 翻译.docx
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学位论文外文 翻译.docx
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学位论文外文翻译
Section3Designphilosophy,designmethodandearthpressures
3.1Designphilosophy
3.1.1General
Thedesignofearthretainingstructuresrequiresconsiderationoftheinteractionbetweenthegroundandthestructure.Itrequirestheperformanceoftwosetsofcalculations:
1)asetofequilibriumcalculationstodeterminetheoverallproportionsandthegeometryofthestructurenecessarytoachieveequilibriumundertherelevantearthpressuresandforces;
2)structuraldesigncalculationstodeterminethesizeandpropertiesofthestructuralsectionsnecessarytoresistthebendingmomentsandshearforcesdeterminedfromtheequilibriumcalculations.
Bothsetsofcalculationsarecarriedoutforspecificdesignsituations(see3.2.2)inaccordancewiththeprinciplesoflimitstatedesign.Theselecteddesignsituationsshouldbesufficiently
Severeandvariedsoastoencompassallreasonableconditionswhichcanbeforeseenduringtheperiodofconstructionandthelifeoftheretainingwall.
3.1.2Limitstatedesign
Thiscodeofpracticeadoptsthephilosophyoflimitstatedesign.Thisphilosophydoesnotimposeuponthedesigneranyspecialrequirementsastothemannerinwhichthesafetyandstabilityoftheretainingwallmaybeachieved,whetherbyoverallfactorsofsafety,orpartialfactorsofsafety,orbyothermeasures.Limitstates(see1.3.13)areclassifiedinto:
a)ultimatelimitstates(see3.1.3);
b)serviceabilitylimitstates(see3.1.4).
Typicalultimatelimitstatesaredepictedinfigure3.Rupturestateswhicharereachedbeforecollapseoccursare,forsimplicity,alsoclassifiedandtreatedasultimatelimitstates.Ultimatelimitstatesinclude:
a)instabilityofthestructureoranyhartofit,includingsupportsandfoundations,consideredasarigidbody;
b)failurebyruptureofthestructureoranypartofit,includingsupportsandfoundations.
3.1.3Ultimatelimitstates
3.1.3.1General
Thefollowingultimatelimitstatesshouldbeconsidered.Failureofaretainingwallasaresultof:
a)instabilityoftheearthmass,e.g.aslipfailure,overturningorarotationalfailurewherethedisturbingmomentsonthestructureexceedtherestoringmoments,atranslationalfailurewherethedisturbingforces(see1.3.8)exceedtherestoringforcesandabearingfailure.Instabilityoftheearthmassaim-involvingaslipfailure,mayoccurwhere:
1)thewallisbuiltonslopinggroundwhichitselfisclosetolimitingequilibrium;or
2)thestructureisunderlainbyasignificantdepthofclaywhoseundrainedstrengthincreasesonlygraduallywithdepth;or
3)thestructureisfoundedonarelativelystrongstratumunderlainbyweakerstrata;or
4)thestructureisunderlainbystratawithinwhichhighporewaterpressuresmaydevelopfromnaturalorartificialsources.
b)failureofstructuralmembersincludingthewallitselfinbendingorshear;
c)excessivedeformationofthewallorgroundsuchthatadjacentstructuresorservicesreachtheirultimatelimitstate.
3.1.3.2analysismethod
Wherethemodeoffailureinvolvesaslipfailurethemethodsofanalysis,forstabilityofslopes,aredescribedinBS6031andinBS8081.Wherethemodeoffailureinvolvesabearingcapacityfailure,thecalculationsshouldestablishaneffectivewidthoffoundation.Thebearingpressuresasdeterminedfrom4.2.2shouldnotexceedtheultimatebearingcapacityinaccordancewithBS8004.
Wherethemodeoffailureisbytranslationalmovement,withpassiveresistanceexcluded,stableequilibriumshouldbeachievedusingthedesignshearstrengthofthesoilincontactwiththebaseoftheearthretainingstructure.
Wherethemodeoffailureinvolvesarotationalortranslationalmovement,thestableequilibriumoftheearthretainingstructuredependsonthemobilizationofshearstresseswithinthesoil.Thefullmobilizationofthesoilshearstrengthgivesrisetolimitingactiveandpassivethrusts.Theselimitingthrustsactinconcertonthestructureonlyatthepointofcollapse,i.e.ultimatelimitstate.
3.1.4Serviceabilitylimitstates
Thefollowingserviceabilitylimitstatesshouldbeconsidered:
a)substantialdeformationofthestructure;
b)substantialmovementoftheground.
Thesoildeformations,whichaccompanythefullmobilizationofshearstrengthinthesurroundingsoil,arelargeincomparisonwiththenormallyacceptablestrainsinservice.Accordingly,formostearthretainingstructurestheserviceabilitylimitstateofdisplacementwillbethegoverningcriterionforasatisfactoryequilibriumandnottheultimatelimitstateofoverallstability.However,althoughitisgenerallyimpossibleorimpracticaltocalculatedisplacementsdirectly,serviceabilitycanbesufficientlyassuredbylimitingtheproportionofavailablestrengthactuallymobilizedinservice;bythemethodgivenin3.2.4and3.2.5.
Thedesignearthpressuresusedforserviceabilitylimitstatecalculationswilldifferfromthoseusedforultimatelimitstatecalculationsonlywherestructuresaretobesubjectedtodifferingdesignvaluesofexternalloads(generallysurchargeandliveloads)fortheultimatelimitstateandfortheserviceabilitylimitstate.
3.1.5Limitstatesandcompatibilityofdeformations
Thedeformationofanearthretainingstructureisimportantbecauseithasadirecteffectupontheforcesonthestructure,theforcesfromtheretainedsoilandtheforceswhichresultwhenthestructuremovesagainstthesoil.Thestructuralforcesandbendingmomentsduetoearthpressuresreduceasdeformationofthestructureincreases.
Themaximumearthpressuresonaretainingstructureoccurduringworkingconditionsandthenecessaryequilibriumcalculations(see3.2.1)arebasedontheassumptionthatearthpressuresgreaterthanfullyactivepressure(see1.3.11)andlessthanfullypassivewillactontheretainingstructureduringservice.Asultimatelimitstatewithrespecttosoilpressuresisapproached,withsufficientdeformationofthestructure,theactiveearthpressure(see1.3.1)intheretainedsoilreducestothefullyactivepressureandthepassiveresistance(see1.3.15)tendstoincreasetothefullavailablepassiveresistance(see1.3.12).
Thecompatibilityofdeformationofthestructureandthecorrespondingearthpressuresisimportantwheretheformofstructure,forexampleaproppedcantileverwall,preventstheoccurrenceoffullyactivepressureattheprop.Itisalso
particularlyimportantwherethestructurebehavesasabrittlematerialandlosesstrengthasdeformationincreases,suchasanunreinforcedmassgravitystructureorwherethesoilisliabletostrainsofteningasdeformationincreases.
3.1.6Designvaluesofparameters
Theseareapplicableatthespecifiedlimitstatesinthespecifieddesignsituations.Allelementsofsafetyanduncertaintyshouldbeincorporatedintothedesignvalues.
Theselectionofdesignvaluesforsoilparameters
shouldtakeaccountof:
a)thepossibilityofunfavorablevariationsinthevaluesoftheparameters;
b)theindependenceorinterdependenceofthevariousparametersinvolvedinthecalculation;
c)thequalityofworkmanshipandlevelofcontrolspecifiedfortheconstruction.
3.1.7Appliedloads
Thedesignvalueforthedensityoffillmaterials,shouldbeapessimisticorunfavorableassessmentofactualdensity.
Forsurchargesandliveloadingsdifferentvaluesmaybeappropriateforthedifferingconditionsofserviceabilityandultimatelimitstatesandfordifferentloadcombinations.Theintentionofthiscodeofpracticeistodeterminethoseearth
pressureswhichwillnotbeexceededinalimitstate,ifexternalloadsarecorrectlypredicted.Externalloads,suchasstructuraldeadloadsorvehiclesurchargeloadsmaybespecifiedinothercodesasnominalorcharacteristicvalues.Someofthestructuralcodes,withwhichthiscodeinterfaces,specifydifferentloadfactorstobeappliedforserviceabilityorultimatelimitstatethechecksandfordifferentloadcombinations,
See3.2.7.Designvaluesofloads,derivedbyfactoringorotherwise,areintended,here,tobe
heremostpessimisticorunfavorableloadswhichshouldheusedinthecalculationsforthestructure.Similarly,whenexternalloadsactontheactiveorretainedsideofthewallthesesameexternalloadsshouldbederivedinthesameway.Thesoilisthentreatedasformingpartofthewholestructuralsystem.
3.1.8Designsoilstrength(see1.3.4)
Assessmentofthedesignvaluesdependsontherequiredoranticipatedlifeofthestructure,butaccountshouldbetakenalsooftheshort-termconditionswhichapplyduringandimmediatelyfollowingtheperiodofconstruction.Singledesignvaluesofsoilstrengthshouldbeobtainedfromaconsiderationoftherepresentativevaluesforpeakandultimatestrength.Thevaluesoselectedwillsatisfy,simultaneously,theconsiderationsofultimateandserviceabilitylimitstates.Thedesignvalueshouldbethelowerof:
a)thatvalueofsoilstrength,onthestress-strainrelationleadingtopeakstrength,whichismobilizedatsoilstrainsacceptableforserviceability.ThiscanbeexpressedasthepeakstrengthreducedbyamobilizationfactorMasgivenin3.2.4or3.2.5;or
b)thatvaluewhichwouldbemobilizedatcollapse,aftersignificantgroundmovements.Thiscangeneralbetakent.obethecriticalstatestrength.
Designvaluesselectedinthiswayshouldbecheckedtoensurethattheyconformto3.1.6.Designvaluesshouldnotexceedrepresentativevaluesofthefullysoftenedcriticalstatesoilstrength.
3.1.9Designearthpressures
Thedesignvaluesoflateralearthpressureareintendedtogiveanoverestimateoftheearthpressureontheactiveorretained
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