CSSMforDummies临界状态土力学的讲座

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1、2006Critical-StateSoilMechanicsForDummiesPaulW.Mayne,PhD,P.E.Civil&EnvironmentalEngineeringGeorgiaInstituteofTechnologyAtlanta,GA30332-0355www.ce.gatech.eduEmail:paul.mayne@ce.gatech.eduPROLOGUECritical-statesoilmechanicsisaneffectivestressframeworkdescribingmechanicalsoilresponseI

2、nitssimplestformhere,weconsideronlyshear-inducedloading.Wemerelytietogethertwowell-knownconcepts:(1)one-dimensionalconsolidationbehavior,representedbye-logsv’curves;and(2)shearstress-vs.normalstress(t-sv’)fromdirectshearboxorsimpleshearing.Herein,onlythebareessenceofCSSMconceptsarepr

3、esented,sufficienttodescribestrength&compressibilityresponse.CriticalStateSoilMechanics(CSSM)ExperimentalevidenceprovidedbyHvorslev(1936;1960,ASCE);Henkel(1960,ASCEBoulder)Henkel&Sowa(1961,ASTMSTP361)Mathematicspresentedelsewhere,including:Schofield&Wroth(1968);Burland(1968);Wood(199

4、0).Inbasicform:3materialconstants(f',Cc,Cs)plusinitialstate(e0,svo',OCR)ConstitutiveModels,include:OriginalCam-Clay,ModifiedCamClay,NorSand,BoundingSurface,MIT-E3(Whittle,1993)&MIT-S1(Pestana)andothers(Adachi,Oka,Ohta,Dafalias)"Undrained"isjustonespecificstresspathYet!!!CSSMismissing

5、frommosttextbooksandundergrad&gradcurriculaintheUSA.One-DimensionalConsolidationCc=0.38Cr=0.04svo'=300kPasp'=900kPaOverconsolidationRatio,OCR=3Cs=swellingindex(=Cr)cv=coef.ofconsolidationD'=constrainedmodulusCae=coef.secondarycompressionk≈hydraulicconductivitysv’DirectShearTestResult

6、ssv’tDirectShearBox(DSB)sv’tDirectSimpleShear(DSS)tdtgsCSSMforDummiesLogsv'Effectivestresssv'ShearstresstVoidRatio,eNCCCtanf'CSLEffectivestresssv'VoidRatio,eNCCSLCSSMPremise:“Allstresspathsfailonthecriticalstateline(CSL)”CSLfc=0CSSMforDummiesLogsv'Effectivestresssv'ShearstresstVoid

7、Ratio,eVoidRatio,eNCNCCCtanf'CSLCSLCSLSTRESSPATHNo.1NCDrainedSoilGiven:e0,svo’,NC(OCR=1)e0svosvoDrainedPath:Du=0tmax=c+stanfefDeVolumeChangeisContractive:evol=De/(1+e0)<0Effectivestresssv'c’=0CSSMforDummiesLogsv'Effectivestresssv'ShearstresstVoidRatio,eVoidRatio,eNCNCCCtanf'CSLC

8、SLCSLSTRESSP