Elastic Modulus of Soil

Document "Elastic Modulus of Soil" give you the knowledge: Effect of ocr and confining pressure on soil properties, youngs modulus of soil. Invite you to refer to the document content more learning materials and research.
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Elastic Modulus of SoilTableofContents 1. EFFECTOFOCRANDCONFININGPRESSUREON SOILPROPERTIESFollowinggivestheeffectofOCRonthestrengthparametersofthecohesivesoilandconfiningpressureonthenoncohesivesoil. 1.1 EffectofOCRonSoilStrengthParameter(cΦ SOIL) OCRofsoilisdefinedasthehigheststressexperiencedbythesoildividedbythecurrentstress.FollowingarethechartshowingtheeffectofOCRontheratioofthemaximumdeviatorstresstotheconfiningstress,angleofinternalfrictionandcohesionofthesoil(fig.1.1).1|PageInthepresentstudy,allsoilsamplesweretestedafterbeingsubjectedtodifferentinitialconsolidationpressure.Theinitialconsolidationpressures(σ0’)appliedtothesoilsamplewere50kPa,200kPaand400kPa.Itwasfoundthatwithincreaseofoverconsolidationratioincreases,themaximumdeviatorStress/σc’ratio(σc’=confiningpressure),angleofinternalfrictionandcohesionvalueincreases.Thiseffectisverifiedbytwoseparateexperiments.ExperimentswerecarriedonthenormallyconsolidatedsoilandOverconsolidatedsoil.PleasenotethatforNormallyconsolidatedsoilOCRvalueis1andforoverconsolidatedsoiltheOCR>1.Figure1.2representsTriaxialTestresultsonnormallyconsolidatedandoverconsolidatedsoil.2|Page fig1.2Failureenvelopefor(a)Normallyconsolidatedand(b)overconsolidatedclayfrom consolidateddrainedtriaxialtest.(DasB.M.,“AdvancedSoilMechanics”)ThevalueofcisobtainedbydrawingacommontangenttoMohr’scirclewhichisMohrcoulomb’senvelope.Infigure1.2(a),itisclearthatinnormallyconsolidatedclaythecohesioniszero.Butwhenoverconsolidatedclayasshowninfigure1.2(b)thefailureenvelopemakesaninterceptwiththeverticalgivingcohesionvalue.ThusastheOCRvalueincrease,theincreaseinthecohesionvalueisobserved. Fig1.3Failureenvelopeofsoilwithapreconsolidationpressureσc’. (DasB.M.,“AdvancedSoilMechanics”)3|PageThechangeintheangleofinternalfrictionisverifiedinthefollowingexperimentalobservation.Pleasereferfigure1.3.Ifasoilisinitiallyconsolidatedbyanencompassingchamberpressureofσc=σc’,andallowedtoswellunderreducedchamberpressureofσ3=σ3’,thespecimenwillbeoverconsolidated.Thefailureenvelopeobtainedfromtheconsolidateddrainedtriaxialtestsofthistypeofspecimenhastwodistinctbranches.Portion‘ab’oftheenvelopehasflatterslopewithacohesioninterceptandportion‘bc’representthenormallyconsolidatedsoilwithzerocohesion.ThusasthesoilturnsfromoverconsolidatedtonormallyconsolidatedortheOCRvaluedecreases,theangleofinternalfrictionofthesoilisincreasing.EffectofOCRontheElasticmodulusofsoil:Thefollowingcorrelationgivesrelationbetweenthesoilelasticmodulusandundrainedshearstrengthofsoil: Es=Kc.CuKc=correlationfactor(Figure1.4)Cu=undrainedshearstrength,tsf4|PageFig.1.4:CorrelationfactorbasedonOCR(www.geotechnicalinfo.com/youngs_modulus.html)5|Page 1.2 EffectofconfiningPressureonStressStrainBehaviour (CohesionlessSoil)Fig.1.5.StressRatio~AxialStrainandvolumetricStrain~Axialstrainrelationshipfromσh= constanttestsstartingfromisotropicStressState(ShearedAirdried;ε0=0.125%perminute) (Yasin,S.J.MandTatsuoka,F.,March16&17,2006“StressStrainBehaviourofaMicacious SandinplaneStraincondition”,GeotechnicalSymposiuminRoma)Figure1.5showstheeffectofinitialdensityandconfiningstressonthestressstrainbehaviorofsoilwhereσh’orσh=minorprincipalstressorconfiningpressure=constant’.Thestartingpoint6|Pageofeachcurvecorrespondtoisotropicstressstateofeither(σh)c=100KPaor(σh)c=400KPa.Thespecimenswereairdried.Thecontinuouslinesrepresentthecurveobtainedforthetestondensesandandthedottedforloosesand.Followingaretheobservation: 1. TestJ319Cwithdenseinitialstateandlowconfiningstressshowsharppeakin‘axial stress~axialstrain’relationandsamplealsostartsdilatingatpeakstresslevelandstillεvol ispositive(i.e.thevolumeislowerthantheinitialvolume). 2. OntheotherhandtestJ318Cwithdenseinitialstateandhighconfiningpressureshowed amoreductilebehaviorwithoutanysignofdilationevenatpeakstatethatresemblethe volumechangebehaviorofloosespecimens.Thusdensesandathighconfiningstressmaybehavelikealoosesandatlowconfiningstress.Figure1.6verifiestheobservation. Fig 1.6 Deviator Stress and Axial Strain confining Pressure of 50 kPa, 200 kPa and 400 kPaSivadass, T., Lee, C.Y. & Karim M.S.A, 2003, “ Behavior of a tropical residual soil”, ISBN 90 5809 6047|PageEffectofconfiningpressureontheElasticmodulusofsoil: Fig1.7Relationbetweentheinitialelasticmodulusandconfiningpressure (JuiPinWangandHoiI.Ling,Mohri,L.,16&17March2006,“StressStrainBehaviourOf CompactedSandClayMixture”,GeotechnicalSymposiuminRoma)Figure1.7showsthatElasticmodulusofunsaturatedspecimenathigherconfiningpressurehashigh elastic modulus. Generally the initial elastic modulus increased logarithmically withincreaseofconfiningpressure.8|Page 2. YOUNGSMODULUSOFSOIL2.1 IntroductionThemodulusofelasticityorY ...