非饱和土力学讲义(Fredlund在香港科大)chapter9ustmod.pdf

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1、Dr.A.WayneClifton•Therehasprobablybeenfarlessresearchdoneontheshearstrengthofunsaturatedsoilsthanonotherphysicalpropertiesandstillourunderstandingoftheshearstrengthofunsaturatedsoilshasmadeitpossibleforgeotechnicalengineerstosuccessfullyanalyzeslopestabilityandotherl

2、imitequilibriumanalysisproblems.1•Manygeotechnicalproblemssuchasbearingcapacity,lateralearthpressures,andslopestabilityrequireanassessmentoftheshearstrengthofthesoil.•Thischapterdescribeshowtheshearstrengthofanunsaturatedsoilcanbeformulatedintermsofstressstatevariabl

3、esandshearstrengthparameters.•Abriefhistoricalreviewofattemptstomeasurerelevantsoilpropertiesisgivenpriortoformulatingtheshearstrengthequation.•Thetheoryassociatedwithvarioustypesoftriaxialtestsanddirectsheartestsforunsaturatedsoilsarecomparedanddiscussed.•Theshearst

4、rengthequationforanunsaturatedsoilispresented,bothinmathematicalandgraphicalforms.•Thepossibilityofnon-linearityintheshearfailureenvelopeisdiscussedandvariousmethodsforhandlingthenon-linearityareoutlined.Additionalnotes:2•Theshearstrengthofasaturatedsoilismostcommonl

5、ydescribedusingtheMohr-Coulombfailurecriterionandtheeffectivestressstatevariable(Terzaghi,1936).•Thisequationdefinesastraightlineandisreferredtoasthefailureenvelope.•Thisenveloperepresentspossiblecombinationsofshearstrengthandeffectivenormalstressonthefailureplane(at

6、failure).•Theshearstrengthandnormalstressaregiventhesubscript“f”,whichreferstothefailureplane(i.e.,the“f”subscriptinsidethebrackets)andtothefailurestressconditions(i.e.,the“f”subscriptoutsidethebrackets).•Pore-waterpressureactsequallyonallplanes(i.e.,isotropic).•Thes

7、hearstressdescribedbythefailureenvelopeindicatestheshearstrengthofthesoilforeacheffectivenormalstress.•ThefailureenvelopeisobtainedbyplottingalinetangenttoaseriesofMohrcirclesrepresentingfailureconditions.Additionalnotes:3•Thedefinitionofshearstrengthinsoilmechanicsp

8、racticeisbasedonstressversusstraincurves.•Totalvolumechangeandwatervolumechangearethedeformationvariablesthatarenecessarytothecompl