[静止土压力]

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1、Chapter6LateralEarthPressure(Part1)6.1EarthPressureatrest[静止土压力](Ko)(i)ConsiderthewallshowninFigure6.1.Assumethereisnogroundwatertable.Ifnomovementofthewalltakesplace,thesoilisatrest.(ii)Thelateralearthpressureat-rest[静止土压力](eo)actingonasoilelementlo

2、catedatadepthofzis:(6.1)whereKoiscoefficientofearthpressureat-rest[静止土压力系数]andgisunitweightofsoil.Koistheratioofhorizontalandverticaleffectivestresseswhenaretainingwalldoesnotmoveatallor“atrest”.(iii)Jaky(1944)proposedthefollowingempiricalexpressiont

3、oestimateKofornormallyconsolidatedsoil[正常固结土]:(6.2)wheref’iseffectiveangleofinternalfriction[有效內摩擦角].(iv)Thelateralearthpressurevarieslinearlywithdepth.Thetotallateralforceperunitlength(Eo)imposedonaretainingwallis:(6.3)whereHisheightofthewallandEois

4、actingatH/3fromthebottomofthewall.6.2Rankine’sEarthPressureTheory[朗肯土压力理论]ThefollowingassumptionsaremadetodeveloptheRankine’searthpressuretheory:(i)Thewallisrigid,vertical,frictionlessandextendstoaninfinitedepth(ii)Thebackfillisadry,homogeneous,isotr

5、opicandcohesionlesssoilmass(iii)Thesoilsurfaceishorizontalandtherearenoshearstressesonhorizontalandverticalplanes,i.e.thehorizontalandverticalstressesareprincipalstresses.6.2.1ActiveEarthPressure[主动土压力](i)Ifthewallismovedawayfromthebackfill(ABtoA’Bin

6、Figure6.2),theeffectivehorizontalstresswillreducebuttheeffectiveverticalstresswillremainconstant.(ii)Therefore,theMohr’scirclewillexpandasshowninFigure6.3untiltouchingtheMohr-Coulombfailuresurfaceandthesoilelementswillundergoactivefailure[主动破坏].(iii)

7、Theslipplanesforactivefailureareinclinedat45°+f’/2withrespecttothehorizontal.(iii)Theactiveearthpressure[主动土压力](ea)actingonasoilelementlocatedatadepthofzis:(6.4)whereKaiscoefficientofactiveearthpressure[主动土压力系数]andgisunitweightofsoil.Kaistheratioofho

8、rizontalandverticaleffectivestresseswhenaretainingwallmovesaway(byasmallamount)fromtheretainedsoilandisdefinedbythefollowingexpression:(6.5)(v)Theactiveearthpressurevarieslinearlywithdepth(seeFigure6.4).Thetotallateralforceperunitlength(Ea)imposedona