[靜止土壓力]

1、Chapter6LateralEarthPressure(Part1)6.1EarthPressureatrest[靜止土壓力靜止土壓力](Ko)(i)ConsiderthewallshowninFigure6.1.Assumethereisnogroundwatertable.Ifnomovementofthewalltakesplacethesoilisatrest.(ii)Thelateralearthpressureatrest

2、[靜止土壓力](eo)actingonasoilelementlocatedatadepthofzis:(6.1)zKeoo????whereKoiscoefficientofearthpressureatrest[靜止土壓力系數(shù)]?isunitweightofsoil.Koistheratioofhizontalverticaleffectivestresseswhenaretainingwalldoesnotmoveatall“at

3、rest”.(iii)Jaky(1944)proposedthefollowingempiricalexpressiontoestimateKofnmallyconsolidatedsoil[正常固結(jié)土]:(6.2)sin1Ko???where?’iseffectiveangleofinternalfriction[有效內(nèi)摩擦角].(iv)Thelateralearthpressurevarieslinearlywithdepth.Th

4、etotallateralfceperunitlength(Eo)imposedonaretainingwallis:(6.3)2ooHK21E????whereHisheightofthewallEoisactingatH3fromthebottomofthewall.6.2Rankine’sEarthPressureThey[朗肯土壓力理論朗肯土壓力理論]Thefollowingassumptionsaremadetodevelop

5、theRankine’searthpressurethey:(i)Thewallisrigidverticalfrictionlessextendstoaninfinitedepth(ii)Thebackfillisadryhomogeneousisotropiccohesionlesssoilmass(iii)Thesoilsurfaceishizontaltherearenoshearstressesonhizontalvertic

6、alplanesi.e.thehizontalverticalstressesareprincipalstresses.6.2.1ActiveEarthPressure[主動(dòng)土壓力](i)Ifthewallismovedawayfromthebackfill(ABtoA’BinFigure6.2)theeffectivehizontalstresswillreducebuttheeffectiveverticalstresswillre

7、mainconstant.(ii)TherefetheMohr’scirclewillexpasshowninFigure6.3untiltouchingtheMohrCoulombfailuresurfacethesoilelementswillundergoactivefailure[主動(dòng)破壞].(iii)Theslipplanesfactivefailureareinclinedat45?’2withrespecttothehiz

8、ontal.The(iii)Onlyasmallmovementofthewallawayfromthesoilisrequiredtomobilisefullactiveearthpressureinthesoilmass(seeFigure6.8).(iv)Substantialwallmovementtowardsthesoilisrequiredtomobilisefullpassiveearthpressureinthesoi

9、lmass.(v)Rankine’searthpressurecoefficientsareonlyapplicabletoafrictionlessrigidverticalwallretaininghomogeneoussoilwithahizontalgroundsurface.6.2.4Effectofgroundwatertableonearthpressure(i)Ifgroundwaterispresentthepewat

10、erpressuremustbeaddedtothelateralearthpressure.(ii)DONOTmultiplythepewaterpressurewithacoefficientofearthpressure.(iii)IfthegroundwatertableislocatedataheightH2fromthebottomofthewall(seeFigure6.9)thehydrostaticpewaterpre

11、ssureis?wH2thetotalimposedlateralfceduetogroundwateris?wHw2(iv)Belowgroundwatertablethesubmergedunitweight(?’)isusedtoevaluatetheearthpressure.6.2.5Backfilliscohesivesoil(i)Ifthebackfilloftheretainingwallisacohesivesoilt

12、hecohesion(c)isnotzero.(ii)Atadepthzfromthetopofthewall(seeFigure6.10)theactive(ea)passive(ep)earthpressureareasfollows:(6.10)aaaKc2zKe??????(6.11)pppKc2zKe??????(6.12)aoKc2z???KeywdsAdhesion粘著力Backfill回填土Coefficientofea

13、rthpressure土壓力系數(shù)Coefficientofactiveearthpressure主動(dòng)土壓力系數(shù)Coefficientofearthpressureatrest靜止土壓力系數(shù)Coefficientofpassiveearthpressure被動(dòng)土壓力系數(shù)Cohesion粘聚力Cohesionlesssoils無粘性土Cohesivesoils粘性土CulmannConstruction(庫爾曼圖解法)Earthpressu