深基坑開挖與支護設計

TheDepartmentofCivil&StructuralEngineeringTheHongKongPolytechnicUniversity,HongKong,China1OutlineofLecturesbyJHYIN:Lecture1:SubsoilExploration(Chapter2-Das)Lecture2: ShallowFoundations(Chapter3-Das)Lecture3: MatFoundations(Chapter4-Das)Lecture4: LateralEarthPressureandRetainingWalls(Chapter5-Das)Lecture5: SheetPileWalls(Chapter6-Das)Lecture6: BracedCuts(Chapter7-Das)Lecture7: PileFoundations(Chapter8-Das)Lecture8: SoilImprovementandGroundModification(Chapter11-Dasplusothers)EssentialReferences:Das,BrajaM.(2007).PrinciplesofFoundationEngineering(6thedition),Thomson,UnitedStates(ISBN0-534-40752-8)26.1Introduction6.2ConstructionMethods(施工方法)6.3CantileverSheetPileWalls（懸臂板樁墻）6.4CantileverSheetPilingPenetratingSandySoils6.5CantileverSheetPilingPenetratingClay6.6AnchoredSheetWalls6.7FreeEarthSupportMethodforPenetrationofSandySoil6.8MomentReductionforAnchoredSheetPileWalls6.9FreeEarthSupportMethodforPenetrationofClayLecture6:SheetPileWalls(Chapter6-Das)板樁墻36.10Anchors6.11UltimateResistanceofAnchorPlatesandBeamsinSand（錨板和錨梁的極限承載力）6.12UltimateResistanceofAnchorPlatesandBeamsinClay(fu=0condition)6.13FactorSafetyforAnchorPlatesandBeamsLecture6:SheetPileWalls(Chapter6-Das)板樁墻46.1IntroductionPurposes:

supportingexcavation,retainingsoil,stoppingwaterinflow,…支撐開挖，擋土，阻止水滲流5Diaphragmwallsareundergroundstructuralelementscommonlyusedforretentionsystems,permanentfoundationwalls,deepgroundwaterbarriers.地下連續墻普遍用于支撐體系，永久性的基礎外墻，擋水的地下結構體。Diaphragmwallsareconstructedusingtheslurrytrenchtechnique,whichwasdevelopedinEuropeandhasbeenusedinHongKongsincethe1970‘s.地下連續墻施工過程中采用了泥漿護壁。Thetechniqueinvolvesexcavatinganarrowtrenchthatiskeptfullofanengineeredfluidorslurry.泥漿護壁技術是開挖窄槽..Theslurryexertshydraulicpressureagainstthetrenchwallsandactsasshoringtopreventcollapse.泥漿給窄槽壁施加水壓，防止坍塌

Slurrytrenchexcavationscanbeconstructedinalltypesofsoil,evenbelowthegroundwatertable.泥漿護壁溝渠開挖適用于各種土層Diaphragmwalls（地下連續墻）:6BentoniteSlurry（工程中配置泥漿的原理圖）73-DViewofDiaphragmWallConstruction89Woodensheetpileandconcretesheetpile（木板樁，混凝土板樁）:10Steelsheetpile(usedalotinHongKong):11SteelsheetpilesfromJapanandUKareoftenusedinHongKong.

BelowisfromUSA.12136.2ConstructionMethods(后填土支護的施工過程)14156.3CantileverSheetPileWalls（懸臂板樁墻，實際變形、受力圖）Rotationpoint:Howtofindit?旋轉點？16FromSoilMechanicsbyCraig(2004)(7thEdition)兩種力學模型Fixedearth(bendinghere)Freeearth(nobendinghere)(simpleandgood)176.4CantileverSheetPilingPenetratingSandySoilsFixedearthmethod(bendinghere)18Purpose:TodesignD（入土深度）forthesheetpiletobesafe!Seeequationsbelow:Nowaterpressureisconsidered:self-balanced（自平衡）1920212223獲得壓力圖形的步驟24最大彎矩的計算剪力為0點252627282930316.5CantileverSheetPilingPenetratingClayL3=D-L4TwoequationsforDandL4Fixedearthmethod(bendinghere)3233L3=D-L4TwoequationsforDandL43435363738394041Freeearthmethod(nobendingat“O”)(simpleandgood):fromSoilMechanicsbyCraig(2004)42Watertablesinfrontandbackofthesheetpileisthesame.Thereisnoseepage.Thewaterpressureisself-balanced.2.25m0.225m>0.25mDepthd=2.75m6.25m7m6.625m4344FromTable5.6(a)withd=2.75andhorizontalforceequilibriumWhy6.625m?45Freeearthmethod:morefromDrYMChengR=?andcheckingD46R=?andNOcheckingDH47水頭差滲流路徑水力梯度48R=?andNOchecking試算時，可取D=h4950516.6AnchoredSheetWallsFreeFixedbyearthTwomethods:Freeearthsupport(simpleandgood)Fixedearthsupport(complicatedandmoreaccurate)Dfreeearth<Dfixedearth52536.7FreeEarthSupportMethodforPenetrationofSandySoil(c’=0)

Arevisedapproachcanbeusedforcohesivesoilwithc’andf’–how?54555657

Revisedapproachcanbeusedforcohesivesoilwithc’andf’–how?58Freeearthmethod:fromSoilMechanicsbyCraig(2004)59Twoequations(momentatAandhorizontalforceequilibriums)fortwounknowns(dandT)60616263ConsideringeffectivestressincreaseduetoseepageConsideringeffectivestressdecreaseduetoseepageThisisatrialanderrormethod64Seetherightfigure,forFr=2.0,dis6.3mForlimitcaseofFr=1.0,dis4.2m65Thisisonsafeside.6667Themaximumbendingmomentandshearforcecanbefoundfordesignpurpose.68Freeearthmethod:morefromDrYMChengDredgelinex69Noconsiderationontheeffectivestressincrease/decreaseduetoseepage;butokasasimpleapproach70716.8MomentReductionforAnchoredSheetPileWallsWhyreduction?Mmaxfromthepreviousmethod(freeearthmethod)maybereducedsincesheetpilesareflexible,leadingtoredistributionofearthpressures.Howtomakecorrectionforthereduction?Notcoveredinthissubject!

72737475766.9FreeEarthSupportMethodforPen