土木工程专业英语 课件 9.1 9.2 Chapter 9 Soil Mechanics and Foundation Engineering

Chapter9SoilMechanicsandFoundationEngineering9.1LateralEarthPressureCantileverretainingwallBracedexcavation

AnchoredsheetpileGravityRetainingwall

SoilnailingReinforcedearthwall

Thedesignoftheretainingstructurerequiresthedeterminationofthemagnitudeandlineofactionofthelateralearthpressure.Themagnitudeofthelateralearthpressuredependsuponanumberoffactors,suchasthemodeofmovementofthewall,theflexibilityofthewall,thepropertiesofthesoil,andthedrainageconditions.Forconvenience,theretainingwallisassumedtoberigidandthesoilstructureinteractioneffectisneglectedwhicharisesduetotheflexibilityofthewall.9.1.1CategoriesofLateralEarthPressureatrestearthpressure(静止土压力)activeearthpressure(主动土压力)passiveearthpressure(被动土压力)Wallmovementforthedevelopmentofactiveandpassiveearth

ActiveEarthPressure

PassiveEarthPressure

9.1.2Atrestearthpressurecoefficient=constant=

Lateralearthpressureforatrestcondition

ActiveandPassiveEarthPressureCoefficientsTheRankineTheoryActive:Passive:

TheCoulombactiveandpassiveearthpressurecoefficient

9.1.3CalculatingtheVerticalEffectiveOverburdenPressureWhereγisthetotalunitweightofthesoilandγ’istheeffective(orsubmerged)unitweightofthesoilwhichequalsthetotalunitweightofsoilminustheunitweightofwater.

9.1.4CalculatingtheLateralEarthPressureActivelateralearthpressure

Passivelateralearthpressure

9.1.5CalculatingtheTotalLateralEarthPressureForceThetotalactiveearthpressureforce:Thetotalpassiveearthpressureforce:Thetotalforceactsalongthebackofthewallataheightoffromthebaseofthewall.9.1.6OtherForcesActingontheWall

SurchargeLoad

EarthquakeForceWaterPressure

CompactionWhatarethefactorsinfluencingthemagnitudeofthelateralearthpressure?Namethethreecategoriesoflateralearthpressure.Howwouldyoucalculatetheverticaleffectiveoverburdenpressure?Whatistherelationshipbetweentheverticaleffectiveoverburdenpressureandthelateralearthpressure?Nametheforceactingonaretainingwall.

Questions9.2Footings

9.2.1IntroductionFootingsarestructuralmembersusedtosupportcolumnsandwallsandtotransmitanddistributetheirloadstothesoil.Theamountofsettlementdependsonmanyfactors,suchasthetypeofsoil,theloadintensity,thedepthbelowgroundlevel,andthetypeoffooting.9.2.2TypesofFootings

9.2.3DesignConsideration

Theareaofthefoundationbasedonallowablebearingcapacity(2)Twowayshearorpunchingshear(3)One-wayshear(4)Bendingmomentandsteelreinforcementrequired(5)Dowelrequirements(6)Developmentlengthofbars(7)DifferentialsettlementSizeofFootings

FlexuralReinforcementandFootingReinforcementDowelsonFootingsDowelsarerequiredinanycase,evenifthebearingstrengthisadequate.Theminimumnumberofdowelbarsneededisfour;thesemaybeplacedatthefourcornersofthecolumn.Thedowelbarsareusuallyextendedintothefooting,bentattheirends,andtiedtothemainfootingreinforcement.Dowelsshouldextendintothefootingadistancenotlessthanthedevelopmentlengthofthedowels.DifferentialSettlement

Theamountofdifferentialsettlementdependsonthevariationinthecompressibilityofthesoils,thethicknessofcompressiblematerialbelowfoundationlevel,andthestiffnessofthecombinedfootingandsuperstructure.Forpracticalpurposes,itcanbeassumedthatthesoilpressureundertheeffectofsustainedloadingsisthesameforallfootings,thuscausingequalsettlements.Single-ColumnSpreadFootings

Therequiredbearingareaisobtainedbydividingthetotalload,includingtheweightofthefooting,bytheselectedbearingpressure.Weightsoffootings,atthisstage,mustbeestimatedandusuallyamountto4to8%ofthecolumnload,theformervalueapplyingtothestrongertypesofsoils.Insinglefootings,theeffectivedepthismostlygovernedbyshear.Twodifferenttypesofshearstrengtharedistinguishedinsinglefootings:two-way(orpunching)shearandone-way(orbeam)shear.9.2.4CombinedFootings

Inbuildingswheretheallowablesoilpressureislargeenoughforsinglefootingstobeadequateformostcolumns,two-columnfootingsareseentobecomenecessaryintwosituations:(1)ifcolumnsaresoclosetothepropertylinethatsingle-columnfootingscannotbemadewithoutprojectingbeyondthatline,and(2)ifsomeadjacentcolumnsaresoclosetoeachotherthattheirfootingswouldmerge.9.2.5

Strip,Grid,andMatFoundationsGridfoundationMatfoundation(交叉条形基础)(筏板基础)MatfoundationStripfooting(条形基础)Inthecaseofheavilyloadedcolumns,particularlyiftheyaretobesupportedonrelativelyweakorunevensoils,continuousfoundationsmaybenecessary.9.2.6FootingsonPiles(桩基础)Ifthebearingcapacityoftheuppersoillayersisinsufficientforaspreadfoundation,butfirmerstrataareavailableatgreaterdepth,pilesareusedtotransfertheloadstothesedeeperstrata.Whatarethefunctionsoffooting?Whatarethefactor