基礎(chǔ)工程英文復(fù)習(xí)課件

第一章3/14/20231基礎(chǔ)工程基礎(chǔ)工程研究下部結(jié)構(gòu)物與巖土相互作用共同承擔(dān)上部結(jié)構(gòu)物所產(chǎn)生各種強(qiáng)度、變形與穩(wěn)定問題。樁、墩基、箱基、支擋結(jié)構(gòu)、圍護(hù)結(jié)構(gòu)、水泥攪拌體，砂石樁體，錨固，土釘、砂井等等，都可視為結(jié)構(gòu)物與巖土相互作用問題。FactorsofSafetyDependsonRequiredreliabilityConsequencesofafailureUncertaintiesinsoilpropertiesandappliedloadsConstructiontolerancesIgnoranceofthetruebehavioroffoundationsCost-benefitratioofadditionalconservatisminthedesign.0.75[]a0.75[]aAllowablestressdesign(useinthisbook)Thedesignloadisthemostcriticalcombinationofthevariousloadsources,asdefinedbycodes.ANSI/ASCE， D (2.1) D+L+F+H+T+(Lr

orSorR) (2.2) D+L+(LrorSorR)+(WorE) (2.3) D+(WorE) (2.4)3/14/20235（1）由可變荷載控制時：組合值系數(shù)c3/14/20236（2）由永久荷載控制時：組合值系數(shù)c3/14/20237ServiceabilityrequirementsIntendedtoproducefoundationsthatperformwellwhensubjectedtotheserviceloads.The

Requirementsinclude:SettlementHeave抬升TiltLateralmovementVibrationDurability3/14/20239MeasuresforalargesettlementAdjustthefoundationdesignUseamoreelaboratefoundationImprovethepropertiesofthesoilRedesignthestructuresoitismoretolerantofsettlements3/14/202310DifferentialsettlementsDefinitionThedifferentialsettlementisthedifferenceintotalsettlementbetweentwofoundationorbetweentwopointsonasinglefoundation.ReasonsforDifferentialsettlements:ThesoilpronotbeuniformacrossthesiteTheratiobetweentheactualloadandthedesignloadmaybedifferentforeachcolumn.Theratioofdeadloadtoliveloadmaybedifferentforeachcolumn.Theas-builtfoundationdimensionsmaydifferfromtheplandimensions.3/14/202311Whatisshallowfoundations?d/b<=2.5ShallowfoundationsThosetransmitstructuralloadstothenear-surfacesoil.Types:Spreadfootingfoundations(擴(kuò)展基礎(chǔ))Matfoundations（筏板基礎(chǔ)）dbdb3/14/202313Foundationswitheccentricormomentloads

One-wayloading

summary1.Shallowfoundationsarethosethattransmitstructuralloadstothenear-surfacesoils.Therearetwokinds:spreadfootingfoundationsandmatfoundations.2.Althoughothermaterialshavebeenusedinthepast,todayvirtuallyallshallowfoundationsaremadeofreinforcedconcrete.3.Spreadfootingsaremostoftenusedinsmall-tomedium-sizestructuresonsiteswithmoderatetogoodsoilconditions.Matsaremostoftenusedonlargerstructures,especiallythosewithdifferentialsettlementproblemsandthosewithfoundationsbelowthegroundwatertable.4.Thebearingpressureisthecontactpressurebetweenthebottomofashallowfoundationandtheunderlyingsoils.3/14/202317summary5.Afloatingfoundationisonewheretheweightofthefoundationissubstantiallylessthantheweightoftheexcavatedsoils.Thisoccursinbuildingswithbasementsandothersimilarstructures.6.Iftheloadsappliedtoafoundationareeccentric,orifmomentloadsareapplied,theresultingbearingpressuredistributionalsowillbeeccentric.Insuchcases,thefoundationneedstobedesignedsotheresultantofthebearingpressureiswithinthemiddlethirdofthefoundation(forone-wayeccentricity)orinadiamond-shapedkern(fortwo-wayeccentricity).Thisrequirementensurestheentirebaseofthefoundationhascompressivebearingpressures,andthusavoidsproblemswithuplift.3/14/202318第六章3/14/202319BearingcapacityfailurePunchingfailurecaseVeryloosesandAthincrustofstrongsoilunderlainbyaveryweaksoilWeakclaysunderdrainedconditionsFailuredevelopsgradually.3/14/202321BearingcapacityfailureLocalfailurecase-theintermediatecaseLoosetomediumsandsShearsurfacearewelldefinedunderthefoundation,andthenbecomevaguenearthegroundsurface.Failuredevelopsgradually.3/14/202322Example6.3A30-mby50-mmatfoundationistobebuiltasshowninFigure6.10.Computetheultimatebearingcapacity.3/14/202323Terzaghi’sbearingcapacityformulasAssumptions:D≤BNoslidingbetweenthefoundationandthesoil.Semi-infinitemassanduniformMCstrengthlawGeneralshearcaseNoconsolidationRigidfoundationSoilabovethefoundationbottomisNoshearstrengthCentralloading3/14/202325Terzaghi’sbearingcapacityformulas

3/14/202326

3/14/202329BearingcapacityonlayersoilsMethods:Evaluatethebearingcapacityusingthelowestvaluesofc',f'andg'inthezonebetweenthebottomofthefoundationandadepthBbelowthebottom.Evaluatethebearingcapacityusingtheweightedaveragevaluesofc',f'andg'inthezonebetweenthebottomofthefoundationandadepthBbelowthebottom.Rigorousanalysisuselimitmethod,similartoslopestabilityanalysis.3/14/202330第7章3/14/202331ThecausesofsettlementTheapplicationofstructuralloadsTheweightofarecentlyplacedfillAfallinggroundwatertableUndergroundminingortunnelingTheformationofsinkholesSecondarycompressionoftheunderlyingsoilsLateralmovementsresultingfromnearbyexcavations……Consolidationsettlement(NC)

Consolidationsettlement(OC-I)

Consolidationsettlement(OC-II)

EXAMPLE7.4TheallowablesettlementfortheproposedcontinuousfootinginFigure7.9is25mm.Uputeitssettlementanddetermineifitsatisfiesthiscriterion.

見課本224Settlementanalysesbasedonin-situtests

Schmertmann’sMethod

EsfromStandardPenetrationTest(SPT)resultsSoilTypeβ0(kPa)β1(kPa)Cleansands5,0001,200Siltysandsandclayeysands2,500600第八章3/14/202341Question:

canDbe0?MostoftheBearingCapacitywillbelost.easytobeundercutbyscour(沖刷),

especiallyonbridgepiers(橋墩)Thetopsoilusuallyispoorinstrength.Unabletoresisthorizontalload,orverypoorifany.Easytobeimpactedbytheweather.Frostheave（凍脹）

3/14/202342MakeDshallower,ifpossible

(bothbearingcapacityandsettlementaresatisfied.).Savetime,moneyandmaterial寬基淺埋MakeDabovethegroundwaterlevelinconstructionstage,ifpossible.OthergeneralprinciplestodetermineD3/14/202343TheinfluenceoftheadjacentbuildingsWhenanewfootingiscarriedoutnearaoldoneswhatwillhappen??

挖墻腳3/14/202344TheproceduretodevelopqABearingcapacityDthesmallestoneDw

TheshallowestoneFSafetyfactoragainstabearingfailure(PerFig.6.11)qaThesmallestappliednormalload.Bearing.xls,orqult_tzgorqult_vscSettlementdaanddDaAllowablesettlementandallowabledifferentialsettlementCh2dD/dTable7.5orlocalexperienceda=Min(da,dDa/(dD/d))由differentialsettlement算出來的允許沉降和由允許沉降的最小值。SettlementanalysisThelargestappliednormalloadSettlement.xlsorS4chmertmann.xls.keepd<da→q

3/14/202345Equivalentbearingpressuremethod

3/14/202346Example8.3GivenB=L=5ftD=2ftP=80kM=60ft-kqA=3500lb/ft2Dw=greatdepth.CheckSatisfactory?Solution3/14/202347試算法步驟：（1）進(jìn)行深度修正，初步確定修正后的地基承載力特征值fa。（2）根據(jù)荷載偏心情況，將按軸心荷載作用計算得到的基底面積增大10%~40%，即?。?）選取基底長邊l與短邊b的比值n（一般取n≤2），于是有國標(biāo)：2.偏心荷載作用要求：pk≤fapkmax≤1.2fae≤l/6（或pkmin≥0）基底最大壓力Designforshearloads

3/14/202350Example8.4GivenB=L=6ftD=2.5ftDw=greatdepthP=112kV=20kf'=29o(siltyfine-to-mediumsand)CheckOK?Solution3/14/202351Conditionsforfrostheave容易出現(xiàn)凍狀的土層ThereisanearbysourceofwaterThesoilisfrost-susceptible.Cleansandandgravel?×Clays?×Siltandfinesand?√Frostline凍深線3/14/202352第九章Spreadfootings

structuraldesign3/14/202353DesignloadsLRFDmethodFactoredloads3/14/202354Loadfactor,g

AmericanConcreteInstitute(ACI)CodeU=1.4D+1.7L (2.7)U=0.75(1.4D+1.4T+1.7L)U=0.9D+1.4FU=1.4D+1.7L+1.4FU=1.4D+1.7L+1.7H……U=1.4(D+T) (2.17)ANSI/ASCEandAISECodeU=1.4D (2.18)U=1.2(D+F+T)+1.6(L+H)+0.5(LrorSorR)U=1.2D+1.6(LrorSorR)+(0.5Lor0.8W)……U=0.9D+(1.3Wor1.0E) (2.23)3/14/202355summaryTheplandimensionsandminimumembedmentdepthofaspreadfootingaregovernedbygeotechnicalconcerns,andaredeterminedusingtheunfactoredloads.Thethicknessandreinforcementofaspreadfootingaregovernedbystructuralconcerns.StructuraldesignisgovernedbytheACIcode,whichmeanstheseanalysesarebasedonthefactoredload.Thestructuraldesignofspreadfootingsmustconsiderbothshearandflexural

failuremodes.Ashearfailureconsistsofthecolumnorwallpunchingthroughthefooting,whileaflexuralfailureoccurswhenthefootinghasinsufficientcantileverstrength.3/14/202356Sincewedonotwishtousestirrups(shearreinforcement),weconducttheshearanalysisfirstandselectaneffectivedepth,d,sothefootingthatprovidesenoughshearresistanceintheconcretetoresisttheshearforceinducedbytheappliedload.Thisanalysisignorestheshearstrengthoftheflexuralsteel.5.Oncetheshearanalysisiscompleted,weconductaflexuralanalysistodeterminetheamountofsteelrequiredtoprovidetheneededflexuralstrength.Sincedislarge,therequiredsteelareawillbesmall,anditisoftengovernedbyrmin.6.Forsquarefootings,usethesameflexuralsteelinbothdirections.Thus,thefootingisreinforcedtwice.3/14/2023577.Forcontinuousfootings,thelateralsteel,ifneeded,isbasedonaflexuralanalysis.Usenominallongitudinalsteeltoresistnonuniformitiesintheloadandtoaccommodateinconsistenciesinthesoilbearingpressure.8.Designrectangularfootingssimilartosquarefootings,butgroupagreaterportionoftheshortsteelnearthecenter.9.Practicalminimumdimensionswilloftengovernthedesignoflightlyloadedfootings.3/14/202358Ch10Mats(筏板基礎(chǔ))3/14/202359DesignmethodsRigidmethodstheconventionalmethod,theconventionalmethodofstaticequilibriumAssumption:ThematismuchmorerigidthantheunderlyingsoilsNoflexuraldeflectionBearingpressuredistributionislinear倒梁法DrawbacksoftheRigidmethodWidth-to-thicknessislargerformatfoundations.Notconsiderredistributionofbearingpressure.Cannotproducereliableestimatesofshears,momentsanddeformationsinthematNonrigidmethods

consideringsoil-structureinteractionWinklermethodCoupledmethodPseudo-coupledmethodMultiple-ParametermethodFiniteelementmethodTreatsoilsas“springs”Treatsoilsas“soil”WinklermethodLinearspringsNointeractionbetweensprings.Pseudo-coupledmethodSimilartowinklemodel,butHavedifferentksvaluesdependingontheirlocationks_outermost=2ks_innermost

summary1.Matfoundationsareessentiallylargespreadfootingsthatusuallyencompasstheentirefootprintofastructure.Theyareoftenanappropriatechoiceforstructuresthataretooheavyforspreadfootings.2.Theanalysisanddesignofmatsmustincludeanevaluationoftheflexuralstressesandmustprovidesufficientflexuralstrengthtoresistthesestresses.3.Theoldestandsimplestmethodofanalyzingmatsistherigidmethod.Itassumesthatthematismuchmorerigidthantheunderlyingsoil.whichmeansthemagnitudeanddistributionofbearingpressureiseasytodetermine.Thismeanstheshears,moment,anddeformationsinthematareeasilydetermined.However,thismethodisnotanaccuraterepresentationbecausetheassumptionofrigidityisnotcorrect.4.Nonrigidanalysesaresuperiorbecausetheyconsidertheflexuraldeflectionsinthematandthecorrespondingredistribution

ofthesoilbearingpressure.5.Nonrigidmethodsmustincludeadefinitionofsoil-structureinteraction.Thisisusuallydoneusinga"bedofsprings"analogy,witheachspringhavingalinearforce-displacementfunctionasdefinedbythecoefficientofsubgradereaction,ks.6.ThesimplestandoldestnonrigidmethodistheWinklermethod,whichusesindependentsprings,allofwhichhavethesameks.Thismethodisanimprovementoverrigidanalyses,butstilldoesnotaccuratelymodelsoil-structureinteraction,primarilybecauseitdoesnotconsidercouplingeffects.7.ThecoupledmethodisanextensionoftheWinklermethodthatconsiderscouplingbetweenthesprings.8.Thepseudo-coupledmethodusesindependentsprings,butadjuststheks

valuestoimplicitlyaccountforcouplingeffects.9.Themultipleparameterandfiniteelementmethodsaremoreadvancedwaysofdescribingsoil-structureinteraction.10.Theks

isdifficult

to

determine.Fortunately,thematdesignisoftennotoverlysensitivetoglobalchangesinks.Parametricstudiesareoftenappropriate.11.IftheWinkler

methodisusedtodescribesoil-structureinteraction,andthematgeometryisnottoocomplex,thestructuralanalysismaybeperformedusingclosed-formsolutions.However,thesemethodsaregenerallyconsideredobsolete.12.Moststructuralanalysesareperformedusingnumericalmethods,especiallythefiniteelementmethod.Thismethodusesfiniteelementstomodelthemat,anddefinessoil-structureinteractionusingtheWinkerorpseudo-coupledmodels.Inprinciple,italsocouldusethemultipleparametermodel.13.Adesigncouldbebasedentirelyonathree-dimensionalfiniteelementanalysisthatincludesthesoil,matandsuperstructure.However,suchanalysesarebeyondcurrentpractices,mostlybecausetheyaredifficulttosetupandrequireespeciallypowerfulcomputers.14.ThetotalsettlementisbestdeterminedusingthemethodsdescribedinChapter7.Donotusethecoefficientofsubgradereactiontodeterminetotalsettlement.15.Bearingcapacityisnotaproblemwithsandsandgravels,butcanbeimportantinsiltsandclays.ItshouldbecheckedusingthemethodsdescribedinChapter6.Ch11deepfoundationsG.Y.LUO3/14/202368definitiondeepfoundationisonethattransmitssomeoralloftheappliedloadtosoilswellbelowthegroundsurface.3/14/202369ApplicableconditionsTheuppersoilsaresoweakand/orthestructuralloadssohighthatspreadfootingswouldbetoolarge.Theuppersoilsaresubjecttoscourorundermining.Thefoundationmustpenetratethroughwater.suchasthoseforapier.Alargeupliftcapacityisrequired.Alargelateralloadcapacityisrequired.Therewillbeafutureexcavationadjacenttothefoundation.3/14/202370LoadtransferPiles(預(yù)制樁)DefinitionPilesareconstructedbyprefabricatingslenderprefabricatedmembersanddrivingorotherwiseforcingthemintotheground.TypeTimberpilesConcretepilesSteelpilesCompositepiles3/14/202372Drilledshafts(灌注樁)Drilledshaftsareanothercommontypeofdeepfoundation.Thefundamentaldifferencebetweenpilesanddrilledshaftsisthatpilesareprefabricatedmembersdrivenintotheground,whereasdrilledshaftsarecast-in-place.Type沉管灌注樁鉆（沖、磨）孔灌注樁挖孔樁旋挖樁3/14/202373AdvantageCompactionincreasesthestrengthandbearingcapacitySandyandgravellysoilsImprovingthesidefrictionresistanceLargebasesDisadvantageGeneratelargegroundvibrationEquipmentisbulkyCompactedshaftscannotincludelargeamountsofreinforcingsteel.ExpensiveEconomicalonlywhenthelengthislessthanabout9mPressure-injectedfootings(夯擴(kuò)樁)Ch13deepfoundations

axialloadcapacitybasedonstaticloadtestsFactorofsafetypiles≤Davisson’smethodP:kND:mmB:mmA:m2E:kPaExample13.3

Ch14deepfoundations

axialloadcapacitybasedonanalyticmethodsG.Y.LUO3/14/202379ChangesinthesoilduringconstructionPilesChangesinclaysDistortionCompressionandexcessporewaterpressureLossofcontactbetweenpileandsoilChangesinsandParticlerearrangement,crushing,anddensification.DrilledshaftsSide-frictionandtoe-bearingReductionNotethatforpiles,itisincrease(permanentally).DrillingmudSmearandremoldsImpactonAnalyticdesignmethodsMostoftheanalyticmethodsdescribedinthischapterareassociatedwithaparticulartypeofdeepfoundation.3/14/202380Toebearinginsands

effectivestressanalysis

3/14/202381

3/14/202382Clays

undrainedanalysis

3/14/202383Sidefriction

3/14/202384sands

3/14/202385

LateralearthpressurecoefficientSoil-foundationinterfacefrictionangle

SoilfrictionangleSandDifficulttodetermine.ClayEasytodetermine.3/14/202386sands

3/14/202387Gravels

3/14/202388Siltsandclays

3/14/202389Ch14deepfoundations

axialloadcapacitybasedonanalyticmethodsG.Y.LUO3/14/202390Increasedinloadcapacitywithtime孔隙水壓力的減少將導(dǎo)致承載能力的增加3/14/202391

3/14/202392Clays

undrainedanalysis

3/14/202393Sidefriction

3/14/202394

LateralearthpressurecoefficientSoil-foundationinterfacefrictionangle

SoilfrictionangleSandDifficulttodetermine.ClayEasytodetermine.3/14/202395sands

3/14/202396Gravels

3/14/202397Siltsandclays

3/14/202398

Piles

3/14/202399

Upwardloadcapacity

forfoundationwithenlargedbase3/14/2023100Upwardloadcapacity

3/14/2023101Load-SettlementResponse

3/14/2023102ImaginaryfootingmethodApplicableconditions:deepfoundationsunderlainbycompressiblesoilssuchthatthecompressionofthesesoilsismoresignificantthanthesettlementsrequiredtomobilizethesidefrictionandtoebearing.zi=0.67D:forfrictionpileszi=D:forend-bearingpilesLinearinterpolationforothers

3/14/2023103CH16Deepfoundation-lateralloadcapacityG.Y.LUO3/14/2023104Shortvs.longfoundationsShortfoundation:Thetoeisabletorotate.ThefailureiscontrolledprimarilybythesoilsLongfoundationThetoeisfixedThefailureiscontrolledprimarilybythefoundationFlexuralfailureFortimberpilesD/B>20Forsteelandconcretepile,D/B>353/14/2023105RigidanalysisAssumeEIisinfinite.NotaccurateasthenonrigidmethodUsedprimarilyforlightweightshortlateralloadedfoundationStreetlightsSmallhighwaysigns3/14/20231061.Alateralloadisanyloadthatactsperpendiculartothefoundationaxis.Thus,shearmomentarelateralloads,butaxialcompressionortensionortorsionalloadsarenot.2.Untilthemiddleofthetwentiethcentury,engineersassumedthatdeepfoundationswereonlyabletoresistaxialloads,sotheyusedbatterpilestoresisthorizontalloads.Morerecently,wehavereconsideredthatassumptionandnowrelyonbothaxialandlateralcapacities.3.Theutilizationoflateralcapacitiesindesignoftenproducesfoundationsthataremoreeconomicaltobuild