DatabaseAssessmentofCPT-BasedDesignMethodsforAxialCapacityofDrivenPilesinSiliceousSandsJamesA.Schneider1;XiangtaoXu2;andBarryM.Lehane3Abstract:NumerousconepenetrationtestCPT-basedmethodsexistforcalculationoftheaxialpilecapacityinsands,butnoclearguidanceispresentlyavailabletoassistdesignersintheselectionofthemostappropriatemethod.Toassistinthisregard,thispaperexaminesthepredictiveperformanceofarangeofpiledesignmethodsagainstanewlycompileddatabaseofstaticloadtestsondrivenpilesinsiliceoussandswithadjacentCPTprofiles.Sevendrivenpiledesignmethodsareconsidered,includingtheconventionalAmericanPetroleumInstituteAPIapproach,simplifiedCPTalphamethods,andfournewCPT-basedmethods,whicharenowpresentedinthecommentaryofthe22ndeditionoftheAPIrecommendations.Meanandstandarddeviationdatabasestatisticsforthedesignmethodsarepresentedfortheentire77piledatabase,aswellasforsmallersubsetdatabasesseparatedbypilematerialsteelandconcrete,endconditionopenversusclosed,anddirectionofloadingtensionversuscompression.Certainmethodsareseentoexhibitbiastowardlength,relativedensity,conetipresistance,andpileendcondition.Othermethodsdonotexhibitanyapparentbiaseventhoughtheirformulationsdiffersignificantlyduetothelimitedsizeofthedatabasesubsetsandthelargenumberoffactorsknowntoinfluencepilecapacityinsand.ThedatabasestatisticsforthebestperformingmethodsaresubstantiallybetterthanthosefortheAPIapproachandthesimplifiedalphamethods.Improvedpredictivereliabilitywillemergewithanextensionofthedatabaseandtheinclusionofadditionalimportantcontrollingfactorsaffectingcapacity.DOI:10.1061/ASCE1090-02412008134:91227CEDatabasesubjectheadings:Drivenpiles;Conepenetrationtests;Foundationdesign;Compression;Sand;Pileloadtests;Databases.IntroductionThestaticaxialbearingcapacityQtofadeepfoundationisgivenasthesumoftheshaftcapacityQsandbasecapacityQb:Qt=Qs+Qb=Pztip−Lembztipfdz+qbAb1whereP=pileperimeter;f=localultimateshaftfriction;qb=ultimateunitbaseresistance;Ab=pilebasearea;ztip=tipdepth;andLemb=embeddedpilelength.Thevalueofqbwhichiszeroforapileloadedintensionisnormallylimitedtothatmobilizedatapiletipsettlementof10%ofthepilediameter.Awiderangeofempiricalapproachesarecurrentlyusedtocalculatefandqbfordrivenpilesincoarsegrainedsoils.ThisrangehasarisenbecauseoftheinadequacyofexistingtheoreticalmethodsforpredictionofthesoilresponseduringandafterpileinstallationcoupledwiththelargenumberofvariablesknowntoaffectpileaxialcapacitiesinsandRandolph2003.Further,Den-nisandOlson1983concludedthatwhilesoildensityinfluencesshaftfrictionandbasecapacityofopen-endedpiles,interpretationoftheinfluenceofdensityishighlyuncertainduetopoordefini-tionofsoilpropertiesalongthelengthofapile.UseoftheconepenetrationtestCPTforsitecharacterizationprovidesalargeamountofrepeatableinformationontheverticalvariabilityofsoilstrengthandcompressibilityandthereforeleadstoincreasedde-signreliabilityi.e.,BriaudandTucker1988.Thispaper,aswellasadditionalparametricstudiespresentedbyLehaneetal.2005aandSchneider2007seektoassistdesignersinmakinginformeddecisionsregardingaxialpilecapacitybasedonanun-derstandingofthebasisofagivenempiricalapproachandoftheassociatedrelativelevelofuncertaintyandbias.Althoughsitespecificstaticanddynamicloadtestsreducethelevelofuncertaintyforonshorepractice,loadtestsarepro-hibitivelyexpensiveintheoffshoreenvironmentandrelianceisplacedonextrapolationofempiricalcorrelationsderivedforon-shoreapplicationsMcClellandetal.1969.Althoughthederiva-tionoffandqbinEq.1foroffshorepilesinsandhashistoricallybeenbasedon“visualclassificationmethods”placedwithinframeworksofbearingcapacitytheoryandanearthpres-sureapproachMcClellandetal.1969,fourCPT-basedmethodsarenowincludedinthecommentaryofthe22ndeditionoftheAmericanPetroleumInstituteAPIrecommendedpracticeRP2AforfixedoffshorestructuresAPI2006.TheCPTisoftenthoughtofasamodelpileandhasalonghistoryofuseforestimationsofstaticaxialpilecapacityDelft1936.Thereis,however,awidevariationofCPT-baseddesignmethodsinuse1Ph.D.Student,SchoolofCivilandResourceEngineering,TheUniv.ofWesternAustralia,Crawley,PerthWA6009,Australiacorrespondingauthor.E-mail:schneider@civil.uwa.edu.au2Ph.D.Student,SchoolofCivilandResourceEngineering,TheUniv.ofWesternAustralia,Crawley,PerthWA6009,Australia.3Professor,SchoolofCivilandResourceEngineering,TheUniv.ofWesternAustralia,Crawley,PerthWA6009,Australia.Note.DiscussionopenuntilFebruary1,2009.Separatediscussionsmustbesubmittedforindividualpapers.ThemanuscriptforthispaperwassubmittedforreviewandpossiblepublicationonJune15,2006;approvedonOctober29,2007.ThispaperispartoftheJournalofGeotechnicalandGeoenvironmentalEngineering,Vol.134,No.9,September1,2008.©ASCE,ISSN1090-0241/2008/9-1227–1244/$25.00.JOURNALOFGEOTECHNICALANDGEOENVIRONMENTALENGINEERING©ASCE/SEPTEMBER2008/1227worldwidee.g.,DeCocketal.2003becausethefactorscontrol-lingaxialpilecapacityareinfluencedbymoresoilparametersthanthoseaffectingtheCPTtipresistance,qc,e.g.,Lehaneetal.1993.Empiricaldesignmethodsrelyoncalibrationwithdatabasesofstaticload