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A Comprehensive Study of Pile Foundations in Coral Fomations and Calcareous Sediments

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   JKA C·  ~·llg S I Vol.   pp. 3 17 I Ho \ II pllHl \   I AComparativeStudyofPileFoundationsinCoralFormationsandCalcareousSediments FOUAD M. GHAZALI ZAKI A. BAGHDADI AND OSAMA A. MANSUR CivilEngineeringDepartment Faculty of Engineering King  bdulaziz University Jeddah;Military  orks - JeddahBranch SaudiArabia ABSTRACT Great difficulties are usually encountered in the design of pilefoundationsinmarine strata.These difficultieshavebeen attributed mainly to theheterogenous nature andunusual behavior of these strata. Quite commonly, the marine strata havelowbulkdensity and usuallyconsist of weakly cemented calcareous andcarbonate soils interbedded withcoralrockcontainingcavitiesfilledwithcoraldebris.Geotechnicalinvestigationsshow that conventionalsoilmechanicstechniquesarenotsuccessfullyapplicableto these formations and sediments.This paper presents acasestudy of a proposed foundationdesignfora380mlongquay.This quay  s to beconstructed near the city ofJeddahon theeastcoast of the Red Sea. The initial proposed designby the designersuggested60cm square precastconcretedrivenpiles.Thisproposalwasnot satisfactory tothe geotechnical consultantof the contractor and insteadhe recommended boredand grouted piles.This recommendation wasbaseduponfield data loadtesting of piles and informationavailableintheliterature.Acriticalevaluation ofboth the proposed designaswellasthealternative put forwardby the contractor,isgiveninthis paper alongwithre commendations envisagedbytheauthors. Introduction The basicformations of theeasterncoast of Red Sea,betweenlatitudes 30 degreessouthand 30 degreesnorth,arecalcareousdepositsandcora reef rocks.Calcareousdepositsaremainlycomposed of calciumcarbonate  CaC0 3  whichareformedbyshells and skeletalremainsofbenthosorganismssuchascorals,molluscas,andcalcareousalgae.Coralreefrocksareformations of calciumcarbonatelaiddownbylivingmarineplants corallinealgae andmarineanimals,corals[l].Withtime,  y precipitationandrecrystallization,coralsbecamemoredenseandrock-likeandarethenknownascoralreefrock.Detailedmineralogicalanalysisby x ray diffractionshowedthat,  n recent samples of coralreefrocks, CaC0 3 existedentirelyintheform of aragonite,whereasoldersamplesgenerallycontainedsomecalcite;thegreater 3  4  ouad   Ghazalietal theage, the higherwas the percentage of calcite[2]. Dueto unusualbehaviourofcoralandcalcareousdepositsandlack of satisfactoryengineeringtechniquesanddesigntheoriesregardingsuchformations,designers of pilefoundationsinthistype of strata facegreatdifficultiesandproblems.Theseproblemsincreasewhensuchstratahaveaheterogenousnature,asinthecasealong the easterncoast of Red Sea.   comparativeandcriticalevaluation of twodesignmethods of pilefoundationinheterogeneouscoralsandcalcareousdepositsispresentedinthis paper withanat tempt forbetterunderstanding of thebehaviour of pilefoundationsincalcareousandcoralformations.Acasehistory about thedesign of pilefoundationsincalcareousandcoralformationsandpileloadtestsinJeddah area ontheeasterncoast of the Red Seaarepresented.Thispiledesign is forashiprepairquay380meterslong and  4 meterswide,withacraneontop and alongit,whichwilltransportamaximumload of 60tons.Twopartiesareinvolvedinthiscasehistory in whichpartyD  De- signer)proposed400drivenprecastconcretepileswhile part C(Contractor)proposedanalternative method onthebasis of hisownanalysis of siteinvestigation  ~ theresults of thepileloadtests. The views of thetwopartiesarepresentedinthispaperalongwiththeauthors comments,criticalanalysisandrecommendations of thiscasehistory.Geological and EngineeringInformationAbriefdescription of thegeologicalaspects of theeasterncoast ofRed Seaingeneral,andthesiteoftheprojectinparticular, is presented. The easternRedSeacoast is characterizedby three mainfeatures.Firstarethenumerouscoralreefs,fringingsandbarriers, that stretchparallel to thecoast.Theseformationscontaincavitiesfilledbycoraldebris eroded bywaveaction.Secondfeatureistheseafloorbetweenthecoralheadsandreefswhichiscoveredwithmarinesediments. The marinesedimentsconsist of loosetomediumdensecarbonatesands,silts and clayswithlayers of coral. The thirdfeatureis the coastalplainwhichcontainsalluvialsoilfromtheArabianshield(gravel,sand and silts)underlying and in- termixingwiththe reef depositsandmarinesediments. The geology of theprojectareaconforms to thegeneralfeaturesoutlinedearlier.Twolithologicunitsarepresentinthesitearea. An alluvialfanconsisting of mixtures of sand,clay and siltwithdebris of shellsandcorals.Underlyingthealluvia,existsacoral reef formationconsisting of asurficialcoral reef andan older buriedcoralreef.Disintegrationproducts of thereefsfill the cavities in thereefsandcovertheslopeswithblankets of skeletalsandandsilts. It should be pointed,outthatgeologicalobservationcouldprovideessentialunderstanding ofthe engineeringbehaviour of thesoils under study. Deshmukh   ale  ] listsomepointsto be observedregardingcorals:   Origin of skeletalsystem:thisconcernstheshape and size of corallitesexaminedandwhethertheirwallsareperforate or imperforate. 2 Ageofthe coralreef:oldercoralreefsexhibit greater lithification,higher  ComparativeStudy of PileFoundations   5 strength,lessvoidratioandlesspermeability.3 Type of reef:oceanicreefsshowhigherstrengthandlowerpermeabilitythancontinentalreefs.4 Zonation:testsindicatethatcoralsonexposedsides windward arelikelytohavebettergeotechnicalpropertiesthanlagoonal or inexposedzones.Allavailablegeotechnicaldataonmarineformationshaveemphasizedtheirheterogeneousandirregularstratification.Alluvial,calcareousandcarbonatesoilsalongwithcorallimestonesareusuallyfoundincoastalzones.Thisdictatesthatsubsurfaceboringsshouldbespacedascloselyaspossible.Calcareoussedimentshavebeenreported[1,3]toexhibitweakcementation,highvoidratiosandhighmoisturecontentswithlowbulkdensities.Surveyofliterature on marinestructureshasindicatedthatpilefoundationsareprobablythemostsuitableforthiskind of projects l4 ]. Ithasbeenfoundl 1,3] thatbearingcapacities of drivenpilesincalcareousandcoralformationscalculatedfromconventionalgeotechnicalproceduresaresignificantlyhigherthanthemeasuredvaluesleadingtounconservativedesigns.Examinations of pileloadtestshaveledtorecommendlimitingvalues of skinfriction of 2t m   and pointbearing of 200to600 t m 2l3  7   Itshouldalsopointed out thatboredandgroutedpilesoffered 3 5 timeshigherbearingcapacitythandrivenpiles of the samediame ter l1 ]. Furthermore,piledrivingcausescollapse of theweakcementationanddestruction of coralstructuresleadingtolowerlateralpressureandpointbearing l8 ] Increasingpenetrationlength or enlargingthe end baseofthedrivenpilemaynotappreciablyimprovethebearingcapacity.Standardpenetrationtestshave been utilizedtodevelopapiledesignprocedurewithlimitingvalues of frictionandbearingonthebasis of investigationsexecutedalongthe Red Seacoast of SaudiArabia l4  5] asshowninFig. 1 and 2inwhichgoodestimation of pilebearingcapacitywasobtainedbypileloadtests. .....N 25  1 -E   :::::>z LL   20 V B = DIAMETER ~   11 OFPILE  > z 15 -I--+--- --.....~_.-.-.... ------t------ ~ Q I CARBONATE SOIL l . Dc = 108 >   AND CORAL U C 10   z a -LL J   t:: z 5 L I   ~ - V IFI ~   u -   5  ii ...J lJ I 0 I  ~IL o 20406080 100 STANDARDPENETRATIONRESISTANCE N IN BLOWSPERFOOT FIG. 1. Limitingunitskinfrictionagainst N values. Hagenaar  5 .  6  ouad M. Ghazalietal STEELPIPEPILEDRIVEN .8- CLOSEDENDED o10-0PEN ENDED 3 D/ e :7.6 1 ,000..,.. ............ -....--...-- ....  .. .. · .... --*-....- o 50 100 STANDARDPENETRATIONRESISTANCE, N, IN BLOWS PERFOOT 1 0,000 ,...-..,..--oor-~~ -ifE;ff:iii. ~8e 5,000 ... ~~~~  --- - --- 3.000 2,OOO - ~~ w u z <{ I- til Vi w a: t z o   I N W E ........... <t z ~~   ..J   ::::>tT FIG. 2. Ultimatepointresistanceversus N values.Hagenaar 5 . At thesiteunderconsideration,party  D conductedsubsurfaceandgeotechnicalinvestigationthatincluded: 1 Drillingthreeoffshoreandtwoonshoreboringstodepthsrangingsfrom 25 40m,running8PTandcollectingsamples.2 Jetting 19 jetboringstodeterminethedepthofsoftsediments. 3 Performingstaticconepenetrationtestsupto23mdepth. 4 Conductinglaboratorytestsincludingsoilclassificationonsamplesobtainedfromboreholes,directshearbox,unconfinedcompressiontestsandchemicalanalysis of thesoils.Examination of theborelogsindicatedthattheprojectareaconsists of twozones:northernandsouthern.Thenorthernzone,Fig.3, is lessfavourable,sincenohardstratum is encountered.Thesouthernzone,Fig.4, is morefavourabletothepiledesignsinceahardstratum of corallimestone is encountered. FIG. 3. Typicalstratainthenorthernzoneoftheprojectarea by partyD. E o CW o   In ããã   III   ,ããã  . rããã   · .... .., . , . . ãã, ãããããã II . . : :. ..... '.~ ããã4ã . . , . .. .   ..... · .   . . ~.~ ..   .. ã, I t ã .  .   ..,. . VERYLOOSE TO DENSECARBONATESILTYSAND (N = 10)MEDIUMDENSESANDYSILT  BROWN)  N = 15) DE NSE TO VERY DENSE SILTYSAND

Ch3

Jul 25, 2017
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