coastal management paper

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CHAPTER 1 5 6

AssessmentofCoastalProcessesfortheDesignandtheConstructionofthe

ZeepipeLandfallinZeebruggeir.A.EIDE,SeniorGeotechnicalEngineer STATOIL(Norway)

ir.B.MALHERBE,ProjectManager HAECONN.V.Belgium)ir.M.MERCANTI,SeniorPipelineEngineer SNAMPROGETTI(Italy)ir.B.LAHOUSSE,QAManager HAECON N.V.Belgium)ABSTRACT

Early1991,tatoilstartedwiththeinstallationofa40inchdiametergaspipelinebetweentheSleipnerandlaterTrollieldintheNorvegiansectorofheNorthSeaandtheharbourofZeebruggeontheBelgiancoast.TheonnectionetweenheffshorendhenshorepipelinewasperformedinAugust991,ntheandfallareaofZeebrugge.Thedesignandtheconstructionofthelandfallnheearshorereaequirednxtensivesurveyandengineeringprogramtakingtheenvironmentalparametersandthecoastalprocessesintoaccount.1.INTRODUCTION

TheZeepipeGasPipelineProjectforthedeliveryofnaturalasxtractedromheleipnerieldasapprovedbytheNorwegianarliamentnDecember986.DenNorskeStatsOljeselskapA.S.Statoil,tavangerNorway)stheoperatoronbehalfoftheZeepipeownersandisresponsiblefortheplanning,heconstructionandtheoperationoftheZeepipesystem.Zeepipesheargestffshoreipelayingrojectundertakenuptill1991.Approximately810kmof40",8kmof30"and230kmof20"pipelineswillgothroughtheNorwegian,anish,erman,utchandBelgiansectorsoftheNorthSea.Zeepipes pipelineystemorheransportfasfromheorwegianleipnerieldoeebruggenheBelgianCoast.

2 0 2 9


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2030 COASTALENGINEERING 992NorwegianNorthSea Gasgas pipelineStatfjord '3IfH|f8Kl;llexistingJOG u l l f a k s J8W?#llS5lSpilsunder\...Sbi'UlJlrjit-iigconst ruct ionuF^**~^V>


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ZEEBRUGGEZEEPIPELANDFALL 2 0 3 1

u >=3.ae m G -3.ee 2.5012.50 2.B0T II 2.00 1.58 m 11.50 1.00 -

1 1.00 0.75U 0.75 0.50 n s 1 0.50 e.25 r 10.25 e.ee 10.00 0.25 fcj -0.2E -0.5e-[/ , -8.50 -0.75 -\A -8.75 1.00 n- Y .' -\.ee 1.50 " V I -:.52 2.00L: -2.00 -2.50V * 2.50 -3.00Li


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2 0 3 2OASTAL ENGINEERING 1 9 9 2BathymetricurveyataererocessedsingdvancedDTM-processingDigitalerrainModel)nP-9000A D-computertoproducethecombinedsurveymaps.Paralleloheseathymetricurveys,llvailableexistinghydrographicdatafrom1980to1990andina5 kmwidecorridoralongZeepipewerecollecteddata-baseHaecon. V . )ndrocessedsifferentialapsodetermineaturalndan-madeecentorphologicalchangesoftheseabed(e.g.fig.3 )2.3.Geophysicalsurvey

Becauseoftheknownsoilheterogeneityandthelocalpresenceofoutcroppingtertiarygeologiclayers,shallowseismicsurveyhasbeenconductedinthesurveyedZeepipecorridorinordertopilotthegeotechnical/geologicsoilinvestigation.Ahalloweismicurveyasarriedutysingalternativelya50JEG&GMinisparkerandaThompsonPipeliner(3,5+7kHz)nordertooptimizepenetration.Theignificanteismiceflectorsressociatedwithimportantlayersforthedesign,i.e.a.herosionsurfacefheertiaryayersarkingtheransitionromertiaryoecentuaternarydepositsoftenassociatedwithgravel)b.verconsolidatedtertiaryclaylayersIncombinationwiththeshallowseismictracks,side-scansonarsurveyswereexecutedapparatus lein531T100kHz) EG&G260100kHz))nordertoidentifya.ossiblebstacleswrecks,ables,..)

significantobstaclesweredetectedb.orphologicottomeaturesuchsipples,and-waves,. .eflectingesidualed-loadransportdirections ipplendand-waveieldsrossing

ZeepipeatBolvanHeistSandbankcouldclearlybeidentified.

AlleophysicalataweredigitallyransferredoheHP-9000CADandIntergraph6040workstationforcombinedmapproduction.2.4.Geotechnical/geologicsurveys

Differentgeotechnical/geologicsurveyswithcoringsandpiezoconepenetrationtestingsPCPT)ereexecutedalongtheZeepiperouteintheoffshoreandonshorepartto ascertain/verify geophysical survey and to get


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ZEEBRUGGEZEEPIPELANDFALL 2033geotechnicalinformationforthedesignofthepipelayingandlandfallworks.Vesselsmobilisedforthesoilinvestigationincludetheself-elevatingplatformTijlI"HSS)ndheM.S.Bucentaur"(FarmandSurvey).Coringwasexecutedbycontinuoussamplingofthesoillayers(figure4).Piezoconepenetrationtestingwasdonetoinvestigatesoilconeresistance,sleevefrictionandpore-waterpressure eotechnicalarametersuchsfrictionngle,elativeensityndndrainedhearstrengthcouldbededuced.

ConeesistanceTHpa)

Figure4 xampleofgeotechnical/geologicsoilinvestigationresults.Coring+PCPTinthelandfallarea.

AllgeotechnicaldataweredigitallytransferredtotheHP-9000CA DandIntergraph6040systemfortheproductionofthecombinedsurveymaps.Inelectedoreholesirelineoggingsdensityndresistivitylogs)weredoneinordertoassessporosityanddensityfheoilayers.heseparametersreimportantfortheassessmentofsoilompactiondegreeandliquefaction potential.


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2034OASTALENGINEERING 9922.5.eochemical analysisDuringthegeotechnicalsurvey,soilsampleswerefrozenandstoredinafreezinginstallation.Accordingoheonventionfslo,hemicalcharacteristicsofthesampleswereanalysedinordertoassess ossibleontaminationnd/orontaminantremobilizationduringtrenching/dredging.Heavymetalandorganicompoundcontentswereoundtobebelowbasequalityreferencematerialcontents.2.6.Hydrometeoroloaicalconditions

VerticalidesremportantnhisartfheNorthSea.idesinZeebruggerangerom3,00mNeapTide)to5,00m(SpringTide).TheidalurrentsSW bb E lood)nrelationoheerticaliderehetrongestndhighestintheshallowpartsoftheNorthSeasuchastheBelgiannearshorearea.Offshorecurrentrosesareeitherellipticalrircularandnearshorenesreusuallybidirectional.hiseanshatffshoreatersconstantlyflowingwhilenearshorewatercirculationissimilartothatinanestuary.

StormsurgesmaybeparticularlydramaticnthispartoftheNorthSeabecauseofwindset-upcombinedwithheelativeighidalanges.ominantinddirectionsar eSW withNWforstormconditions.NW,NandNE-windstogetherwithatmosphericdepressionsareabletocauseconsiderablewindset-ups(upto2,00minextremeconditions).WaveactionisintenseintheSouthernBightduetoshallowaterepths,efraction,eflectionnddiffraction.egisteredaveharacteristicshowtypicallyshortperiodandsteepwaves.

3 .COASTALPROCESSES3.1.Tidalcrulleys

TheorphologicalvolutionnheearshorendlandfallareaisinfluencedbythetidalmechanismsintheNorthSea,bythedischargeoftheScheldtriverandalso,locally,bytheZeebruggeharbour.Longtermseabedvariationsareduetothecontinuousdevelopmentoftheebb andfloodgulleysystem.Ebb-andfloodgulleysareclosedinthedirectionoftheresidualsedimenttransport,aretypicallyapprox.4


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ZEEBRUGGEZEEPIPELANDFALL 2 0 3 5to10kmlong,pprox1to4kmwideandhavedepthsof0,50mto3,50mw.r.t.riginalseabed heyinteractcloselyandformahydrodynamicand physicalequilibrium.Floodulleysrehallowndorerequentloseoshore.Ebbgulleysaredeeperandlocatedmoreoffshore.3.2.Sandbanksandsandwaves

Theealandbanksocatednrontfheelgiancoastseemtobestablesandbodies.Duringstorms,omeofthemegaripplesandsandwavesontopofthebanksarecrest-cuttedbutsoonafterwardstheyarebuilt-upagain.Sandwaveheightisapproximately1,5mto2,5mandthewavelengthrangesbetween100and200meters.3.3.Turbidity maximumarea(TMA)andsedimenttransportThenearshoreareaischaracterizedbyamuchvaryingbottomlithologywithessentiallythepresenceofmuddytidalflatsC .DeMeyer,B.Malherbe1986).Intensivefieldmeasurementshavebeenexecutedinthispartfheortheainceeveralears.uchmeasurementsllowedostablish eneralesidualsedimenttransportpattern.igure5showsthevariationofidallevation,idalurrentsnduspensionconcentration.heyevealedhexistencefnencounterzoneofresidualedimenttransportsnfrontoftheBelgianCoastwhichresultsinamarineTurbidityMaximumArea(T.M.A.).t"

" '*\ / /-\ 4 \S > DEPTH |jV / \ t < l >\\ ^ / \VELOCITY Vm ! k t L \-r~ 1 'v /\N j \\ \ / \ ^ J \\ / i r\ V 1 \ * ~ -h J \ v ,, ^ f,vr,, 1 /* 4 OLID X > - .rs ^ 7 t CON CENTRATION >- ,% \.m '.> *m i m i .w e t TIMESCALE m i m . iW

Figure5 Simultaneousrecordingsoftidalelevation,tidalcurrentsandsuspensionconcentrationclosetotheLandfallArea.


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2 0 3 6OASTAL ENGINEERING 1 9 9 2TheT.M.A .scharacterizedbyaloosemuddepositlayer(thickness 0,50-1,00m)rappedwithintheT.M.A.Thevolumeofthisloosemudissignificantand mayamounttoseveralmillionsoftonsdrymaterial.TheT.M.A .entreofgravityisfurthermovinginfunctionoftheresidualflowandsedimenttransport.3.4.Beachstability

Theandyeachnheandfallreaouldesubjectedtomorphologicalchangesduetowaveresponse;thesemorphologicalchangesareunavoidablemodificationsinthebeachequilibriumprofile.Beforehextensionorksfheeebruggearbourstarted1977),heseabottomlevelwasalmostequaltoMSL7,00.fterwards,rogressiveccretionsedimentationasakenlacehichsueoumanactivitiesdisposalofdredgedmaterial)ndtonaturalsandccumulationtrappingfongshoreransportyeasterndamofZeebrugge).4.LANDFALLOFZEEPIPE DESIGNASPECTS4.1.Designcriteriaforthelandfall

TheifferentriteriasedorheesignfheZeepipeandfallreelatedoheollowingparametersa.eotechnicalstabilityofthepipelineb.oundationoffuturemarinadamswhichhavetocrosstheZeepiperoutec.epthofthemarinaaccesschannelandbasind.echnicalequirementsorrenching,redgingnd

pullingequipmente.idalgulleydevelopmentf.llowablestressesinthepipelineg.ipelaying/weldingrequirementsh. beacherosioni. riskanalysisofthepipeinrelationtonavigationj. authorityrequirementsThegeotechnicalstabilityisrelatedtotheliquefactionpotentialandthedifferentialsettlements.Liquefactionislikelytooccurifnoartificialbackfillofthetrenchisdone.Naturalbackfillwithsandisveryprogressiveandrepeatedliquefyingeffectsbyshortwaveactionmayconsequentlycauseprogressivepipelineupliftduringrenchilling.aturalackfillithoosemuddeposits (psat = 1,05 1,15) will generate more


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ZEEBRUGGE ZEE PIPELANDFALL0 3 7consolidatedmuddepositspsat=1,40 ,50)fterca.1r onths hisaysellauserogressivepipelineuplift.Thedifferentmarinamasterplansnhisreaoreseethebuildingofasanddunevisualbarrier)ndamarinadam whichwillbebuiltasarubble-moundbreakwaterwithafoundationofsoil-replacedsand.Thesandduneheight a.0m)slikelytocausethemostmportantettlementsupo,20) .ueoheheterogeneityofthequaternaryseabedsoillayersmud,sand,peat)differentialsettlementsaretobeexpected.Thefoundationofthemarinabreakwaterdamwillneedanexcavationfheaturaluaternaryoilayersithpoorbearingapacity.utteructionxcavationorkshaveoevoidednheloseicinityfeepipe.Becauseheres imitoherenchingepthfZeepipeanadaptedfoundationsolutionhasobeoundforthispartofthemarinabreakwater.Thearinaccess-channelndasindesignepthsgreaterthanTOP opofpipe)illhavetobedesignedinaccordancewiththeZeepipe"as-laid"profile.Thequipmentorherenching,redgingndipe-pullinerhavegivenwaterdepthrequirements,.e.ca.MSL-9,00m(CastoroIIpullingbarge VlaanderenXIXCSD).Therefore,heminimalrenchdepthsixedoMSL9,00m.Ascanbeseenonfigure3atypicalfloodtidalgulleyhasbeendevelopingclosetotheZeepiperoutesincetheendfheeebruggearbourWorks.uchidalulleydevelopmentsreollowedarefullyynterpretingdifferentialbathymetricmaps.Regardingthesoil-pipelineinteractionitcanbestatedthatthepipelineprofilewillinfluencethestressesintheipelinetself.hetressesayenducedytemperatureoads,nternalressureettlementssoildeformation) ,eismicaves,tc. .horoughtresscalculationsaveeenxecuted,akinghearticularsoilconditionsinthisareaintoaccount.Toxecutehedrytie-ininadryofferdam)fhespoolndheandfall-stringyelding aximumworkingdepthwithinthecofferdamof ,25mMSLwasrequired.Thismeansthatthetie-inpartofthelandfallhasbeendesignedatthatlevel.Beacherosionphenomenamayaffectthesubmarinebeachupto epthfa. ,50 SL.eachrosionndequilibriumslopecalculationswasdonetoevaluatebeach


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2 0 3 8OASTAL ENGINEERING 1 9 9 2responseohedesigntormconditions(waterevelwaveheightithe.g.. P.f0ears) .ecenteachevolutioncanalsobeassessedfromdifferentialmapping.Damagingrisksduringoperationandwithinlife-time50years)adoessessednrderoesignheappropriateovernd/orrotection.herefore isk-analysiswasexecutedtakingallexternalfactorssuchasnavigation,aintenanceredging,hip'sollision,tc...intoaccount.ThisriskanalysishasamajorrelevanceforthecrossingoftheScheurand Wielingennavigationchannels.Authorityequirementseferssentiallyoheoilconditionsafterpipeline-installationandthestabilityofhexistingarbournfrastructure.urthermorenenvironmentalimpactassessmentEIA)adtobedoneinrelationtotheplanneddredging,renchinganddumpingworksLDC/OSCON-convention).4.2.Landfalldesignalternatives

Thearrivalpointoftheoffshorepipelinewasfixed,i.e.heLandfallValveStationontheLNG-peninsulaoftheZeebruggeHarbour.Threemajorlandfallalternativeswereidentified1.ydirectionalrillingandubsequentipe-pullingfromseatoland2.ymicro-tunnellingwithapushedtunnelromshoretosea3.ith onventionalheet-piledofferdamorhe

shoreapproachincombinationwithacross-breakwatersolution.

Theriginalandfall-concepts,ydirectionalrillingormicro-tunneling,wereabandonedduetotheparticularsoilonditionsndheloseicinityfheockyrubble-moundbreakwater.Thelternativeonceptasicallyonsistsfconventionallandfall,withasheet-piledcofferdamintowhichheipeline,sulledashore.heipelinestiedintoaspoolpiecethatgoesthroughandabovethebreakwaterndhichonnectseepipeoheandfallValveStation.4.3.Trenching/dredgingofthepipeline

Inordertofulfillthedesign-criteriathepipelinehadtobetrenchedoverawidestretchofthenearshoreandshore-approacharea.


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ZEEBRUGGEZEEPIPELANDFALL 2 0 3 9IntheScheurshippinghannelherenchwasesignedtakingntoccountheisk-analysis,heoilconditionsithuaternaryandsndertiairyoverconsolidatedlaysndilts,heuthorityrequirementsandtheplansfordeepeningthechannel.nfigure heesignedrossingfhecheursillustrated.herenchingorksereesignedoeexecutedbyseagoingcuttersuctiondredgers.N .ille,F.Warnier,B.Lahousse-19 88).

IouthernUnitCenter theScheur)fScheur| NorthernUni t buoyUne jfScheur

"TA4"

5F3530 Isetoalcefleclore

buoyin e

Figure6 DesignofthecrossingoftheScheurshippinglanebyZeepipe.

InheWielingen"hippinganeheesignedpipelaying/trenchsesseephannhecheur.Thereforeacombinationofpredredgingtrailingsuctionhopperdredgers)ndpost-trenchingjettingsledgewithjet-barge)hasbeenforeseen.BetweenheWielingen"ndhehore 7 50 hore-approachtrenchupto 9mMSL(bottom width 50m)hasbeenesignedinitiallyox-cutndubsequently/7slopes).Theshoreapproachtrenchconnectstothesheet-piledcofferdam(figure7 ).Becauseofhedrytie-inofthepipelinentoaspoolpiecendheeedorxtraorkpace, emporaryartificialislandwasbuiltalongtheeasternbreakwater.Excavationworkswereexecutedwithinthecofferdamfora.onnectionbetweenoffshoretrenchandtie-inareab.oileplacementworkswithgravel)ecauseofhe

presenceofmuddysoillayers(coneresistanceQct


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2 0 4 0 COASTAL ENGINEERING 1 9 9 2

Figure7 horeapproachtrenchinsheetpiledcofferdamandartificiallandfallisland.

0 100 200 300 400 500 600 7 00 800 900HFigure8 ipelineprofileinthelandfallarea


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ZEEBRUGGEZEEPIPELANDFALL 2 0 4 1Inthiswaythepipelinewouldbeinasafeoperationalconditionfromastresspointofview,. e.below7 0%ofthespecifiedminimum yieldstrength.4.4.BackfillofthepipelinetrenchTovoidamagingisksfheipelineueonavigationhazardstrailinganchors,unkenships,tc...)nd/oraintenanceredging, ontinuousravelcovergraveliameter ,11)fheipelineasdesignedintheScheurcrossingarea.Thedesignofthebackfilloftheshoreapproachtrenchinheransitiononebetweenpre-trenchingandpost-trenchingdoesfulfillthecriteria,relatedto,a.o.

pipelinestabilityagainstliquefactionandflotationauthorityrequirementsThebackfillwasdesignedbyaseriesofseparatedgravelbermsalternatingwithsandbermsfigure9)nordertooptimizethebackfillcosts.Thegravelsolutionwasretainedbecausea .toffersabettersolutionagainstliquefaction(toensureverticalstability)b.treducesexecutionproblemsifthetrenchisfilledwithloosemuddeposit.

Figure9 Scheme of backfill of the shore-approachtrench.


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2 0 4 2OASTAL ENGINEERING 1 9 9 2Thebackfilloperationsweredesignedtobeexecutedbysplithoppersandside-dumpingvessels.4.5.Crossing-ofthebreakwater

Forthecrossingofthebreakwatertheupperlayersofheubble-moundtructureadoearefullydismantled,akingintoaccounttheas-builtdrawingandtheoundationfheamsoileplacement,illow-matrass,erm).nheermandreakwaterrossingsandasphaltcoreinwhichthespoolpieceisbeddedhasbeendesignedthicknessofsandasphaltunderandabovepipeca.1m).5.ZEEPIPELANDFALLCONSTRUCTION

Inordertoexecutethepullingashoreoperationincontrollednvironmentalonditions,heetpiledcofferdam hasbeenconstructedfirst.Thelandwardendofthecofferdamhasbeendriveninatemporary artificial island. The purpose of thistemporaryislandwastoprovideaprotectionagainstseaconditionsduringtheopeningofthebreakwaterandtheinstallationofthespoolpieceacrossthebreakwater.Atrenchhasbeenexcavatedwithintheofferdam,ntowhichhepipelineaseenpulledashoreromalatbottomlaybargebywinchesplacedonthebeach.Theislandhasthanbeusedasaworkplatforminfrontofthetrench.Afterthepipelinewaspulledashore,hecofferdamhasbeenpluggedwithclayanddewateredallowingthetieinoperationtobedoneindryconditions.Theeawardndofheofferdamhaseenilledwithseagravelandsand.Finallythepipelinehasbeentied-intoaspoolpiecethathasbeenlaidacrossthebreakwaterpreviously.6.REFERENCES

Chr.P.DeMeyer,B..Malherbe.Terraetaquanr.35."Optimizationofmaintenanceredgingperationsnmaritimeandestuarineareas."N.Pille,F.Warnier,B.Lahousse.Antwerp20-24June1988."Thesefredgingquipmentorrenchingndcoveringofoffshorepipelines."K.VIV9thInternationalHarbourCongress,L.Stolberg.August1992"Norway'sZeepipeProjectmeansmoregasforEurope"Pipeline&GasJournal

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