hydraulic conductivity of steel pipe sheet pile cutoff walls at coastal waste landfill sites _...

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HydraulicConductivityofSteelPipeSheetPileCutoffWallsatCoastalWasteLandfillSites

ShinyaInazumi1

[1]KyotoUniversity,Japan

1.Introduction

Landfillsitesarefacilitieswherethefinalresidueisdisposedafterallpossiblerecyclingenergyhasbeen

recoveredfromit.Therefore,landfillsitesareanimportantpartofcivilinfrastructure,requiredfor

environmentalconservationwithoutdumpingwasteinresidentialareas.However,inmanycases,theconstruction

oflandfillsiteshasbeenopposedduetoconcernsofresidentslivingthevicinityregardingenvironmentsafety

withregardtosituationssuchastheleachatefromwastemayleakouthence,theconstructionofnewlandfill

siteshasbecomemoredifficult.Moreover,theconstructioncostoflandfillsiteshasalsosignificantlyincreased

simultaneouslyduetotighterenvironmentallegislation(Shimizu,2003Kamonetal.,2007).

InJapan,smallscaleinlandlandfillsiteswereoftenconstructedintheriverheadareasofmountainvalleys.With

regardtotheabovementionedsocialconcernsregardingthelandfillsites,thelocationsoflandfillshaverecently

beendiversifiedintocoastalareasonalargescale.Thesesitesaredevelopedaturbanharbourareasinorderto

reducetheriskofcontaminatingthegroundwater,whichcanbecausedbytheleakageofleachate,andconserve

thewaterresources(Kamon&Inui,2002).Inthenationalstatisticsof2003announcedatMinistryofthe

Environment,thecapacityofcoastallandfillsiteswas23.3%ofthatofalllandfillsites,andparticularlyin

metropolitanareas,itwasgreaterthan80%(seeFig.1).Thesestatisticsindicatethattheroleofcoastallandfill

siteshasbeenincreasingsteadily.However,theresidentslivinginthevicinityofthesesitescontinuetoexpress

thesameconcernsforenvironmentsafety.Therefore,ensuringstableandsystematicoperationofthecoastal

landfillsitesinthefutureandprolongingthelifeofcoastallandfillsitesconstructeduntilnowareimportant

mattersofconcern,particularlyinmetropolitanareas.

Arevetmentatacoastallandfillsiteensuresspaceforwastedisposalandharbourmaintenanceduringthedisposal

ofwaste,constructionsludge,dredgedsoiletc.Arevetmentatacoastallandfillsitemustfunctionasavertical

(side)cutoffbarrierthatpreventstheleakageofleachatecontainingtoxicsubstancesfromthelandfillwaste,into

theseafurthermorerevetmentsmustprotectthecoastallandfillsitefromvariousexternalforcessuchas

earthquakes,oceanwaves,hightidesandtsunamis(WaterfrontVitalizationandEnvironmentResearch

Center,2002).

Recently,steelpipesheetpiles(SPSPs),usingwhichthedeepwaterconstructionispossible(Japanese



AssociationforSteelPipePiles,1999),havebeenwidelyemployedinverticalcutoffbarriersatcoastal

landfillsitesduetotheirworkabilityandeconomicalefficiency.A



FIGURE1.Capacitycomparisonbetweeninlandandcoastallandfillsitesbasedonnationalstatisticsof2003announcedat

MinistryoftheEnvironment,Japanitleoffigure,leftjustified

verticalcutoffbarrieremployingSPSPsiscalledaSPSPcutoffwallinthisstudy.However,thedesignand

applicationofSPSPcutoffwalls,evaluationofenvironmentalfeasibility,constructiontechnologyandlongterm

maintenanceareverycomplicatedbothexperimentallyandanalytically(Kamonetal.,2001).Thisisbecause

oftheexistenceofjointsectionsintheSPSPs,asshowninFig.2.

TheappropriatelyestimationofthehydraulicperformanceofSPSPswithjointsections(showninFig.2)isan

importantissue,particularlyintheevaluationofenvironmentalfeasibility,thatis,thecontainmentofleachates

containingtoxicsubstances.Figure3showsthecharacterizationoftheenvironmentalfeasibilityofverticaland

bottomcutoffbarriersaswellastheoveralllandfillsite.WhenevaluatingthehydraulicperformanceofanSPSP

cutoffwall,anequivalenthydraulicconductivityisgenerallyobtained(WaterfrontVitalizationand

EnvironmentResearchCenter,2002).Thisequivalenthydraulicconductivityassumesthatthejointsection

andthesteelpipeareintegratedtherefore,thehydraulicconductivityissubstitutedwithauniformpermeable

layer(seeFig.4).ThePrimeMinistersOfficeandtheMinistryofHealthandWelfaresaysthattheintegrated

equivalenthydraulicconductivitywith50cmthicknessmustbe1.0106cm/sorless(WaterfrontVitalization

andEnvironmentResearchCenter,2002).However,inanevaluationthatemploystheequivalenthydraulic

conductivity,itisdifficulttoconsiderthelocalleakageofleachatecontainingtoxicsubstancesfromthejoint

sectionsintheSPSPcutoffwall.

Inthisstudy,anevaluationmethodthatcanexpressthelocalleakageofleachatefromthejointsectionsinthe

SPSPcutoffwallsisdiscussed.Inparticular,theevaluationoftheenvironmentalfeasibility(containmentof

leachatescontainingtoxicsubstances)consideringa



FIGURE2.Schematicdiagramofsteelpipesheetpileswithjointsections



FIGURE3.Characterizationofenvironmentalfeasibilityonverticalandbottomcutoffbarriersaswellasoveralllandfill

site

threedimensionalarrangementandhydraulicconductivitydistributionofthejointsectionsintheSPSPcutoff

walliscomparedwithanevaluationthatusestheequivalenthydraulicconductivity.

2.Analysisforenvironmentalfeasibility

Thedevelopmentofmethodsforthedetectionofthegenerationpointsofleachateleakagehasbeenconductedin

variousdifferentwaysatinlandandcoastallandfillsitesinordertodeterminewhentheleachatecontainingtoxic

substanceswillleakintothesurroundingareasafterthelandhasbeenreclaimedatthelandfillsite(Kamon&

Jang,2001TheLandfillSystem&TechnologiesResearchAssociationofJapan,2004).However,the

presentdetectionmethodsareinsufficientwithregardtotheirdurability,andtheuseofthesemethodsmaylead

toexcesscostandtimeforrepairingthegenerationpointsofleachate



FIGURE4.Conceptofequivalenthydraulicconductivityassumingthatjointsectionandsteelpipeareintegrated

leakageintheverticalandbottomcutoffbarriersatthelandfillsites.Therefore,aneffectiveimplementationand

verificationoftheseepageandadvection/dispersionanalysis,consideredasatwodimensionalorathree

dimensionalproblem,oftheleachingbehaviorofleachatecontainingtoxicsubstancesarenecessaryalongwith

theupgradationofthetechniqueusedtorepairverticalandbottomcutoffbarriers.Thestructureofverticaland

bottomcutoffbarriersthatcanensurelongtermstabilityaswellastheevaluationmethodfortheenvironmental

feasibilityoflandfillsitesmustbealsodiscussed.

Theleachingbehaviorofleachatescontainingtoxicsubstancesneartheverticalandbottomcutoffbarriersat

landfillsitesmustbeconsideredwithregardtonotonlyinfiltrationbutalsotheadvectionanddispersion

phenomena(Kamonetal.,2007).Therefore,thesephenomenamustbeaccuratelyreproducedinthe

implementationoftheseepageandadvection/dispersionanalysis.Inthisstudy,theinfiltration,advectionand

dispersionphenomenamustbeexpressedthreedimensionallyinordertoaccountforthejointsectionsinthe

SPSPcutoffwalls.Also,theanalysisofcoastallandfillsites,unlikethatforinlandlandfillsites,mustconsider

theeffectoftides,etc.Furthermore,eachverticalandbottomcutoffbarrierisacompositestructureconsistingof

syntheticfiber,steel,rubbleandtheseabedthiscompositestructuremustbereproducedaccurately.

TheEulerianLagrangeanfiniteelementmethodisanumericalcalculationmethodthatisknowntobeusefulin

efficientlyreproducingsuchcomplicatedphenomena.Inthisstudy,theseepageandadvection/dispersionanalysis

isperformedusingDtransu3D/EL,whichisusedasarepresentativeanalysiscode(Nishigakietal.,1995).

2.1.OBJECTIVEANDASSESSMENTINDEXInanSPSPcutoffwall,jointsectionsarearrangedbetweensteelpipes,formingathreedimensionalstructure



(seeFig.2).Therefore,itisnecessarytoaccuratelyreproducethelocalleakageofleachatesfromthejoint

sectionsfortheevaluationoftheenvironmentalfeasibilityoftheSPSPcutoffwall.Inthisstudy,theleachate

containmenteffectoftheSPSPcutoffwallisevaluatedbyusingathreedimensionalseepageand

advection/dispersionanalysis(Dtransu3D/EL).Thisanalysisreproducestheexistenceofjointsectionsmore

precisely.

Figure5showsthethreedimensionalcrosssectionofalandfillsiteassumedasabasiccaseinthisanalysis.The

SPSPcutoffwallaswellasapartofthecompositionlayerarounditin



FIGURE5.Threedimensionalcrosssectionoflandfillsiteassumedasabasiccaseintheanalysis

thecoastallandfillsiteisconsideredforsettingthethreedimensionalcrosssection.Atthebottomofthewaste

layeraswellasintheseabed,aclaydepositlayerisassumedtoexist,andthislayerfulfilstheroleasabottom

cutoffbarrierinthecoastallandfillsite.TheSPSPcutoffwallispenetrateduptoadepthof3mintheclay

depositlayer,andthehydraulicconductivityoftheSPSPcutoffwallisvariedtoprovidedifferentexamination



cases.

IntheconstructionoftheSPSPcutoffwallatcoastallandfillsites,doubleSPSPcutoffwallsmaybeuseddueto

ensuremechanicalstabilityandfailsafeconceptoflandfillsites,asshownintheoverviewinFig.6.

Furthermore,theclaydepositlayermaybeimprovedbysandcompactionpile(SCP)methodsinordertoenhance

themechanicalstabilityoftheSPSPcutoffwalls(WaterfrontVitalizationandEnvironmentResearch

Center,2002).However,themainobjectiveofthisstudyistheevaluationoftheenvironmentalfeasibility

(containmenteffectofleachatecontainingtoxicsubstances)oftheSPSPcutoffwall.Therefore,thecoastal

landfillsiteissimplified,asshowninFig.5,asathreedimensionalcrosssectionthatcomprisesasingleSPSP

cutoffwall,wastelayerandclaydepositlayer.Thethreedimensionalcrosssectionassumestheextreme

conditionsfortheverticalandbottomcutoffbarriersthatwouldposeenvironmentalpollutionriskstothe

surroundingsaffectedbycoastallandfillsites.

FIGURE6.Overviewofverticalandbottomcutoffbarriersgenerallyconstructingatcoastallandfillsites



TABLE1.Seepage,advectionanddispersionpropertiesassignedtoeachcompositionlayerintheanalysis

Incoastallandfillsites,thedifferenceinthewaterlevelbetweentheinsideandoutsidelandfillsiteiscontrolled

onadailybasissothatitmaynotexceed2m(WaterfrontVitalizationandEnvironmentResearchCenter,2002).

Ontheotherhand,inthethreedimensionalcrosssectionshowninFig.5,acontrolledwaterlevelregulatedto2

misreproducedbytheboundaryconditions,thatis,afixedtotalheadof0and2mareassignedtotheupper

sidesoftheseaareaandwastelayer,respectively.Theboundaryedgesinthethreedimensionalcrosssectionof

thecoastallandfillsiteareassumedtobeundrained.Theseepage,advectionanddispersionpropertiesassignedto

eachcompositionlayerinthisanalysisareshownatTable1.ThesevaluesshowninTable1aretypicalonefor

heavymetalsandcompositionlayers(Kamonetal.,2001WaterfrontVitalizationandEnvironment

ResearchCenter,2002).Thisanalysisassumesthatmechanicalpropertiesofeachcompositionlayerarenot

considered.

Presently,inJapan,wastedischargewasteisburntonceatarefuseincineratorplant,andtheincineratedresidue

generatedfromtheincineratorplantismainlyusedtoreclaimlandatlandfillsites(Kamon&Inui,2002).

Therefore,thetypeofwastedumpedintherecentlyconstructedlandfillsiteshaschangedfromtheconventional

organicsubstancestoinorganicsubstancesthus,theheavymetalswhichmaybecontainedintheincinerated

residueareamongthemajorenvironmentalpollutants.Iftheleachateleakageoccursatalandfillsiteintothe

surroundingareas,theheavymetalsalsomayleakouttogetherwiththeleachateduetotheadvectiondispersion



phenomenon,asheavymetalsaresolubleinwater.Therefore,thisstudyassumesheavymetalsastoxicsubstances

thatmayleakoutfromcoastallandfillsites.Thisanalysisassumesthewastelayertobeacontaminationsource,

andtheconcentrationoftoxicsubstances(heavymetals)atthewastelayerisassignedthevalueof1astheinitial

condition.Theinitialrelativeconcentrationoftoxicsubstancesisinitializedto0inregionsoutsidethewaste

layer.

Asanenvironmentalconservationstandardforcoastallandfillsites(TheLandfillSystem&Technologies

ResearchAssociationofJapan,2004),theenvironmentalstandardvalues(seeTable2(b)and(c))for

waterqualityandbottomsedimentoftheseaareasnearlandfillsitesequal0.1timesthatoftheacceptable

standardvalues(seeTable2(a))forwastedisposedatlandfillsites.Therefore,theconcentrationoftoxic

substancesattheSPSPcutoffwallontheseaside(thatisthecrosssectiondelimitedbythebrokenlineatFig.

5)istargetedinthisanalysisasanimportantindexoftheenvironmentalfeasibilityofSPSPcutoffwalls.Inthis

analysis,theelapsedtimeduringwhichtheconcentrationoftoxicsubstancesreaches0.1ontheseasideofthe

SPSPcutoffwallisestimatedwhenthisoccurs,theSPSPcutoffwallaswellasthecoastallandfillsiteisdefined

ashavinglostitsenvironmentalfeasibility.

2.2.SP/JSMODELCONSIDERINGLOCALWATERLEAKAGEINJOINTSECTIONSIntheevaluationoftheenvironmentalfeasibility(containmenteffectofleachatecontainingtoxicsubstances)of

SPSPcutoffwallsatcoastallandfillsites,theequivalenthydraulicconductivityisgenerallyused(Waterfront

VitalizationandEnvironmentResearchCenter,2002).Thismethodinvolvescalculatingthehydraulic

conductivityofanSPSPcutoffwallequivalenttoauniformpermeablelayerofthickness50cm(seeFig.4)by

consideringthesteelpipesandjointsectionsthatconstitutetheSPSPcutoffwallasasinglebody.Becausethe

equivalenthydraulicconductivitycanbedirectlyverifiedwiththetechnicalstandardsforverticalandbottom

cutoffbarriersatlandfillsites,itisfrequentlyusedinthetechnicaldevelopmentoftheSPSPcutoffwall.

However,thevalueequivalenthydraulicconductivityistheaveragehydraulicconductivityofthejointsections,

whichhavehighpermeability,andthatofthesteelpipesections,whichareimpermeable.Therefore,an

evaluationusingtheequivalenthydraulicconductivitycannoteasilydetectthepositionorthetimeofleachate

leakage,thusmakingitdifficulttoestimatetheenvironmentalimpactoflocalleakagefromthejointsectionsof

theSPSPcutoffwall.Where,developmentofthesedetectionswillcontributestronglyfortheoptimizationof

maintenanceandmanagementinSPSPcutoffwall.



TABLE2.Environmentalconservationstandardsassociatedwithinlandandcoastallandfillsites



FIGURE7.GeneraldescriptionofULmodelandSP/JSmodelintheanalysis

Inthisstudy,anevaluationmethodthatcanexpressthelocalleakageatthejointsectionsofSPSPcutoffwallsis

discussed.TheevaluationmethodusingtheequivalenthydraulicconductivityisdefinedastheULmodel,and

theevaluationmethodthatconsidersthesteelpipeandjointsections,thatis,thelocalleachateleakage,isdefined

astheSPJSmodel.Figure7showsageneraldescriptionoftheULmodelandSP/JSmodel.IntheUL

model(showninFig.7(a)),equivalenthydraulicconductivitiesof2.0106,1.0106,1.0107and1.010

8cm/swereassignedtotheentireSPSPcutoffwall.IntheSP/JSmodel(seeFig.7(b)),thejointsectionswere

placedat0.25mintervalsforsteelpipesofdiameter1m,whichrepresentsthestandardsizesoftheSPSPshown

inFig.2.Furthermore,hydraulicconductivitieswereassignedtoeachsteelpipeandjointsectionintheSP/JS

modelsuchthattheentirehydraulicconductivityoftheSPSPcutoffwallequalstheequivalenthydraulic

conductivityassignedintheULmodel,thatis,hydraulicconductivitiesof2.5106,1.3106,1.3107and

1.3108cm/swereassignedtothejointsections,assumingthatthehydraulicconductivityofsteelpipeis

infinitelysmall.Table1showstheseepage,advectionanddispersionpropertiesassignedtoeachcomposition

layerinboththemodels.

3.Resultsanddiscussion



3.1.ENVIRONMENTALFEASIBILITYOFSPSPCUTOFFWALLCONSIDERINGLOCALWATERLEAKAGE

Figure8showstheconcentrationflux(thematerialquantitypassingthroughaunitareainunittime)oftoxic

substancesleakingfromtheSPSPcutoffwallontheseaside.ThefluxesintheuniformlayeroftheULmodel

andineachsteelpipeandjointsectionoftheSP/JSmodelareplottedinFig.8.Therelationshipbetweenthe

elapsedtimeandthehighestconcentrationoftoxicsubstancesleakedfromtheSPSPcutoffwallontheseaside

forboththemodelsisshowninFig.9.Figure10illustratesthedistributionoftheconcentrationoftoxic

substancesleakingoutfromthewastelayer,whichisthecontaminatedsource,forboththemodels.Figure

10expressesthedistributionoftheconcentrationontheseasideoftheSPSPcutoffwallinordertofacilitatethe

comparisonofboththemodelswithregardtotheleakageofthetoxicsubstancetothesurroundingsofthecoastal

landfillsite.

FIGURE8.ConcentrationfluxoftoxicsubstancesleakingfromSPSPcutoffwallonseasidewithelapsedtimeforboth

models

IntheSP/JSmodel,theconcentrationfluxoftoxicsubstancesleakedontotheseasideoftheSPSPcutoffwall,

particularlyfromthejointsections,isincreasedascomparedtothatoftheULmodel(seeFig.8).TheSP/JS

modelcanquantitativelyexpresstheconcentrationoftoxicsubstancesatthejointsectionsoftheSPSPcutoff

wall,wherethehydraulicconductivityishigherthanthatinthesteelpipe.IntheULmodel,asshowninFig.

10,theleachateleaksuniformlyfromtheSPSPcutoffwallontotheseaside,andthisleakagetendstouniformly

increasewithtime.IntheSP/JSmodel,itbeingdifferentfromtheULmodel,theleachateleakslocallyfromthe

jointsectionsontotheseasideoftheSPSPcutoffwall,andthisleakageincreaseslocallywithtimeatthejoint

sections(seeFig.10).Consequently,theincreaseintheconcentrationoftoxicsubstancesleakedfromtheSPSP

cutoffwallontotheseasideisfoundtooccurearlierintheSP/JSmodelthanintheULmodel,asshowninFig.



9.

FIGURE9.RelationshipbetweenelapsedtimeandthehighestconcentrationoftoxicsubstancesleakedfromSPSPcutoff

wallonseasideforbothmodels

Forexample,70and110years,respectively,arerequiredintheSP/JSmodel(thehydraulicconductivityofthe

entireSPSPcutoffwallis1.0108cm/s)andtheULmodelfortheconcentrationoftoxicsubstancesinthe

SPSPcutoffwallontheseasidetoreachC=0.1,whichisassumedastheassessmentindex.Intheotheranalyzed

conditionsunderwhichthehydraulicconductivityoftheentireSPSPcutoffwallisequivalentinbothmodels,the

leakageofleachateisconfirmedtooccurearlierintheSP/JSmodelthanintheULmodelduetoeffectofthe

localleakageofleachate(seeFig.11).Thistendencybecomesmoreremarkablewithincreaseinthehydraulic

conductivityoftheentireSPSPcutoffwall(seeFig.12).

Thus,asmentionedabove,thereproductionofthelocalleakageofleachategeneratedatthejointsectionsof

SPSPcutoffwallsispossiblebyusingtheSP/JSmodelfortheevaluationoftheenvironmentalfeasibilityof

SPSPcutoffwallsatcoastallandfillsites.Furthermore,theSP/JSmodelindicatesthattoxicsubstancesin

concentrationsexceedingtheenvironmentalstandardvaluesareleakedoutofcoastallandfillsitesearlierthanthat

estimatedusingtheULmodel(seeFig.9).UsingtheULmodel,thelocalleakageofleachatecontainingtoxic

substancesfromtheSPSPcutoffwallcannotbereproduced,althoughthetotalquantityofthetoxicsubstances

leakedfromtheSPSPcutoffwallcanbeestimated.Thisprovidesasafersideestimateoftheenvironmental

feasibilityfromtheviewpointofthetimetakenfortheleakageoftoxicsubstances.Inaddition,byusingtheUL

model,itisdifficulttoquantitativelydetectthegenerationpositionintheSPSPcutoffwallwheretheleachate

containingtoxicsubstancesareleaked.Anappropriateestimationintermsofbothpositionandtimeatwhichthe



lossofenvironmentalfeasibilityoccursisimportantinordertocontrolandmaintainalongtermSPSPcutoff

wallatcoastallandfillsites.Basedontheabovementionedpoints,theenvironmentalfeasibilityofSPSPcutoff

wallsmustbeverifiedbyusingtheSP/JSmodel.

FIGURE10.Distributionofconcentrationoftoxicsubstancesleakingoutfromwastelayerforbothmodels

3.2.ENVIRONMENTALFEASIBILITYOFSPSPCUTOFFWALLCONSIDERINGJOINTSECTIONS

VarioustypesofjointsareadoptedforthejointsectionsoftheSPSPcutoffwalls,asshowninFig.2.Thetypes

ofjointsforwhichthehydraulicperformancehasbeenreportedexperimentallyarethePTjointsinwhichthe

packingmortarisfilledinthejointspace,theimprovedPTjointinwhicharubberboardisinstalledwiththe

mortarfillinginthejointspaceandtheHHjointforHjointedSPSPinwhichawaterswellingsheetisapplied

inthejointspaces(Okietal.,2003Inazumietal.,2005,2006Kimuraetal.,2007).Basedonpast

reports,theSPSPswiththePTjoint,improvedPTjointandHHjointexhibitequivalenthydraulic



conductivitylevelsof1106,1108and1109cm/s,respectively,underspecificexperimentalconditionsunder

whichthedifferencebetweenthewaterlevelsinsideandoutsidethelandfillsiteislessthan5m(Okietal.,

2003Inazumietal.,2005,2006).However,thereportedhydraulicperformancesoftheSPSPcutoffwalls

withthejointsectionshasbeenbasedontheequivalenthydraulicconductivitiesobtainedfromexperimental

studies.

FIGURE11.RequiredtimeforconcentrationoftoxicsubstancesinSPSPcutoffwallonseasidetoreachC=0.1with

equivalenthydraulicconductivityofSPSPcutoffwall

FIGURE12.Requiredtimeratioofbothmodels,forconcentrationoftoxicsubstancesinSPSPcutoffwallonseasideto



reachC=0.1,withequivalenthydraulicconductivityofSPSPcutoffwall

Inthisstudy,thereportedequivalenthydraulicconductivitiesofSPSPcutoffwallsareconvertedtoindividual

hydraulicconductivitiesinthesteelpipeandjointsections.



FIGURE13.DimensionandhydraulicconductivityofSPSPcutoffwallwitheachjointtypeandoutlineofSP/JSmodelfor

CaseItoCaseIV

Furthermore,theenvironmentalfeasibilitiesofSPSPcutoffwallswithvariousjointstypesareevaluatedby

applyingeachconvertedhydraulicconductivityintheSP/JSmodel.Figure13showstheequivalenthydraulic

conductivitiesofSPSPcutoffwallswithvariousjointstypes,thedimensionofeachjointtypeaswellassteel

pipeandthehydraulicconductivityofeachjointtype.Intheevaluationoftheenvironmentalfeasibilitieson

SPSPcutoffwallsconsideringvariousjointgeometriesandperformancelevels,theSPSPcutoffwallswiththe

followingfourjointtypesareappliedtotheSP/JSmodel.

CaseI:SPSPcutoffwallwiththePTjoint

CaseII:SPSPcutoffwallwiththeimprovedPTjoint

CaseIII:HjointedSPSPcutoffwallwiththeimprovedPTjoint

CaseIV:HjointedSPSPcutoffwallwiththeHHjoint

Figure13showsalsotheoutlineoftheSP/JSmodelforCaseItoCaseIV.Jointsectionsofwidth0.25mand

steelpipesofdiameter1mwereusedinCaseIandCaseII,whereasjointsectionsofwidths0.25mand0.5m

wereusedinCaseIIIandCaseIV,respectively,alongwithHjointedsteelpipesofdiameter2.25m(Okietal.,



2003Inazumietal.,2005,2006).Table1showstheseepage,advectionanddispersionpropertiesassigned

toeachcompositionlayer

Theassumedhydraulicconductivitiesofthejointsectionswere1.3106cm/sinCaseI,1.3108cm/sinCaseII

andCaseIIIand1.8109cm/sinCaseIV.

Figure14showsthetotalquantitiesoftoxicsubstancesleakedfromtheSPSPcutoffwallontotheseasidewith

respecttotheelapsedtimeforCaseItoCaseIV.Therelationshipsbetweentheelapsedtimeandthehighest

concentrationoftoxicsubstancesleakedfromtheSPSPcutoffwallontotheseasideforCaseItoCaseIVare

showninFig.15.Figure16showsthedistributionoftheconcentrationoftoxicsubstancesleakingoutfromthe

wastelayer,thatis,thecontaminationsource,inCaseItoCaseIV.ThisdistributioninFig.16isexpressed

fromtheseasideoftheSPSPcutoffwallinordertofacilitateacomparisonamongCaseItoCaseIVwithregard

totheleakageofthetoxicsubstancetooutsidethecoastallandfill.

ThetimesrequiredfortheconcentrationlevelsontheseasidetoexceedC=0.1werelessthan1yearand70years

forCaseIandtheCaseII,respectively(seeFig.15).InCaseIIIandCaseIV,theleakageoftoxicsubstancesin

excessofenvironmentalstandardvalue(C=0.1)wasnotconfirmed,evenfordurationsupto140years.InCaseI

andCaseII,thehydraulicconductivitiesofthejointsectionsaredifferent,althoughthearrangementintervalsof

thejointsectionsarethesamethusithasbeenproventhatlowhydraulicconductivityjointsectionsinSPSP

cutoffwallssignificantlycontributetowardincreasingtheleachatecontainmenteffect.Inaddition,thesparser

arrangementofjointsectionsrepresentedinCaseIIIreducesthetotalquantityoftoxicsubstancesleakedfromthe

SPSPcutoffwallontotheseasidetohalfthatinCaseII(seeFig.14).Consequently,theleachateleakedtothe

outsideofthecoastallandfillsitesisreducedbythelowhydraulicconductivityaswellasthesparserarrangement

ofjointsectionsintheSPSPcutoffwall,thus,significantlyimprovingtheleachatecontainmenteffect.

TheHjointedSPSPcutoffwallwithHHjoints(CaseIV)mostefficientlyachieveslowhydraulicconductivity

withasparserarrangementofjointsections.TheleakageofleachatesinCaseIVcanbetracedtothelower

reachesofthecutoffwall,occurringviatheclaydepositlayer,whichisoneofthebottomcutoffbarriersandis

furtherawaythanotherpathwayssuchasleakagedirectlythroughthecutoffwall(seeFig.16).Thus,theH

jointedSPSPcutoffwallwiththeHHjointsufficientlycontributestotheleachatecontainmenteffectofvertical

cutoffbarrieratcoastallandfillsites.



FIGURE14.TotalquantitiesoftoxicsubstancesleakedfromSPSPcutoffwallontoseasidewithrespecttotheelapsedtime

forCaseItoCaseIV

FIGURE15.RelationshipsbetweenelapsedtimeandthehighestconcentrationoftoxicsubstancesleakedfromSPSPcutoff

wallontoseasideforCaseItoCaseIV

Inthissection,itwasclarifiedthattechnologiesthatlowerthehydraulicconductivitiesofjointsectionsinSPSP

cutoffwallsandalsofacilitatetheuseofsparserarrangementscontributesignificantlytoincreasingthe

environmentalfeasibilitiesofSPSPcutoffwallsatlandfillsites.Further,theextentoftheenvironmental

feasibilityofHjointedSPSPcutoffwallswiththeHHjointsamongthepresenttechnicaldevelopmentsinSPSP



cutoffwallswasshown.



FIGURE16.DistributionofconcentrationoftoxicsubstancesleakingoutfromwastelayerinCaseItoCaseIV

4.Conclusions

Anevaluationmethodthatcanexpressthelocalleakageofleachatefromjointsectionsinsteelpipesheetpile

(SPSP)cutoffwallsisdiscussed,inthisstudy.Inparticular,theevaluationofenvironmentalfeasibility

(containmentofleachatescontainingtoxicsubstances)consideringathreedimensionalarrangementandhydraulic

conductivitydistributionofthejointsectionsintheSPSPcutoffwalliscomparedwithanevaluationthat

generallyusestheequivalenthydraulicconductivity.

EvaluationsoftheenvironmentalfeasibilitiesoftheSPSPcutoffwallswithjointsectionsthathaveahigher

hydraulicconductivitythanthatofthesteelpipemusttakeintoaccountthelocalleakageofleachatescontaining

toxicsubstancesfromthejointsectionthiswaspossibleusingtheSP/JSmodel.Duetothelocalleakageintothe

surroundingsofcoastallandfillsfromjointsections,contaminationinexcessoftheenvironmentalstandardvalues

wasconfirmedtooccurearlierthanthatpredictedbytheULmodel,whichisthecurrentstandardevaluation

method.

ItwasclarifiedthattechnologiesthatlowerthehydraulicconductivitiesofjointsectionsinSPSPcutoffwallsand

alsofacilitatetheuseofsparserarrangementscontributesignificantlytoincreasingtheenvironmentalfeasibilities

ofSPSPcutoffwallsatlandfillsites.Further,theextentoftheenvironmentalfeasibilityofHjointedSPSP

cutoffwallswiththeHHjointsamongthepresenttechnicaldevelopmentsinSPSPcutoffwallswasshown.

hydraulic conductivity of steel pipe sheet pile cutoff walls at coastal waste landfill sites _...

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