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2024年6月1日发(作者：)

UseofaLineofPilestoPreventDamages

InducedbyTunnelExcavation

EmilioBilotta

1

andGianpieroRusso

2

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Abstract:Buildingsfoundedinproximitytoshallowtunnelsunderconstructionmaybedamagedbythegrounddisplacements

amatterofconcernfordesign,andavarietyofprotectiveinterventionsarecurrentlyadoptedtopreventsuch

hese,paper,theeffectivenessofasimplerowofpilesis

computedbymeansofthree-dimensional(3D)finite-element(FE)analyses,thusallowingtheinvestigationoftherelationshipbetween

performanceandsomesimplegeometricalparameters,ultsofcentrifugetestsarereported

entialdamagehasbeenquantifiedinthiswork,takingintoaccountboththesettlementprofileand

ownthatalthoughthesettlementreductionissignificantonly

forverysmallspacing(s¼2–3pilediameters),evenlargelyspacedpiles(s¼5–6pilediameters)areusefultopreventdamagetobuildings

:10.1061/(ASCE)GT.1943-5606.0000426.©2011American

SocietyofCivilEngineers.

CEDatabasesubjectheadings:Tunnels;Piles;Excavation;Settlement;Damage;Protectivestructures.

Authorkeywords:Tunnels;Piles;Excavation;Settlement;Damage;Protectivestructures.

Introduction

Thebehaviorofpilesduringtheexcavationofshallowtunnelshas

concern

istheinteractionbetweentunnelsanddeepfoundationsandthe

needtoavoiddetrimentaleffectsonadjacentpiledbuildingsor

lresearchershaveworkedinthisfieldonboth

hem,Chenetal.

(1999)andLoganathanetal.(2001)comparedtheresultsof

simplifiedboundary-element(BE),finite-element(FE),andfinite-

difference(FD)analysesofsingle-pileandpile-groupresponseto

ghlightedtheinfluenceofseveral

factors,suchaspilelengthandlocation,andshowedthatwhen

thepiletipislocatedbelowthetunnel,thepile-headsettlement

dometal.(2005)extendedtheconclusionsof

thepreviousworkstopiledrafts,alsoshowingthattheresponse

ofpiledraftandpilegroupisalmostidenticalwhenthepile-

slendernessratioishigh(L=d¼25).

Three-dimensional(3D)numericalmodelingbyLeeandNg

(2005)evidencedazoneofinfluenceoftheexcavationonthepile,

roughlyfromonetunneldiameteraheadtoonediameterbehindthe

tunnelexcavationface,wherethepilesettlementislargerthan

thegroundsurfacesettlementbecauseoftheyieldingofsoilaround

stresultisconsistentwiththeexperimental

AssistantProfessor,DepartmentofHydraulic,GeotechnicalandEnvir-

onmentalEngineering,liFedericoII,ViaClaudio21,80125

Napoli,Italy.

2

Ph.D.,AssociateProfessor,DepartmentofHydraulic,Geotechnical

andEnvironmentalEngineering,liFedericoII(Italy),Via

Claudio21,80125Napoli,Italy.

nuscriptwassubmittedonOctober14,2009;approvedon

August5,2010;publishedonlineonAugust11,sionperiod

openuntilAugust1,2011;separatediscussionsmustbesubmittedfor

perispartoftheJournalofGeotechnical

andGeoenvironmentalEngineering,Vol.137,No.3,March1,2011.

©ASCE,ISSN1090-0241/2011/3-254–262/$25.00.

1

findingsfromplane-straincentrifugetestsreportedbyJacobszetal.

(2004).Also,centrifugetestsperformedbyLoganathanetal.

(2000)showedagoodagreementwiththenumericalresultsof

LeeandNg(2005)intermsofbothsubsurfacesettlementsandpile

internalforces,,

whentheexcavationfrontisaboutthreetunneldiametersbeyond

thepilesection).CentrifugetestsbyMcNamaraetal.(2003)and

LeeandChiang(2007)onloadedpileshighlightedthatthehigher

theworkingloadbeforetunneling,thehigherthesettlementof

thepileafter.

Morerecently,YooandKim(2008)used3Dnumericalanalyses

ofopen-facetunnelingclosetoapile-supportedbuildingto

showthatreducingthetunnelfacelosswillminimizenotonly

thebuildingsettlementbutalsoitstilting.

Theinfluenceofthelocationofpiletoerelativetothetunnel

wasalsoshownforembeddeddiaphragmwallsbyBilotta

(2004,2008)andBilottaandStallebrass(2009)inbothcentrifuge

eproblemwasstudied

with1gphysicalmodelingbyLeeandBasset(2006)andLee

andYoo(2006).

Incommonpractice,pileshavebeensometimespurposely

installedbeforetunnelingtoprotectexistingfoundationsfrom

,thelevelofdamagethatcanbe

sufferedbyabuildingfoundedclosetoshallowtunnelsunder

construction,suchasthosecommonlyexcavatedwithtunnelboring

machines(TBMs)forurbanundergroundrailways,isoneofthe

keyquestionsofthedesignstage.

Applicationsofalineofpiles,interposedbetweenthetunnelto

beexcavatedandtheexistingbuildingtobeprotected,havebeen

,

Gensetal.2006;DiMarianoetal.2007).

Oteoetal.(2007)collectedanumberofcasehistoriesinwhich

theefficiencyofdoublerowsofjet-groutingcolumnswithdifferent

finetheefficiencyastheratio

betweengreenfieldsettlementandthesettlementwiththeprotect-

ingmeasure,reportingexperimentalresultswithacoefficient

254/JOURNALOFGEOTECHNICALANDGEOENVIRONMENTALENGINEERING©ASCE/MARCH2011

J. Geotech. Geoenviron. Eng. 2011.137:254-262.

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rmore,theauthorsfound

thatthelowerthestiffnessoftheundisturbedsoilthehigherthe

efficiency.

Inthispaper,theefficiencyofasinglerowofunloadedpilesis

computedbymeansof3DFEanalyses,investigatingthepossibility

ofoptimizingthedesignofthelinebyvaryingthespacingbetween

eoftheadopted3Dmesh,asimpletwo-dimensional

(2D)excavationschemewasusedtosimulatethetunnelconstruc-

tion,allowingcomparisonwiththeresultsofcentrifugetests

(Bilottaetal.2006a)oiceprevented

thedevelopmentofdisplacementpatternssuchasthoseevidenced

byYooandKim(2008),characterizedbythetiltingofpiledbuild-

eformation

patternisunrealisticforatunnelexcavatedbyTBM,wheretheface

lossisgenerallynegligible.

Thechoiceofgreenfieldconditionsasareferenceforevaluat-

ingtheefficiencyofthepilesisjustifiedbythefactthatmany

methodstodefinethelevelofdamageonthestructuresarebased

tance,anestablishedprocedurefor

assessingthedamageonmasonrybuildingshasbeenproposed

byBurlandetal.(2003).Suchaprocedurehasbeenwidelyused

duringthedesignoftheJubileeLineextensioninLondon

(Burlandetal.2001).BasedontheworksofBurlandandWroth

(1974)andBurlandetal.(1977)onsettlementsofbuildingsand

associateddamagesandontheworkbyBoscardinandCording

(1989)ontheresponseofbuildingstoexcavation-inducedsettle-

ments,theprocedurerelatesthelevelofdamagesufferedbya

masonrybuildingtothegreenfieldprofileofsettlementsinduced

bytunneling.

Theinfluenceofthepilespacingonthereductionofthelevelof

damageinducedtoamasonrybuildingwithashallowfoundationis

alsoshowninthispaper.

NumericalModel

Theresultsofasetofanalysesona3DFEmodelofalineofpiles

onthesideofashallowcirculartunnelbeingexcavatedin

neliscir-

cular,withdiameterD¼8masanaveragevalueofthosetypical

forundergroundrailways;thetunnelaxisissetatthedepth

z

o

¼Cþ0:5D¼,covertodiameterratioC=D¼

,just

beyondtheinflectionpoint,wherethegreenfieldsettlementtrough

ometrywas

thoughttoberepresentativeofatypicalcaseforusinganefficient

verticalbarriertomitigatethegroundmovementsinducedbytun-

neling,basedontheresultsofapreviousplane-strainparametric

analysis(Bilottaetal.2006b).Thatworkshowedthatforcircular

tunnelswithC=D¼1–2,averticaldiaphragmwalllocatedwithin

onetunneldiameterawayfromthetunnelsideshouldbeatleastas

deepastheinvertleveltobeeffectiveinreducinggroundmove-

ments,andthattheefficiencyofthewalldoesnotimprovenotice-

eofthespacing

betweenpiles,theefficiencyofalineofpilesisexpectedtobe

ore,thepilesweredeepened

about0:5Dbelowthetunnelinvert(L≅Cþ1:5D)toaccountfor

parison,asetofanalyseswasalso

performedwithshorterpiles(L≅Cþ0:5D).Thepile-soilrelative

stiffnesswasvariedbychangingboththepileandsoilstiffness.

Thenumericalanalyseshavebeenperformedbymeansofthe

FEcodePlaxis3DTunnel(BrinkgreveandBroere2004)thathas

beendevelopedspecificallyfortheanalysisofboundary-value

-

gramallowsa3DFEmeshtobegeneratedbasedonarepetitive

hofsuchasection,intheplane

transversetothetunnellongitudinalaxis,was80mwideand30m

frontviewandelevation(L≅Cþ1:5D)

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rametersforHardeningSoil

Parameter

γ

E

50;ref

(forp

ref

¼100kPa)

E

ur;ref

(forp

ref

¼100kPa)

E

oed;ref

(forp

ref

¼100kPa)

Cohesionc

Frictionangleϕ

Dilatancyangleψ

Poissonratioν

ur

Powerm

Tensilestrength

Failureratioq

failure

=q

asymptote

Value

17.5

8to25

2:8·E

50;ref

E

50;ref

0.001

(20°to30°)

0

0.2

1

0

0.9

kN=m

3

MPa

MPa

MPa

kPa

°

°

—

—

kPa

—

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extrudedforawidthof3malongthethirdaxisforming13adjacent

slicesofapproximately13,rvertical

boundariesofthemeshwerefixedinthehorizontaldirectionand

leftfreetosettle;thebottomwasfullyfixed,inhibitingbothhori-

undwatertablewassetat

thegroundlevel,andtheinitialeffectivestressfieldwasderived

fromthesoilfrictionangleϕ

0

byassuminganearthpressureco-

efficientK

0

¼1Àsinϕ.AviewofthemeshisshowninFig.1.

Thecomputationwasperformedusingeffectivestressesandthe

soilwasmodeledbytheHardeningSoilmodel,anonlinearelastic-

plasticconstitutivelawwithvolumetricanddeviatorichardening,

implementedinthecode(Schanzetal.1999).Thesetofconstit-

utiveparametersassumedintheanalysesisshowninTable1.

Thetunnelwasmodeledasacircularunlinedcavity,supported

withaloaddistributionequaltothestressesexchangedonthe

avationwasthensimulatedin

severalstepsassociatedwithdifferentpercentagesofstressreduc-

greenfieldanalysisallowed

thecomputationofthesettlementtroughsatdifferentstressreduc-

tionlevels.

Thepilesweremodeledasstructuralelementswiththesame

aceelementswerealsointerposedbetween

thestructuresandthesoil,becausetheyallowthesizeofthesoil

elementstobeincreasedaroundthestructurecomparedtothe

modelwithoutinterfaceswithnosignificantlossintheaccuracy

aviorofarealinterfacestrongly

dependsontheconstructionprocessofthepile,andtheinterface

heless,

asinthisstudythepileswereconsideredaswished-in-place,this

issuewasconsistentlyneglectedandthesamestiffnessandstrength

ofthesurroundingsoilwereattributedtotheinterfaceelements.

Theinfluenceofthepile-soilinterfaceontheefficiencyoftheline

ofpilesinmitigatinggroundmovementsisbeyondthescopeofthis

work,butitwasdiscussedforthelimitedcaseofacontinuouswall

ofpilesbyBilotta(2008)onthebasisofbothcentrifugetestsand

FEanalyses.

Thestructuralelementmodelingthepilewasanelasticplateof

rectangularcrosssectionwithgivenflexuralandaxialstiffness

perunitwidth(EIandEA,respectively),asshowninTable2:a

relativestiffnessbetweenthesoilandstructurewasdefinedas

EI=E

50;ref

D

3

,whereE

50;ref

isareferencestiffnessmodulusfor

thehardeningsoilmodel(Schanzetal.1999).Eachpilehadafinite

thesliceshadawidthb¼0:25m,exceptforthefrontandrear

sliceswhosewidthwassettob¼0:lyseswerecar-

riedoutwithrowsofpilesatdifferentspacings:fivedifferentvalues

oftheratios=bweremodeled(s=b=2,3,4,6,and12).A3-m-wide

,s=b¼1,esofthese

configurationsareshowninFig.2.

uralElementCharacteristics

L(m)

Piles

Diaphragmwall

From11.2to19.2

b(m)

0.25

3

EI(kNm

2

=m)

From5:90Eþ4to3:43Eþ6

EA(kN=m)

From1:43Eþ7to5:46Eþ7

ν

0.25

s=b

2;3;4;6;12

—

urationsofstructuralelements

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isonof(a)settlementtroughand(b)surfacehorizontaldisplacementsindifferentconfigurations(L≅Cþ1:5D)at

V

0

¼1%ÀE

50;ref

¼25MPa

GroundandStructureDisplacements

SurfaceSettlementsandGroundHorizontal

Displacements

Settlementsandhorizontaldisplacementswerecomputedatthe

surfaceinthenumericalmodelwithpilesandcomparedtothe

vesshowninFig.3

(L≅Cþ1:5D)wereplottedforareferencesetofsoiland

platestiffness(E

50;ref

¼25MPa,EA¼1:43×10

7

kN=mand

EI¼5:90×10

4

kNm

2

=m).Differentcurvesarecomparedin

thefigurefordifferentvaluesofs=curvesrefertothe

sameamountofvolumeloss,V

0

¼1%.AGaussianprofile

(Peck1969)computedbyassuminganinflectionpointi¼

0:5Ãz

o

(K¼0:5)isalsoshowninFig.3(a)forcomparisonwith

ureshowsthattheset-

tlements[Fig.3(a)]andthehorizontaldisplacements[Fig.3(b)]at

therightsideofthelineofpilesdecreasedascomparedtothe

ductionisadecreasingfunctionofthe

pilespacing,thehigherreductionbeingobservedforthecontinu-

ousdiaphragmwall(s=b¼1).Fig.3(a)alsoshowstheincreaseof

settlementabovethetunnelcenterlineinundrainedconditions,

sincethepredictionsarecomparedatthesamevolumeloss.

Thesurfacesettlementofthealignmentinthelongitudinaldirec-

tionzatx¼esgenerallysettlelessthan

thesurroundingground:thesoilsettlementbetweenthepiles

r,thegroupeffect

ofthepileinthelineisthatofgloballyreducingtheaverage

settlement.

HorizontalDisplacementsofthePilesandthe

DiaphragmWall

Thehorizontaldisplacementsofthelineofpilesonthefrontplane

ofthemodel(z¼3)areshowninFig.5(L≅Cþ1:5D)atthe

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mentsalongthelineofpiles(L≅Cþ1:5D)inlongitudinaldirectionandgreenfield,atV

0

¼1%ÀE

50;ref

¼25MPa

ntaldisplacementsonthefrontplane(z¼3m),forseveralconfigurations(L≅Cþ1:5D)atV

0

¼1%ÀE

50;ref

¼25MPa

samevolumeloss(V

0

¼1%)foralltheconfigurationsexcept

s=b¼12ands=b¼4,wherenopileswereonthefrontslice.

Thepresenceofpilesaltersthegreenfielddeformationpatterns

ngreenfieldconditions,thesoilatthe

depthofthetunnelisattractedtowardthecavity,butthepiles,

whicharefoundedbelowthetunnelinvert,reducesuchapattern

therhand,theexcavationcausesthehori-

zontaleffectivestressestoincreaseatmiddepthbetweenthetunnel

singreenfieldconditions,soilarch-

ingpermitsagradualadjustmentofthestressesaroundthetunnel,

anunbalancedthrustarisesonthepiles,loadingthemoutwardand

producinghorizontaldisplacementsoppositetothegreenfieldcon-

ally,nearthesurface,thehorizontaldisplacements

areinallcasesdirectedtowardthetunnel,theirmagnitudedecreas-

ingasthepilespacingdecreases.

theGeotechnicalEngineeringResearchCenterofCityUniversity

London(Bilotta2004;Bilottaetal.2006a).

of

eighttestswereconsidered,whichcanbedividedintothreegroups.

Foreachgroup,

addition,Group1comprisesatestonamodelaluminumdia-

phragmwallwiththetipreachingapproximatelythetunnelaxis

(L≅Cþ0:5D);Group2acomprisesatestonadiaphragmwall

esoftheBenchmarkTests

Group

1

2a

2b

Test

EB2

EB3

EB6

EB13

BB1

BB2

BB3

BB4

C=D

0.9

1

1

1

1

3.1

6.2

12.5

s=bL(mm)[m]b(mm)[m]d(mm)[m]

50[8]

50

75

75

75

[8]

[12]

[12]

[12]

ExperimentalBenchmark

Thenumericalanalyseswerecomparedwiththeexperimental

resultsofaseriesofcentrifugetestsperformedinstiffclayat

Greenfield

70[11.2]0.8[0.136]

Greenfield

120[19.2]0.8[0.136]

120[19.2]1.6[0.316]

120[19.2]1.6[0.316]

120[19.2]1.6[0.316]

Greenfield

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foundedbelowthetunnelinvert(L≅Cþ1:5D);andGroup2b

comprisesthreetestsonlinesofaluminumpilesofthesamelength

ofgroup2a,butwithdifferentspacing.

Allthetestswereperformedat160g,allowingthemodelsizeto

uesshown

inthetablerefertothemodelscale(inmm)andthecorresponding

valuesattheprototypescalearealsoshowninitalics(inm).Inthe

table,thesymbolbrepresentseitherthewidthofthediaphragm

elreinforcingelements

(wallorpiles)weremadeofaluminum,butTable3indicatesthe

equivalentthicknessoftheprototypeshadtheybeenconstructedof

reinforcedconcrete,accordingtothedifferentYoung’smoduliof

thetwomaterials.

EffectivenessoftheProtectingMeasure

Theeffectivenessofaverticalstructuralelementforreducingthe

settlementsinducedbytunnelingcanbeexpressedbyanefficiency

parameterasfollows:

η¼ðS

ref

ÀS

bp

Þ=S

ref

ð1Þ

whereS

bp

=settlementofthegroundsurfaceimmediatelybeyond

theheadofpiles;andS

ref

=surfacesettlementatthesamelocation

inthegreenfield.

Intheexperiments,thedisplacementsoftargetslocatedatthe

frontfaceofthemodelweremeasuredusinganimage-based

deformationanalysissystem(Tayloretal.1998).Thusthevalue

ofS

bp

wascalculatedbyextrapolatingthetrendofmeasurements

behindthepileorwalltothereferenceposition.

Inthenumericalanalyses,profilesofS

bp

,suchasthoseshownin

Fig.4,werecalculatedasfollows:asthedisplacementvarieswith

thelongitudinalabscissaz,themaximumsettlementoftheground

betweenpileswasusedtocomputetheefficiency.

InFig.6,suchcurvesofefficiencyareplottedforV

0

¼1%;the

twobandshatchedinthebackgroundrepresenttheenvelopeofthe

sameresultsforV

0

rangingbetween0.5%and2.5%,whicharenot

.6alsoshowstheresults

ofthecentrifugetestsforV

0

=1.35and5%(pairsofpointsatthe

sames=b).ResultsforlowervaluesofV

0

werenotreportedbecause

theywerejudgedunreliableowingtotheaccuracyofthemeasuring

device.

Theexperimentalresultsshowanefficiencyslightlylowerthan

enumerical

andexperimentalresultsshowthevolumelossinfluenceonthe

iciencyofthelonger

piles(L≅Cþ1:5D)appearshighandrelativelyconstantforsmall

valuesofspacing:averagingabout0.9fors=b<2accordingtothe

numericalanalyses(relativestiffnessEI=E

50;ref

D

3

¼0:0046,value

similartotheexperiments).Ontheotherhand,itisverylowfor

s=b>6:er,forthelongerpiles,in

boththetestsandFEanalyses,itappearsthatfors=b<4thehigher

theV

0

thehighertheefficiency;theoppositeistruefors=b>4.

ThetriangularmarkersinFig.6indicatetheefficiencycalcu-

latedat1.35%and5%forthetestEB3wherethediaphragmwall

(s=b¼1)wasshorterthaninthetestEB13(circularmarkersatthe

sames=b¼1)andapproximatelyreachedthetunnelaxisdepth

(withL≅Cþ0:5D).Theefficiencyoftheshorterdiaphragmwall

islowerthanthelongerwall(L≅Cþ1:5D);thisisconsistent

withtheresultsofthecentrifugetestscarriedoutbyLee

andChiang(2007)onunloadedpileshavingdepthratios

L=ðCþ0:5DÞ≥teroffact,fromtheexperimentalpoint

ofviewtheefficiencyofadiaphragmwallwithL¼Cþ0:5Dis

comparabletothatofalineofpilesoflengthL¼Cþ1:5Dand

spacings=b¼rthnotingthatthenumericalpredictions

showhigherefficiencyfors=b<3thanfortheexperimentalfind-

ing,beingηfors=b¼1ashighas0.6comparedtothecorrespond-

ingvalueofabout0.3measuredintestEB3.

InFig.6,thesmallandalmostnegligibleinfluenceofthe

relativestiffnessisalsoshown(continuousthinlinesforthemore

,EI=E

50;ref

D

3

¼0:0046,dashedthicklinesfor

,EI=E

50;ref

D

3

¼0:27).

Thegeneralagreementbetweentheefficiencycomputedbythe

numericalanalysesandthatobtainedbythecentrifugetestson

modelsofsimilargeometry(pilelengthandtunneldiameterand

cover)andsoilconditions(undrainedexcavationinstiffclay)is

goodats=b≥ifferencesariseats=b¼cen-

trifugemodelswerepreparedaccordingtothesameprocedure

(Bilottaetal.2006a)withtheonlyexceptionbeingthemodelswith

s=b¼1(Bilotta2004).Althoughinallthecasestheclaysamples

wereobtainedbyconsolidationat1gofakaolinslurry,thepiles

werepushedinsidetheconsolidatedclay,whilethediaphragm

numericalanalysesdidnotmodelsuchdifferences.

DamageAssessment

Thenumericalresultsandtheexperimentaldatadiscussedinthe

previoussectionsshowthatalineofpilescanbeusedforlimiting

thedamageoccurringtobuildingsfoundedinthehoggingpart

iciencyofsuchlinesinreducing

settlements,asexpressedbyEq.(1),mayneedtobereconsidered

inthelightofthelevelofdamageinducedtobuildings.

ThedeflectionratioΔ=L(BurlandandWroth1974)between

theedgesofthefoundationlineandtheaveragehorizontalground

strainε

h

mer

canberelatedtothestrainsarisingfrombendingandshearand

computedaccordingtothetheoryofTimoshenko(1957)foralin-

earelasticbeam;thelatterisdetrimentalwhenthebuildingfoun-

hoggingpartofthesettlementtroughwasthereforetakeninto

account.

Asthelineofpileswaslocatedatd¼8mfromthetunnelaxis

(x¼0),onlythepartofgroundsurfacebetweenx¼dandx¼dþ

L

hog

tanceL

hog

hasbeenassumedtobe

hvalueofL

hog

,severalpoints

(B)havebeenselectedbetweenthelineofpiles(x¼d)andthe

pointA(x

A

¼dþL

hog

)spaced0.5mfromeachotheralongthe

hpairofpointsðA;BÞ,thedeflection

encyversusnormalizedspacingatdifferentvaluesof

pilelength(shadedareasareenvelopesofηforV

0

intherangefrom

0.5%to2.5%)

JOURNALOFGEOTECHNICALANDGEOENVIRONMENTALENGINEERING©ASCE/MARCH2011/259

J. Geotech. Geoenviron. Eng. 2011.137:254-262.

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encyoftheaveragehorizontaldeformationonthe

spacingbetweenpiles(L

hog

¼10m),experimentalandnumerical

results

nceofthepilespacingonthereductionofdamage

category(L

hog

¼10m)

ratioΔ=Lwascalculatedalongthechordofthegreenfieldsettle-

mentprofilejoiningthesettlementS

A

withS

B

,asshowninEq.(2)

ðΔ=LÞ

AB

¼ð1=L

AB

Þ½jS

B

jÀjx

Δ

Àx

B

jjS

B

ÀS

A

j=L

AB

ÀjSðx

Δ

Þj

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