RESEARCHPAPERFinite-element modeling of a complex deep
excavation in ShanghaiY.M.Hou J.H.Wang L.L.ZhangReceived:25June2007
/ Accepted:14February2008 /
Publishedonline:15August2008Springer-Verlag2008Abstract The
excavation of the north square under-ground shopping center of
Shanghai South
RailwayStationisacomplexdeepexcavationusingthetop-downconstructionmethod.
The excavation has a
considerablesizeandisclosetotheoperatingMetroLines.Inordertopredict
the performance of the excavation more accu-rately, 3D nite-element
analyses are conducted
tosimulatetheconstructionofthiscomplexexcavation. Theeffects of the
anisotropic soil stiffness, the adjacentexcavation,
andzoneexcavationonthewall deformationareinvestigated.
Itisshownthatthenumericalsimulationwith anisotropic soil stiffness
yields a more reasonablepredictionof the wall deectionthanthe case
withiso-tropic soil stiffness. The deformation of the
shareddiaphragmwallbetweentwoexcavationsisinuencedbythe
construction sequence of the two excavations.
Thezonedexcavationcangreatlyreducethediaphragmwalldeformation.
However, onlythezonedexcavationat therst
excavationstageaffectsthedeformationofthewallssignicantly.
Whenthedepthoftheexcavationincreases,thezonedexcavationhasminoreffectonthedeformationof
diaphragmwalls.Keywords Anisotropicstiffness Deepexcavation
3Dnite-elementmethod Zonedexcavation1
IntroductionWiththerapidincreaseof
constructioninurbanareasofShanghai, more and more excavations are
constructedadjacent tothe existing MetroLines or sensitive
super-structures. Theimpact of
theexcavationsonsurroundingstructuresisa
majorconcern.Theexcavationforthenorthsquare underground shopping
center of Shanghai SouthRailway Station was a large size, complex
deep excavation.Thedepthoftheexcavationwas14.7mandthetotalareaof
theexcavationwas40,000m2. It wasonlyabout
3mawayfromtheoperatingShanghaiMetroLinesNo.1andNo. 3. In addition,
the excavation of the interchange stationofMetroLinesNo. 1andNo.
3waslocatedbesidesthisexcavationinthenortheastandwascarriedoutduringtheconstruction
of this excavation. A reliable prediction of theperformance of this
excavation is therefore essential indesignstage.After its rst
application to the analysis of excavation
byCloughetal.[2],thenite-element(FE)methodhasbeenusedtopredict soil
deformations andwall deections inmany research studies [35, 8, 9,
11, 13]. FE analysis couldestimate the wall deections of
complexexcavations bysimulating various construction sequences. The
accuracy ofthenumerical analysisismainlyaffectedbytheconstitu-tive
models of the soil. Ng et al. [10] illustrated thesignicance of
inherent stiffness anisotropy on
grounddeformationarounddeepexcavations. Generally, thesoilsin
Shanghai are sedimentary soils, which are depositedthrough
sedimentation followed by consolidation underaccumulative
overburden. Zhao et al. [16] performed aY. M.Hou(&) J.H. Wang
L. L.
ZhangCivilEngineeringDepartment,ShanghaiJiaotongUniversity,1954HuaShanRoad,
Shanghai, Chinae-mail:[email protected].
H.Wange-mail:[email protected]. L.
Zhange-mail:[email protected]
3ActaGeotechnica(2009)4:716DOI10.1007/s11440-008-0062-3series of
oedometer tests to investigate the
inherentanisotropyofasiltyclayinShanghai. Soil samplesweresliced at
certain angles, i.e., 0, 15, 30, 45, 60, 75,
and90,totheplaneofdepositionandextractedfromthesoillayer for the
oedometer tests. They found out that
thecoefcientsofcompressibilityofthesiltyclay, arediffer-ent for
soil samples with different sampling angles
(Fig.1).ThecompressibilityofthesiltyclayinShanghaigenerallyincreases
withthe samplingangle. Therefore, it
maybenecessarytoconsidersoilanisotropyinnumericalanalysisof deep
excavation in Shanghai in order to obtain a
realisticpredictionofgroundmovementoftheexcavation.In this paper,
3D nite-element modeling is used to studythe performance of this
large size complex excavation of thenorth square underground
shopping center of ShanghaiSouthRailwayStation.
Thedetailedconstructionprocessincludinginstallationof
foundationpiles
anddiaphragmwalls,zonedexcavationandinstallationofhorizontalsup-portsystemissimulated.
Thecalculatedwalldeectioniscompared with the observed performance.
The effects of theanisotropic soil stiffness, the adjacent
excavation, and zoneexcavationonthewalldeformationareinvestigated.2
GroundconditionsandconstructionsequencesThe excavation site of the
north square undergroundshopping center of Shanghai South Railway
Station islocatedonthesouthofShanghai.
Figure2showsthelay-outoftheexcavation.Theexcavationwasonlyabout3mawayfromtheexistingtunnelsof
Shanghaimetroline No.1andNo. 3, whichwereonthenorthwest
andnortheastside of the excavation, respectively. The newroute
ofShanghaimetrolineNo.1wasintheeastofthesite.The04.0x10-45.0x10-46.0x10-47.0x10-48.0x10-49.0x10-4
() p=0~50 kPa p=50~100 kPa p=100~200 kPa p=200~400 kPaCoefficent of
compressibility: a 15 30 45 60 75 90Surface of thedepositionCut
planeAngle of soil samplingFig.1 The relationship between the
coefcient of compressibility and the angle of soil sampling of a
silty clay in Shanghai (modied from Zhaoetal. [16])Shanghai south
railway staitionNew metro line No. 1 (planned)Metro line
No.1Diaphragm wallI1I2I3I4 I5 I6 I7I11I13I16I19I21I22I23I24 I25
I27I26I18I20I17 I15I14I12 I10I9I8I28I29I30I31I32I33I38I39I40I41I37
I36I35I34Inclinometers in wallMetro line No.3Excavation site of
interchange station of metro line No. 1 and No. 3NScale0 10
20(m)123456Inclinometers in soilIT10IT1IT2IT3IT4 IT5
IT6IT7IT8IT9IT11Fig.2
Thelocationandinstrumentationoftheexcavationsite8
ActaGeotechnica(2009)4:7161
3minimumdistancebetweentheexcavationandthetunnelwas only 2m. In
addition, the excavation of the inter-change station of Metro Lines
No. 1 and No. 3 was locatedbesides this excavationinnortheast
andwas constructedbefore this excavation. The retaining walls of
the twoexcavationsweresharedbybothexcavations.
Tomonitortheperformanceoftheexcavation, asshowninFig. 2,
41inclinometers I1I41 were installed in the diaphragm
wallstomeasuretherotationanddeectionsof thewalls. Theinclinometers
IT1IT11 was installed to monitor
thegroundmovementnearthemetrotunnel.According to the site
investigation report, the site isunderlain by thick, relatively
soft, quaternary alluvial,andmarinedeposits. As showninFig. 3,
thesubsurfaceconsist of a 1.2m thick ll layer, which is
mainlymediumdensesand. Beneaththell layer,
thereisa2mthicksiltyclaylayer. Twolayers of verysoft siltyclaywith
total thickness of 16.8mare underneath the siltyclay layer. The
subsequent soil layers are a silty sandlayer, asiltyclaylayer
andasiltysandlayer. InFig. 3,thevariationof soil properties, i.e.,
thesoil unit weight,the water content, the void ratio of the soils,
the com-pression index of the soils, etc., with the depth
areillustrated. It canbeseenthat thesoilsinthisexcavationsite are
generallysoft soils withlowshear strengthandlowmodulus of
deformation.5040302010016 18 20 20 40 600.5 1.0 1.5 0.5 1.0 0 40 80
0 20 40 0 20 40Silty sandSilty clayVery soft silty clay Soil
layersDepth (m)FillSilty claySilty sand 241 - 1t
(kN/m3)wwlwpw,wl,wp (%) e CcSu (kPa) c (kPa) ()Fig.3
SoilprolesandvariationofsoilpropertieswithdepthFig.4
CrosssectionAAoftheexcavationActaGeotechnica(2009)4:716 91
3Figures4and5present theretainingstructures of
theexcavationincrosssections AAandBB, respectively.The excavation
was 14.7m deep with two basement levelsandwas
supportedby0.8mthickdiaphragmwalls.
Thedepthofthediaphragmwallswasabout24m.Asthetop-downmethodwasadopted,
threelevelsof concreteoorslabs were employedtosupport the
diaphragmwalls atdepths of-3.0, -8.45, and -14.7m. The site of
theinterchange station of Shanghai metro line No. 1 and No. 3was
adjacent to the excavation site. The
12.1mdeepexcavationofthatsitewasconductedusingthebottom-upmethod.
A0.8mthickand27.85mdeepdiaphragmwallwas adoptedas the
earth-retainingstructure of that site.There were three levels of
steel struts to support theexcavation, which were at elevations of
-2.83, -6.43, and-9.83m, respectively.
Thediaphragmwallsbetweenthetwoexcavationsweresharedbybothexcavations.Theconstructionsequencesofthisexcavationtogetherwith
the excavation of the interchange station are asfollows:1.
Stage1:excavateto-3.75m2. Stage2:installdiaphragmwallsandpiles3.
Stage3: excavatetheadjacent
siteoftheinterchangestationtothebottom(-12.1m)andinstallsteelstruts4.
Stage 4:constructtheroofslab(B0F)at -3.00mandthenexcavateto-7.50m5.
Stage5:excavateto-10.00m6. Stage 6: construct the rst oor slab
(B1F) at -8.45mandthenexcavateto-12.00m7.
Stage7:excavatetothebottomoftheexcavationandconstructthesecondoorslab(B2F).Toreducethewall
deectionduringtheconstruction, theexcavation is carried out in
layers and zones and
theconcreteoorslabswerealsocastbyzones.ThesequenceofthezonedexcavationisshowninFig.
2.3 Finite-elementmodelingoftheexcavationA3Dnite-element model
(1,200m9500m980m)wasestablishedusingthegeneral-purposenonlinearnite-elementanalysisprogramsuiteABAQUS.
ThemeshesoftheentiremodelandtheretainingstructuresareshowninFig. 6.
The 3Dsolidelements were used for soils. Thecolumns and girders of
the structure are simulated bybeamelements. The diaphragmwalls and
the concreteoor slabs aremodeledusingshell elements. Theentire3D
model consists of 155,306 elements and 178,053nodes.
Toreducethecomputationload, all
theelementsarelinear-orderelements.Thefoursideboundarysurfacesare
xed along the direction perpendicular to each sur-face.
Thebottomboundaryis constrainedalongall x, y,andzdirections.The
diaphragm walls, the steel columns, the RC piles ofthe foundation,
and the oor slabs are modeled as isotropiclinear-elastic materials.
The Youngs modulus and thePoissons ratio of the concrete are taken
as 30GPa and
0.2,respectively,whilethoseofthesteelaretakenas211GPaand0.3,respectively.Considering
the complexity of the 3Dnite-elementmesh, the difculties of
numerical modeling and thecomputationtime, itisreasonabletomodel
soilaselasticmaterial.
Asthesoilsinthesitearegenerallyquaternaryalluvialandmarinesoils,depositedthroughtheprocessofsedimentation
followed by consolidation in horizontallayers, theanisotropyof soil
propertiesneedstobecon-sideredinthenumericalanalysis. Inthisstudy,
twocaseswith different soil stiffness, i.e., one with the
isotropicsoil properties andthe other withanisotropic soil
prop-erties, are conducted. In the case with anisotropic
soilproperties, the soils are assumedtobe
cross-anisotropicmaterials with inherent anisotropy. The
stress-inducedanisotropyandthechangeofthedegreeofanisotropyduetoexcavation
are ignored. For an idealized cross-aniso-tropic elastic material,
the stress-strain behavior isgovernedbyveindependent
elasticparameters: Eh, Ev,Gvh, mvhand
mhh,whereEhandEvaretheYoungsmoduliinthehorizontal andvertical
directions, respectively;Gvhis the shear modulus in any vertical
plane; mhhis thePoissons ratiofor the effect of horizontal
strainonthecomplementaryhorizontal plane;
andmvhisthePoissonsratiofor theeffect of vertical
strainonhorizontal strain.As the stress path of the soils around an
excavationcorresponds approximately to a triaxial extensionFig.5
CrosssectionBBoftheexcavation10 ActaGeotechnica(2009)4:7161
3condition[12],theextensionmoduliofthesoilsshouldbeused in the
numerical analysis. Becker [1] summarizedthe undrained anisotropic
elastic parameters for variousclays based on experiment results.
The ratio of Eh/Evrangesfrom0.5to2.4,andtheratioof
Gvh/Evvariesfrom0.23to0.44. Lee [7] suggestedthat the ratioof
Gvh/Evshouldbe40-100%of thevalueof G/Eunder isotropiccondition. In
this study, the Youngs modulus in thevertical direction, Ev,
isassumedtobefour timesof themodulus of compressibility Ec, which
was determinedby laboratory oedometer tests. The ratios of
Eh/EvandGvh/Evof the soils are assumed to be 0.6 and 0.26,Fig.6
Meshofthe3Dnite-elementmodelActaGeotechnica(2009)4:716 111
3respectively. Table1presents the list of soil parametersadoptedfor
thecasewithanisotropicsoil properties. Forthe case with isotropic
soil properties, the Youngsmodulus E and the Poissons ratio m are
equal to the valuesof EvandmhhinTable1. The effects of
theanisotropicsoilstiffnesswillbediscussedinthenextsection.Numerical
analysis was performedfollowingthecon-struction sequence of the
excavation. The
detailedconstructionprocesssuchasinstallationofpilesanddia-phragmwalls,
theconstructionof
theinterchangestationexcavationandthezonedandlayeredexcavationarealsosimulated.
The effects of the adjacent excavation andzoned excavation
procedure will be presented and dis-cussedinthenextsection.4
Resultsofnumericalanalysisanddiscussion4.1
EffectsofanisotropicsoilstiffnessFigure7 presents the contours of
the wall deections of
thediaphragmwallsforthecasewithanisotropicsoilproper-ties. The
3Dbehavior [15] of the diaphragmwalls
isillustratedclearlyinthisgraph. Thewall
deectionsnearthecornersaremuchsmallerthanthoseofthewallsnearthecenter.
Thewall deectionis alsoinuencedbytheshape of the wall. For those
panels forming a wall with arcshape,
thelateraldisplacementsofthewallsarerelativelysmall.Figure8showsthecalculatedwall
deectionsandtheeldmeasurementsatinclinometersI6andI29duringthewhole
process of the excavation. The inclinometer
I6isclosetotheplannednewtunnelsofmetrolineNo.
1andtheinclinometerI29isadjacent totheexistingmetrolineNo.1.
Atstage4,the wallwaspropped by theroofslabattheelevationof -3.00m.
Duetotheexcavationof pre-vious stages, the diaphragm wall moved
towards theexcavation. With the subsequent excavation, the
walldeectioncontinuedtoincrease. At thenal stageof theexcavation,
adeep-seateddeectedshapeofthewall wasobserved and the maximum wall
deection occurredaround the bottomof the excavation. The ratios of
themaximummeasuredwalldeectiontothenalexcavationdepth at the
inclinometers I6 and I29 were 0.34 and 0.32%,respectively, whichare
withinthe range of the reportedvaluesin[14].AccordingtoFig. 8,
thecalculatedwall deectionsofthe anisotropic case agree well
withthemeasuredones,whilethecalculatedwall
deectionsoftheisotropiccaseare generally smaller than the eld
measurements. Thecomputed maximumwall deections for the
anisotropiccasewereabout
24.5and37.9%largerthantheisotropiccaseatI6andI29, respectively.
Themaximumdifferencebetween the measured and calculated deection
for theanisotropic case is about 8%. However, the
maximumdifferencebetweenthemeasuredandthecomputedresultsfor the
isotropic case is about 30%. Therefore, the soilmodels with
anisotropic stiffness can signicantly improveFig.7
Thecontoursofthecalculatedwalldeectionsatstage7forthecasewithanisotropicsoilstiffness(unit:mm)Table1
SoilparametersusedinnumericalanalysisSoillayerno. Soiltype
ct(kN/m3) K0Ec(kPa) Eh(MPa) Ev(MPa) Gvh(MPa) mvhmhh Fill 19.1 0.50
5,530 13.27 22.12 6.2 0.33 0.35` Siltyclay 19.5 0.50 3,870 9.28
15.48 4.0 0.29 0.30 Verysoftsiltyclay 17.8 0.55 3,040 7.29 12.16
3.16 0.33 0.35 Verysoftsiltyclay 17.0 0.64 2,090 5 8.36 2.17 0.37
0.422Siltysand 18.5 0.52 13,750 33 55 14.3 0.29 0.304Siltyclay 24.3
0.43 20,250 48.6 81 21.06 0.29 0.301-1Siltysand 19.3 0.43 120 200
520 0.29 0.3012 ActaGeotechnica(2009)4:7161 3the accuracy of the
prediction of the wall deection for
thesitewithhorizontallydepositedsoils.Figure9illustrates thesoil
displacement
inhorizontaldirectionatinclinometerIT10.Themaximumvalueoftheobserved
horizontal soil movement at IT10 was about18mm, whichis muchsmaller
thanthe maximumwalldeection of the inclinometer I29. This shows
that theretainingstructureof
theexcavationreducedthegroundmovementandthedeformationoftheoperatingtunnelsofmetrolineNo.
1iswell controlled. Thecomputedmaxi-mum ground movement of the
anisotropic case is 18.4mm,while the computedmaximumgroundmovement
of theisotropiccaseisonly14.7mm. Obviously, thenumericalanalysis
with anisotropic soil parameters yields
betterestimationofthemaximumlateralgroundmovement.4.2
EffectofadjacentexcavationTheexcavationoftheinterchangestationofMetroLinesNo.
1andNo. 3was locatedbesides this excavationinnortheast side and was
excavated to the bottom level beforetheconstructionof theroof
slabof this excavation. Thediaphragm walls between the two
excavations were shared.Figure10illustrates
the3Ddeformationbehavior of
thediaphragmwallsaroundtheexcavationoftheinterchangestation. It
canbeseenthat thedeections of theshareddiaphragmwalls are smaller
than those of other wall-30-25-20-15-10-500IT10Lateral displacement
(mm)Depth (mm) Measured Anisotropic Isotropic10 20 30Fig.9 Effect
of theanisotropicsoil
stiffnessonthecalculatedsoillateraldisplacementatinclinometerIT10Fig.10
Thecontoursof thecalculatedwall deectionsaroundtheexcavation of the
interchange station at a stage 3 and bstage
7(unit:mm)-30-25-20-15-10-500 10 20 30 40(Measured Anisotropic
Isotropic )Stage 7 Stage 4Lateral displacement (mm)Depth (m)Stage
60 10 20 30 40 0 10 20 30 40I6I6 I6(a)-30-25-20-15-10-500 10 20 30
40Stage 7 Stage 4Lateral displacement (mm)Depth (m)(Measured
Anisotropic Isotropic )Stage 60 10 20 30 40 0 10 20 30 40I29I29
I29(b)Fig.8 Effect oftheanisotropicsoil
stiffnessonthecalculatedwalldeectionsatainclinometerI6andbinclinometerI29ActaGeotechnica(2009)4:716
131 3sections. This is because the deformation of the sharedwalls
is affected by the excavation process on both sides ofthe walls.
After the excavation of the interchange station isnished,
themaximumdisplacement of thesharewall isabout 30mm. Whenthe
excavationof the northsquarestarts, thesharedwall starts
tomovetothesideof thatexcavation,
andhencethedeectionofthesharedwall isreduced.Figure11 shows the
measured and calculated deec-tions of the shared diaphragm wall at
the inclinometers I16and I18. In each diagram the wall deection is
greater thanzero, it means that the wall moves to the side of
theexcavationofthenorthsquare. Ifthelateraldisplacementof thewall
isnegative, it meansthat thediaphragmwallmoves towards the site of
the interchange station. Thecalculatedwalldefectionsarefor
thecasewithanisotropicsoilproperties.Accordingtotheeldmeasurements,
after thesiteoftheinterchangestationwasexcavated, thewall
graduallymovedtowardsthesideofthat excavation. Whenthesiteof the
interchange station was excavated to the bottomlevel,
themaximumwall deectionsat
inclinometersI16andI18were35.5mmand34.7mm, respectively. Afterthe
excavation of the north square started, the
shareddiaphragmwallmovedtowardsthesideofthatexcavationand the wall
deection was reduced. At stage 7, the-35-30-25-20-15-10-5010Stage
4Lateral displacement (mm)Depth (m)(measured calculated
)Interchange station excavation sideStage 3I 16Stage 7 Stage
6(a)-35-30-25-20-15-10-50Stage 4Lateral displacement (mm)Depth
(m)(measured calculated )Interchangestation excavationsideStage 3I
18Stage 7 Stage 6(b)0 -10 -20 -30 -40 10 0 -10 -20 -30 -40 10 0 -10
-20 -30 -40 10 0 -10 -20 -30 -4010 0 -10 -20 -30 -40 10 0 -10 -20
-30 -40 10 0 -10 -20 -30 -40 10 0 -10 -20 -30 -40Fig.11 Comparison
of the observed and calculated wall deection of the shared
diaphragm wall between the excavations at a inclinometer
I16andbinclinometerI1814 ActaGeotechnica(2009)4:7161
3maximumdeection at inclinometer I16 and I18 were16.45mmand12.32mm,
respectively. Thepoint of themaximumwall
deectionmovedupwardsfromaround-14mat stage3to-11mat stage7.
However, as
indi-catedinFig.11,evenaftertheexcavationwascompleted,the shared
wall still deected towards the site of theinterchangestation,
especiallythelowerpartofthewalls,which is below the bottomof the
excavation of theinterchangestation.As showninFig. 11,
thecalculatedresults of the3Dnite-element analysisagreewell
withtheeldmeasure-ments except for the nal two stages. For
inclinometer I18,theshapeof thecalculatedwall
deectionandthemea-suredoneat stage7aredifferent.
Thereasonisprobablythatafterthesiteoftheinterchangestationwasexcavatedtothe
bottomlevel, the steel struts were demolishedinzones and the
concrete slabs were cast subsequently.However, it wouldtakeseveral
daysbeforetheconstruc-tionofallconcrete slabswere
nishedandthewholeoorslab was formed to support the walls.
Therefore, the lateralmovement of the shared diaphragmwalls was
mostlyinuencedbytheexcavationofthenorthsquare.Whileinthe3Dnite-elementanalysis
ofthisstudy,thesteelstrutsin the interchange station site are kept
during the con-struction of the excavation of north square.
Thedemolishment of the steel struts and the construction of
theconcreteslabof theadjacent interchange stationarenotmodeled as
the detailed construction sequence of the site
oftheinterchangestationisnotavailable.4.3 EffectofzonedexcavationIn
order to investigate the effect of zoned excavation on
thewalldeformation,twotypesof3Dnite-elementanalysis,zonedexcavation,andunzonedexcavation,areperformed.Theconstructionsequenceemployedinthestudiesoftheprevioussectionsistermedaszonedexcavation,
inwhichthesoilsareexcavatedbyzonesasshowninFig. 2.Inthecaseof
unzonedexcavation, thesoilsareremovedintheentireexcavationareaat
onceineachstageof theexca-vation.
Inbothcases,thesoilpropertiesareanisotropic.Figure12 presents the
comparison of the calculated walldeectionsat inclinometer I6for
thecasesof zonedandunzoned excavation. As indicated in this gure,
zonedexcavationhassignicanteffectonthewalldeection.Atstage 4, the
shape of the wall deectionof the case ofunzoned excavation is
cantilever-type, which is signi-cantly different fromthe observed
shape of the walldeection. It is because in the case of zoned
excavation,
theroofconcreteslabisconstructedsoonaftertheexcavationineachzoneandthereforetheconcreteslabintheexca-vatedzoneandthesoilsintheunexcavatedzonerestrictthe
deformation of the walls. However, in the case ofunzonedexcavation,
thesoilsabove-7.0mareremovedallatonceatstage4andthewallsdeectwithoutsupportof
theroof concreteslab. After theroof slabis cast, thedisplacement at
the top of the wall remains unchanged
andthedeectionofthelowerpartofthewallisrestrictedbytheoorslabsduringthesubsequent
stageofexcavation.When the excavation is completed, the
maximumwalldeectionatinclinometersI6oftheunzonedexcavationis51.5%larger
thanthat of thezonedcase. Therefore,
thezonedexcavationcangreatlyreducethediaphragmwalldeformation.Ouet
al. [15] studiedthe effect of
zonedexcavationusingnite-elementanalysis.However,
thecomparisonof-30-25-20-15-10-500 20 40 60Stage 7 Stage 4Lateral
displacement (mm)Depth (m)(Measured Zoned Unzoned )Stage 60 20 40
60 0 20 40 60I6 I6 I6Fig.12 The effect of zoned excavation on the
wall deection atinclinometerI6-30-25-20-15-10-50-4Incremental wall
displacement (mm)Depth (m) Zoned Unzoned-2 0 2 4 6Fig.13
Incremental wall deection at inclinometer I6 from stage 6
tostage7ActaGeotechnica(2009)4:716 151 3zoned excavation and
unzoned excavation is performedonlyforthenalstage. Therefore,
thedifferencebetweenzoneandunzonedexcavationsappearstobeinsignicant.Figure13presents
theincremental deectionof
thedia-phragmwallatinclinometerI6fromstage6tostage7. Itcanbe
seenthat at thenal stage, theincremental walldeection is only
slightly affected by the zoned excavation.This observation agrees
with the ndings by Ou et al. [15].AccordingtoFig. 12andFig.
13,zonedexcavationattherst
excavationstagesignicantlyaffectsthedeformationofthewalls.
Whenthedepthoftheexcavationincreases,zonedexcavationhaslesseffect
onthedeectionofdia-phragmwalls.5 ConclusionsThispaper
presentsa3Dniteelement modelingfor
theexcavationofthenorthsquareofShanghaiSouthRailwayStation.Thefollowingconclusionscanbemade:1.
Theassumptionofsoil stiffnesshassignicant effecton the wall
deformation. The numerical simulationwithanisotropicsoil
stiffnessyieldsbetter predictionof the wall deection compared with
the case withisotropicsoilstiffness.2. The deformation of the
shared diaphragm wallbetween twoexcavations is inuencedby
constructionsequenceofbothexcavations.3. For alargeexcavation,
zonedexcavationcangreatlyreduce the diaphragmwall deformation.
However,onlythezonedexcavationattherstexcavationstageaffects the
deformation of the walls signicantly.When the depthof the
excavation increases, the zonedexcavation has minor effect on the
deformation ofdiaphragmwalls.Acknowledgments This studywas
substantiallysupportedbythegrants from the National Natural Science
Foundation of China (GrantNo. 50679041) and the Shanghai Municipal
Sciences and TechnologyCommittee(GrantNo.04DZ12001).References1.
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