CaseStudyandNumericalSimulationofExcavationbeneath ...gauge’s initial frequency; F i is the...

Research ArticleCase Study and Numerical Simulation of Excavation beneathExisting Buildings

Hua-feng Shan 123 Shao-heng He2 Yu-hua Lu3 and Wei-jian Jiang3

1School of Civil Engineering and Architecture Taizhou University Taizhou 318000 China2Research Center of Coastal and Urban Geotechnical Engineering Zhejiang University Hangzhou 310058 China3Fangyuan Construction Group Co Ltd Taizhou 318000 China

Correspondence should be addressed to Hua-feng Shan shanhfzjueducn

Received 9 July 2020 Revised 11 October 2020 Accepted 15 December 2020 Published 30 December 2020

Academic Editor Hui Yao

Copyright copy 2020Hua-feng Shan et alis is an open access article distributed under the Creative CommonsAttribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Excavation beneath existing buildings may cause the superstructure to tilt and crack which seriously affects the normal use of thesuperstructure Due to the new working conditions of excavation beneath existing buildings related case reports are rare andlimited In the case of No 3 section basement construction project of Ganshuixiang we monitored the excavation construction byburying test instruments at the designated location Afterwards Plaxis 3D finite element software was used to establish anunderpinning pile-cap-excavation model which can analyze the influence of different pile cutting sequences on the bearingbehavior of new basement structural pillars By comparing the in situ measurement data with the finite element model it can beconcluded that when the excavation depth rises the axial force of the underpinning pile gradually increases and the pile skinfriction is slowly exerted from top to bottom Different cutting sequences will influence the bearing behavior of the structuralpillar Moreover the pile cutting process also significantly impacts its bearing behavior and the settlement behavior of thesuperstructure Compared with the clockwise pile cutting sequence the symmetrical pile cutting is more advantageous In thewhole process of the storey adding and reconstruction the superstructure settlement is related to the working condition of diggingand adding layers In the stage from soil excavation to the concrete curing period of the structural pillar it increases slowly withtime and tends to be stable in the concrete curing period However in the pile cutting stage the superstructure settlementincreases sharply and after pile cutting it becomes stable

1 Introduction

With the booming economy and urbanization the size of citiescontinues to expand In this process some ldquourban diseasesrdquobegin to emerge such as traffic jams and parking issues edevelopment of cities is limited by land resources but high-risedevelopment will only increase the density of buildings andreduce their ability to resist catastrophes It makes urbandevelopment enter a vicious circle However the rationaldevelopment of underground space finds a solution to theabove problems Under this background underground proj-ects such as underground parking lots and subways are beingdeveloped As these underground projects all require a largeamount of soil excavation they inevitably change the original

stress field there Adverse consequences are caused includingcracking and differential settlement of surrounding buildings

To this end Chinese and foreign researchers haveconducted in-depth research on this issue For exampleSung et al [1] made an analysis of the impact of subwaytunnel excavation on various adjacent foundation buildingsbased on 2D and 3D finite element models Zhang et al [2 3]and Liu et al [4] studied its influence on the pile foundationZheng et al [5] analyzed the influencing factors includingspacing pile foundation stiffness pile top load and pile endconstraint based on the measured data using finite elementsoftware Similarly Wang et al [6] proposed a calculationmethod for additional deformation of adjacent buildingsinduced by the excavation of foundation pits

HindawiAdvances in Civil EngineeringVolume 2020 Article ID 8817339 14 pageshttpsdoiorg10115520208817339

e above researchers have investigated the influence ofsoil excavation on surrounding architectures However inprojects of excavation beneath existing buildings con-structors will excavate the soil layer under the existingbuilding us the excavation and unloading of the soil willdirectly affect the foundation pilersquos bearing propertiesCurrently some Chinese experts have investigated thisproblem Gong et al [7] and Wu et al [8] explored theinfluence of excavation on the skin friction and the endfriction of the existing pile based on the underground garageexpansion project in the Zhejiang Hotel MoreoverWu et al[9] introduced a hyperbolic load transfer model to inves-tigate the excavationrsquos effect on the bearing properties of theexisting single pile with the load transfer method LaterShan et al [10] considered the complex pile-pile and pile-soilinteractions between group foundation piles and used thismethod to study its effect on the pile top settlement per-formance of group foundation piles In those projects basedon soft soil areas in Hangzhou a softening phenomenonmight be triggered by the skin friction of the pile with the riseof excavation depth [11] erefore Shan et al [12] used theload transfer method to analyze the impact of the under-ground garage project in the Zhejiang Hotel on the pile topsettlement behavior of the existing pile ey introduced thesoftening model of skin friction In projects of excavationbeneath existing buildings the soil excavation will increasethe free length of the foundation pile It may cause bucklinginstability there and lead to catastrophic consequences Tothis end Shan et al [13 14] studied the calculation methodand influencing factors of the critical load for the bucklingand stability of foundation piles

In summary researchers have carried out plenty oftheoretical studies on this topic Due to the new workingconditions of excavation beneath existing buildings that isthe narrow construction surface and sufficient specialconstruction machinery the related case reports are rare andlimited [15ndash17] In the case of No 3 section basementconstruction project of Ganshuixiang we monitored theexcavation construction by burying test instruments in situen the influences of soil excavation on the bearing be-havior of the underpinning pile different pile cutting se-quences on the structural pillarrsquos bearing behavior and theexcavation process on the settlement behavior of the su-perstructure were analyzed using the in situ measurementdata As the superstructure of the project has two floors andone floor locally and the surrounding buildings are rela-tively dense this study only considers the influence of deadload such as the dead weight of the superstructure einfluence of wind load and seismic load is not discussed [18]Afterwards a 3D solid model of 7C cap-underpinning pile-excavation was established through Plaxis 3D finite elementsoftware which can simulate the influence of different pilecutting sequences on the structural pillarrsquos bearing prop-erties It provides guidance for related projects

2 Project Overview

No 3 section basement construction project of Ganshuixiang islocated in Ganshuixiang Zhakou Street Shangcheng District

Hangzhou Zhejiang Province It is adjacent to the WhitePagoda Park Scenic Area ere are no high-rise buildingsaround the project e north and south of this project are No2 section and No 5 section of Ganshuixiang respectively eeast is No 4 section under construction and the west is CherryHill e specific layout is shown in Figure 1

No 3 section of Ganshuixiang has a two-storey framestructure (partially one-storey) no basement Its totalbuilding height is 801m As the load of the superstructure issmall an independent foundation under the pillar with aburied depth of 180m is adopted According to the surveyreport [19] No 3 section basement construction project ofGanshuixiang is located in an area typical of soft soil Itsphysical and mechanical properties are tabulated in Table 1where cs is the soil unit weight c is the cohesion φ is theangle of internal friction Es is the compressionmodulus andμ is Poissonrsquos ratio

No 3 section of Ganshuixiang was completed in 2014Soon the owner discovered that the building had a problem ofinsufficient usable area erefore it was decided to excavate abasement beneath the existing building After completionabout 1700m2 of the usable area was added No 3 sectionbasement construction project of Ganshuixiang started inNovember 2014 and the main structure construction of thebasement was completed in August of the following year

3 Profile of Excavation beneathExisting Buildings

At present case reports of similar excavation projects arerare and limited [15ndash17] erefore this section introducesthe construction procedure of the project against thebackground of No 3 section basement construction projectof Ganshuixiang [20]

e construction process of the project is shown inFigure 2

e specific construction technology is as follows(1) As the high pressure jet grouting pile can not only be

used as the waterproof curtain but also can play therole of retaining soil Hence before soil excavationdifferent forms of jet grouting piles should be con-structed around No 3 section as shown in Figure 3At the same time steel pipes with a 48mm diameterand a 3mm wall thickness were arranged in anequilateral triangle in the high pressure jet groutingpile ey can improve their bending strength

(2) Generally speaking in the foundation pit engi-neering the precipitation depth should be greaterthan the excavation depth of soil [21] is projectrequires the precipitation depth to be at least 050mbelow the excavation face erefore 23 wells with a060m diameter and a 70m depth were arrangedinside and around No 3 section for precipitationincluding 9 precipitation wells (D1) inside the pitand 14 precipitation wells outside the pits (D2)

(3) e excavation depth of the first soil layer was180m that is the buried depth of the independent

2 Advances in Civil Engineering

Table 1 Physical and mechanical nature of soils

Layer no Name cs (kNm3) c (kPa) φ (deg) Es (MPa) μ①-0 Miscellaneous fill mdash mdash mdash mdash mdash①-1 Silty clay 187 89 36 35 035② Clay silt 1855 121 274 105 035③ Sludge 1615 85 29 25 035④ Gravelly silty clay 1900 4000 1380 60 035⑩-1 Fully weathered sandstone 1977 15 035⑩-2 Highly weathered sandstone 250 025⑩-3 Moderately weathered sandstone mdash mdash mdash gt50 025

High pressure jet grouting pile

Precipitation

Excavating the first soil layer

Foundation underpinning

Excavating the second soil layer

Excavating the third soil layer

Foundation slab and pillar

Cutting pile

Figure 2 Construction flowchart of No 3 section basement construction project of Ganshuixiang

1

2

3

4

11871206

5

1900

1592

Cher

ry h

ill

N

Figure 1 Overall arrangement of No 3 section basement construction project of Ganshuixiang (unit m) Note 1ndash5 represent Nos 1ndash5sections of Ganshuixiang

Advances in Civil Engineering 3

foundation In soil excavation it is advisable to useblock segmentation excavation e altitude differ-ence of the excavation face should be controlledwithin 150m and the slope should not be greaterthan 1 15 Afterwards the first layer of soil nailingwall was constructed as shown in Figure 4

(4) e superstructure floor height of this project re-stricts the foundation underpinning equipmenterefore the foundation underpinning in this pa-per used a small drill to drill the hole to the desig-nated elevation en the steel pipe pile with a250mm outer diameter and an 8mm wall thicknesswas placed down to the bearing stratum (⑩-2) asshown in Figure 5 In order to improve the com-pressive strength of the steel pipe pile this projectpoured fine aggregate concrete inside the steel pipepile as shown in Figure 6 Finally a floor slab waspoured to form a whole to bear the load of thesuperstructure us the foundation underpinningwas completed as shown in Figure 7

(5) e second layer of soil was excavated at 30m deepWith the soil excavation around the pile the soilconstraint beside the pile gradually decreased Underthe axial load of the pile top the foundation pilemight buckle and lose stability [13 14] ereforewhen the excavation depth reached 30m steelsupports should be welded between the foundationpiles as shown in Figures 8 and 9 to preventbuckling instability of these piles Afterwards thesecond layer of soil nailing wall was constructed

(6) e third layer of soil was excavated at 442m deepand the third layer of soil nailing wall was con-structed Afterwards the basement cushion andfoundation slab were poured en the originalindependent foundation and foundation beam wereremoved e new basement structural pillar waspoured with a section size of 045times 045m2 asshown in Figures 9 and 10

(7) As the structural pillar is the main vertical forcetransfer component if the strength fails to reach thedesign value cutting off the pile rashly will causecatastrophic consequences in the superstructuresuch as tilt cracking and even collapse ereforethis project strictly followed the specification [22] forthe maintenance cycle of concrete components

(8) In order to improve the utilization rate of the newbasement space the underpinning pile should beremoved in this project First the steel supportsbetween the foundation piles should be removeden we cut off parts of the steel pipe pile at the topand under the pile near the new basement founda-tion slab e air pick was used to remove the fineaggregate concrete in the pipe as shown inFigure 11(a) Finally the whole pile cutting processwas completed by pulling down the rope tied in themiddle of the steel pipe pile as displayed inFigure 11(b) Judging from the in situ pile cuttingsituation the fine stone concrete at the pile top waswell condensed while the concrete under the pilewas poorly condensed and was loose as shown in

S21 S23

S20S22

S24 S25

S16S17S18S19

S15S14S13S12

S11 S10 S9 S8

S1

S2S3S4

S5 S6 S7D1

D2

D2

D2

D2

D2 D2D2 D2

7D

7C

13D

High pressurejet grouting

pile

D1 D1

D1 D1 D1

D2 D2 D2

D2

D2

D2

Tractorroad

New structural pillar

Underpinningpile

S22

D1 D1 D1

Figure 3 Plan of piles and monitoring points in No 3 section basement construction project of Ganshuixiang Note (1) In the constructionprocess we monitored the piles and pillars at the caps of 7C 7D and 13D (2) D1 and D2 are the dewatering well points (3) S1ndashS25 are thesubsidence monitoring points


Figure 12 e reason may be related to thegroundwater level

At this point the main structure of No 3 sectionbasement construction project of Ganshuixiang was com-pleted as shown in Figures 13 and 14

4 Construction Monitoring

Due to the rare cases of similar excavation the influences ofsoil excavation on the bearing behaviors of the underpinningpile and superstructure and the influence of the pile cuttingprocess on the bearing capacity of the structural pillar havenot been clarified erefore in No 3 section basement

construction project of Ganshuixiang the vibrating wirerebar strain gauge was welded beside the steel pipe un-derpinning pile at 7C 7D and 13D caps and the middleposition of the new basement structural pillar respectivelyey can monitor the influences of soil excavation on theunderpinning pilersquos bearing properties and underpinningpile cutting on the new structural pillar as shown in Fig-ure 15 Additionally 25 settlement monitoring points(S1simS25) were set at the corresponding positions of the firstfloor slab as shown in Figure 3 ey were used to monitorthe influence of No 3 section basement construction projectof Ganshuixiang on the settlement behavior of the super-structure According to the technical standard for moni-toring of the building excavation engineering during the

(a) (b)

Figure 5 Predrill the steel pipe pile (a) drill (b) place down the pipe

Underpinningpile

Existingfoundation

High pressuregrouting pile

The first row ofsoil nail

Dewatering well

5532

8010

ndash1800ndash1800

Figure 4 Excavation the first soil layer and construction underpinning pile (unit m)


Underpinningpile

ExistingfoundationSteel support

Two rows of soilnails

Spiral injectionpilesDewatering

well

5532

8010

ndash1800ndash1800ndash3000

Figure 8 Excavating the second soil layer

Figure 6 Underpinning pile after grouting

Figure 7 Formwork for the first floor


basement storey adding and reconstruction the frequency ofthe superstructure settlement monitoring was once everytwo days except during the Spring Festival holidaye axialforce of the underpinning pile was twice a day once in themorning and afternoon During the pile cutting period theaxial force of the underpinning pile and structural columnwas continuously monitored

Due to the space limitation the 7C cap is used in thispaper as an instance to investigate the effect of excavation onthe bearing behaviors of the underpinning pile and struc-tural pillars e layout of vibrating wire rebar strain gaugesis shown in Figure 8

By measuring the frequency variation value of the vi-brating wire rebar strain gauge welded on the outside of thesteel pile the pilersquos axial force value at the correspondingdepth can be converted as follows

e axial force on the vibrating wire rebar strain gauge atthe cross section i is Psgi

Psgi K F20 minus F

2i1113872 1113873 (1)

where K is the calibration coefficient of the gauge F0 is thegaugersquos initial frequency Fi is the vibration frequency ofsection i under a certain load

According to the elastic mechanics [23] the gaugersquosstrain at the cross section i is εsgi

εsgi Psgi

EsgAsg1113872 1113873 (2)

where Asg and Esg are the sectional area and elastic modulusof the vibrating wire rebar strain gauge

Steel support

Pillar

Figure 9 e structural pillar of the new basement and the steel support between piles

Underpinningpile

Existingfoundation

Steel support Bottom slab

Three rows ofsoil nails

Spiral injectionpilesDewatering well

ndash4720 ndash4720ndash4720

5532

8010

ndash1800ndash1800

ndash3000

Pillar

Figure 10 Excavating the third soil layer and pouring new structural pillar


In this paper it is assumed that the deformation iscoordinated between the vibrating wire rebar strain gaugeand the steel pipe pile that is

εsgi εi (3)

where εi is the pile strain at the section of the underpinningpile

en the pile axial force at this section is Pi

Pi EpεiAp (4)

where Ep andAp are the elastic modulus and sectional area ofthe pile

5 Numerical Simulation

51 Soil Model e in situ monitoring test of excavationbeneath existing buildings is not repeatable and the nu-merical software such as finite element can well simulate

Remove the fine aggregateconcrete

(a)

Rope

Underpinning pile

(b)

Figure 11 Cutting off the underpinning pile (a) cutting off the pile (b) pulling down the pile

Loose concrete

Figure 12 Loose concrete at the pile lower part

Figure 13 Main structure of the new basement


various working conditions erefore using Plaxis 3Dgeotechnical engineering finite element software this paperestablished a 3D solid model of 7C cap-underpinning pile-excavation It can analyze the influence of different pilecutting sequences on the bearing behavior of new basementstructural pillars in projects of excavation beneath existingbuildings

Soil is neither an elastomer nor an ideal elastoplasticbody but a complex elastoplastic body [24] Burland [25]pointed out that the soil has great stiffness under the con-dition of small strain and with the increase of strain thestiffness presents a nonlinear decrease erefore we use asmall strain hardening model to simulate the soilrsquos stress-strain relationship

52 Model Parameter ere are many parameters in thesmall strain hardening model Zhang et al [26] and Fanget al [27] studied the stress-related stiffness and recom-mended the relative stiffness of silt and clay as 08 and 10respectively

According to the existing literature [28] the dilatancyangle ψ of sand can be obtained by empirical formula (5)and the dilatancy angle ψ of clay is 0

ψ j minus 30 (5)

G0ref and c07 are the reference shear modulus at the small

strain stage and the corresponding shear strain atGs 070G0 respectivelye parameters G0

ref and c07 can beobtained by the following formulae respectively

Clayey silt

Completely weatheredsandstone

Moderately weathered sandstone

ndash660

ndash870

Underpinning pile

10 ndash1

10 ndash3

2

Vibrating wire rebar strain gauge

180

200

200

200

035

ndash180

055

Highly weatheredsandstone

10 ndash2ndash960

(a) (b)

Figure 15 Layouts of vibrating wire rebar strain gauges in underpinning piles and structural pillars at the cap of 7C (a) layout of vibratingwire rebar strain gauge in the pile (b) layout of vibrating wire rebar strain gauges in the pillar

Pillar

Underpinningpile Dewatering well

Buttom slab

Three rows ofsoil nail


8010

5532

ndash4420ndash4420

Figure 14 New basement diagram


c07 1

9G02c(1 + cos(2)) + σ1 1 + K0( 1113857sin(2)1113858 1113859 (6)

G0 Gref0

c cos minus σ1sinc cos + pref sin

1113888 1113889

m

(7)

where G0 is the small strain shear modulus K0 is the staticEarth pressure coefficient K0 1minus sinφ σ1 is the main stress

e strength parameters can be determined by experi-mental tests and the stiffness coefficient Eref

50 can be obtainedby inversion calculation e remaining parameters can beobtained by the stiffness coefficient Eref

50 and similar engi-neering experience [26 27 29 30] as presented in Table 2

Based on the in situ measurement data the load at thetop of the 7C cap is 67259 kN e concrete strength gradeof the original independent foundation of No 3 sectionbasement construction project of Ganshuixiang is C25 econcrete strength grade of the new basement structuralpillar floor slab roof and cap is C35 whose strength co-efficient can be found in the specification [22] e steel pipepilersquos elastic modulus is 206times109 kPa In this numericalsimulation we utilize the elastic model to analyze the stress-strain relationship of the concrete structure [31ndash33] and theunderpinning pile

53 Modeling Process Considering the boundary effect andcalculation time this model selected the cube with thelength width and height of 40m as shown in Figure 16

Combined with the site construction situation the fol-lowing calculation steps are analyzed to simulate the wholeproject

(1) e initial stress field of soil is applied(2) Activate superstructure loads and isolated founda-

tions Combined with the field measured data thesuperstructure load of the 7C bearing platform is67259 kN

(3) Excavate the first layer of soil to 180m below thesurface that is the embedded depth of independentfoundation

(4) Activate the underpinning pile and pile cap to kill theoriginal shallow foundation

(5) Dig under the soil layere excavation is performedfour times with the first three times at an excavationdepth of 060m and the last at an excavation depth of082m After that the new basement floor andstructural column are activated

(6) e underpinning piles are killed and the recon-struction project is completed

is section mainly studies the influence of clockwisepile cutting and buttress cutting pile on the bearing behaviorof new basement structural columns

6 Discussion

is section will discuss the influence of excavation beneathexisting buildings on the bearing behaviors of the

underpinning pile and new basement structural pillars andits influence on the superstructure settlement behaviorSimultaneously the influence of different pile cutting se-quences on the bearing capacity of structural pillars is an-alyzed using the numerical model

61 Bearing Behavior of Underpinning Piles e excavationbeneath existing buildings will break the initial stress balancebetween the pile and soil In this project the influence ofexcavation depth on the pile axial force is monitored bywelding steel stress meters beside the steel pipe pile asshown in Figure 15 It is worth noting that the soil layer180m below the surface has been excavated before theconstruction of this project erefore the pile axial forcewithin this range remains unchanged and the skin friction iszero

Figure 17 shows that the underpinning pilersquos axial forceincreased with the rise of excavation depth When the burieddepth rose the pile skin friction began to take effect and thepile axial force reduced with the increase of buried depthWhen the excavation depth was 250m the pile axial forcesat 7C cap with buried depths of 235m 435m and 635mwere 1619 kN 9386 kN and 2513 kN respectively When itdeveloped into 442m the pile axial forces at different burieddepths were 1619 kN 1619 kN and 1133 kNe resistanceon the pile end was zero in the whole process

e underpinning pilersquos skin friction can be obtained bydifferentiating the distinction of the pile axial force betweentwo sections by the corresponding contact area ereforethe pile skin friction obtained in the excavation process is theaverage value as illustrated in Figure 18 As is evident theskin friction of the pile was gradually exerted from top tobottom Soil excavation is an unloading process whichmakes the vertical effective stress gradually decrease Usingthe βmethod [34] it is suggested that the pile skin friction inthe shallow layer gradually decreases As the superstructureload of this project remains unchanged the pile skin frictionin the deep layer is gradually exerted

62 Influence of Pile Cutting on the Bearing Behavior ofStructural Pillars Structural pillars are an important verticalbearing component In order to improve the utilization rateof the new basement space the underpinning piles inside thenew basement should be cut off In the pile cutting processthe existing load transfer behavior is changed and the loadof the superstructure is changed from underpinning piles tonew structural pillars At present similar basement exca-vation projects are rare and limited and the influence of thepile cutting process on the bearing behave of structuralpillars has not been reported erefore based on No 3section basement construction project of Ganshuixiang wemonitor the impact of the pile cutting process on the bearingcapacity of underpinning piles by welding steel stress meterson the main reinforcement of new basement structuralpillars as presented in Figure 19 As it suggests when thepile cutting number was enlarged the axial force of thestructural pillar increased sharply For example when thefirst underpinning pile was removed the axial force of the


structural pillar increased from 1467 kN to 9015 kN Itshould be noted that when the underpinning pile ③ wasremoved the axial force increment of the structural pillarreached the maximum It may be caused by the sharp de-crease in the stiffness of the underpinning pile system ereason for the above phenomenon should be related to thecompressive stiffness of the system which is composed ofunderpinning piles and new structural columns

Different pile cutting sequences may affect the bearingcapacity of structural pillars In this section Plaxis 3D finiteelement software was used to establish a 3D solid model of7C cap-underpinning pile-excavation so as to analyze theinfluence of different pile cutting sequences on the bearingbehavior of structural pillars as shown in Table 3 In thetable Fc1simFc4 are the axial force ratios of the structural pillarwhen the first to fourth piles are removedey represent the

Table 2 Soil parameters in the numerical analysis

Soil layer Eref50 (kPa) Eref

oed (kPa) Erefur (kPa) G0

ref (kPa) c07

Miscellaneous fill 4200 2800 10500 31500 00002Clay silt 12600 8400 31500 94500 00002Fully weathered sandstone 18000 12000 45000 135000 00002Highly weathered sandstone 30000 20000 75000 225000 00002Moderately weathered sandstone 60000 40000 150000 450000 00002

40 m

40 m

40 m

YZ

X

(a)

Left

boun

dary

Righ

t bou

ndar

y

Front boundary

Rear boundary

Y

X

(b)

Left

boun

dary

Righ

t bou

ndar

y

Base boundary

Z

X

(c)

Figure 16 ree-dimensional model diagram (a) Grid graph (b) plane figure and (c) front view

0 20 40 60 80 100 120 140 160 180Pile axial force (kN)

2

3

4

5

6

7

8

9

Burie

d de

pth

(m)

Final excavation depth

Excavation depth = 400mExcavation depth = 442m

Excavation depth = 250mExcavation depth = 300mExcavation depth = 350m

Figure 17 Relationship between the excavation depth and axial force of the underpinning pile


ratio between the axial force of the structural pillar whendifferent numbers of underpinning piles are removed andthat when the four underpinning piles are removederefore Fc4 1000 As is evident the axial force of thestructural pillar increased sharply with the increase of thepile cutting number and that different pile cutting sequenceswould have some impact on the axial force of the structuralpillar For the clockwise pile cutting the increment peak ofthe structural pillarrsquos axial force was reached when the fourth

underpinning pile was removed For the symmetrical pilecutting after the third pile was removed the increment peakwas reached with a value of 0342 Later when the fourthpile was removed the increment dropped slightly to 0317 Itcan be seen that different cutting pile sequences have acertain influence on the axial force of new basementstructure pillars and the in situ measured value is close tothe result of symmetrical pile cutting sequences e reasonfor the above phenomenon may be related to the symmetryof the remaining stiffness after pile cutting Compared withthe symmetrical pile cutting the clockwise pile cutting ismore likely to cause uneven stiffness at is after pilecutting is completed the system of remaining underpinningpiles and structural columns will be asymmetrical in stiffnesson both sides Compared with the clockwise pile cuttingsequence the symmetrical pile cutting is more beneficial tothe bearing behavior of the new structural column

63 Influence of Excavation on the Settlement Behavior of theSuperstructure Soil excavation will break the existingequilibrium state and result in additional settlement Forprojects of excavation beneath existing buildings when thesettlement amount or differential settlement amount is toolarge it will have a certain impact on the safety of the su-perstructure erefore the settlement or differential set-tlement of the superstructure is an important factor inexcavation projects In this project 25 settlement moni-toring points (S1simS25) were set on the first floor to monitorthe entire construction process as shown in Figure 20 In thefigure E is soil excavation CTstands for pouring and curingthe concrete floor CA stands for chiseling away the existingcap and foundation beam P means pouring concrete forstructural pillars PC represents the concrete curing periodof the structural pillar and CP is the pile cutting process

Generally speaking the settlement monitoring fre-quency of this project was once every 2 days (except for the


2

3

4

5

6

7

8

9

Burie

d de

pth

(m)

0 10 20 30 40 50 60 70 80 100Excavation depth (m)

90



Figure 18 Relationship between the excavation depth and skin friction of the underpinning pile

3 4210Pile cutting number

700

600

500

400

300

200

100

0

Axi

al fo

rce o

f the

stru

ctur

al p

illar

(kN

)

Cap

Pile cutting sequence

Underpinning pile

44346

67259

15493

9015

1467

3

24

1

Figure 19 Influence of the pile cutting process on the structuralpillarrsquos axial force

Table 3 Influence of different pile cutting sequences on thestructural pillarrsquos axial force

Fc1 Fc2 Fc3 Fc4Clockwise pile cutting 0186 0425 0675 1000Symmetrical pile cutting 0186 0341 0683 1000In situ data 0134 0230 0659 1000


Spring Festival holiday) It can be seen from the figure thatthe superstructure of this project had a small settlement andthe maximum settlement was 61mm (S8 monitoring point)is conforms to the allowable value of building deforma-tion required by the specification [34] indicating that thefoundation underpinning structure of this project is rea-sonable and feasible In the phase between excavation (E)and pouring concrete for structural pillars (P) the buildingsettlement amount gradually increased over time e rea-son may be that the excavation and unloading of the soilhave changed the original stress field and the constructionprocedures from pouring and curing the concrete floor (CT)to pouring concrete for structural pillars (P) cause a largedisturbance to the soil us the soil is reshaped and itdevelops secondary consolidation deformation In theconcrete curing period of the structural pillar (PC) thesettlement amount of the building basically remained un-changed In the pile cutting stage (CP) the settlement of themonitoring point increased by 1ndash23mm It is due to thechange in the superstructure load transfer mechanism Afterthe completion of pile cutting the settlement of the mon-itoring point decreased to different degrees which may berelated to the redistribution of the superstructure load

7 Conclusions

Based on No 3 section basement construction project ofGanshuixiang this paper monitored the basement recon-struction process Moreover we used Plaxis 3D finite ele-ment software to explore the influence of different pilecutting sequences on the bearing behavior of structuralpillars Some conclusions can be drawn as follows

(1) In No 3 section basement construction project ofGanshuixiang the axial force of the underpinningpile increased with the rise of excavation depth and

decreased with the expansion of buried depth eskin friction of underpinning piles was graduallyexerted from top to bottom e resistance on thepile end was always zero in the whole reconstructionprocess

(2) e settlement of the superstructure increased overtime However in the pile cutting process the set-tlement of the building increased sharply After thecompletion of pile cutting the settlement graduallyconverged In the storey adding and reconstructionthe superstructure settlement was related to theworking condition of digging and adding layers Inthe stage of E-PC the settlement of the super-structure increased slowly with time and tended to bestable at PC However in the CP stage the super-structure settlement increased sharply After pilecutting it became stable

(3) e structural pillarrsquos axial force increased significantlywith the increasing pile cutting number Especiallywhen the underpinning pile ③ was removed thestructural pillarrsquos axial force increment achieved themaximum value e structural pillarrsquos axial force wasaffected by different pile cutting sequences Comparedwith the clockwise pile cutting sequence the sym-metrical pile cutting was more advantageous

Data Availability

e data used to support the findings of this study areavailable from the corresponding author upon request

Conflicts of Interest

e authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

is study was supported by the Zhejiang Natural ScienceFoundation Exploration Project (grant no LQ20E080010)Postdoctoral Science Foundation of Zhejiang Province(grant no zj20180081) and General Industrial Projects ofTaizhou Science and Technology Bureau (grant no1801gy22)

References

[1] E Sung H M Shahin T Nakai M Hinokio andM Yamamoto ldquoGround behavior due to tunnel excavationwith existing foundationrdquo Soils and Foundations vol 46no 2 pp 189ndash207 2006

[2] R Zhang J Zheng H Pu L Zhang andH-F Pu ldquoAnalysis ofexcavation-induced responses of loaded pile foundationsconsidering unloading effectrdquo Tunnelling and UndergroundSpace Technology vol 26 no 2 pp 320ndash335 2011

[3] R-J Zhang J-J Zheng L-M Zhang and H-F Pu ldquoAnanalysis method for the influence of tunneling on adjacentloaded pile groups with rigid elevated capsrdquo InternationalJournal for Numerical and Analytical Methods in Geo-mechanics vol 35 no 18 pp 1949ndash1971 2011

7

6

5

4

3

2

1

0

Settl

emen

t (m

m)

S13S16S20

S2S4S8S10

Time (d)0 20 40 60 80 100 120 140 160 180 200

Spring Festival holiday

E CT CA PC CPP

Figure 20 Observed profile of in situ settlement


[4] C Liu Z Zhang and R A Regueiro ldquoPile and pile groupresponse to tunnelling using a large diameter slurryshieldmdashcase study in Shanghairdquo Computers and Geotechnicsvol 59 no 59 pp 21ndash43 2014

[5] G Zheng Z-X Yan H-Y Lei et al ldquoField observation andfinite element numerical simulation analysis of effect onadjacent piles due to excavationrdquo Chinese Journal of Geo-technical Engineering vol 29 no 5 pp 638ndash643 2007

[6] W-D Wang and Z-H Xu ldquoSimplified analysis method forevaluating excavation-induced damage of adjacent buildingsrdquoChinese Journal of Geotechnical Engineering vol 32 no 1pp 638ndash643 2010

[7] X-N Gong C-J Wu F Yu et al ldquoShaft resistance loss ofpiles due to excavation beneath existing basementsrdquo ChineseJournal of Geotechnical Engineering vol 35 no 11pp 1957ndash1964 2013

[8] C-J Wu X-N Gong F Yu et al ldquoPile base resistance loss forexcavation beneath existing high-rise buildingrdquo Journal ofZhejiang University (Engineering Science) vol 48 no 4pp 671ndash678 2014

[9] C-J Wu X-N Gong K Fang et al ldquoEffect of excavationbeneath existing buildings on loading stiffness of pilesrdquoChinese Journal of Rock Mechanics and Engineering vol 33no 8 pp 1526ndash1535 2014

[10] H-F Shan T-D Xia F Yu et al ldquoSettlement of pile groupsassociated with excavation beneath existing basementrdquoChinese Journal of Geotechnical Engineering vol 37 no 1pp 46ndash50 2015

[11] Q-Q Zhang Test and eoretical Study on Bearing CapacityBehavior and Settlement of Pile in Soft Soils Zhejiang Uni-versity Hangzhou China 2012

[12] H-F Shan T-D Xia F Yu et al ldquoSettlement analysis ofbuilding piles associated with excavation beneath existingbasement in soft soilrdquo Journal of Central South University(Science and Technology) vol 47 no 6 pp 1995ndash2000 2016

[13] H-F Shan T-D Xia J-H Hu et al ldquoBuckling stabilityanalysis of pile foundation for excavation beneath the base-ment of existing buildingrdquo Rock and Soil Mechanics vol 36no 2 pp 508ndash512 2015

[14] H-F Shan T-D Xia F Yu et al ldquoBuckling stability analysison critical load of underpinning pile for excavation beneathexisting buildingrdquo Journal of Zhejiang University (EngineeringScience) vol 50 no 8 pp 1425ndash1430 2016

[15] C-H Qiu Y-Q Zhan Y-K Qin et al ldquoStructural design forrenovation and extension of Beijing music hallrdquo BuildingScience vol 15 no 6 pp 28ndash32 1999

[16] Y-W Wen S-Y Liu M-L Hu et al ldquoDeformation controltechniques for existing buildings during construction processof basementrdquo Chinese Journal of Geotechnical Engineeringvol 35 no 10 pp 1914ndash1921 2013

[17] B Simpson J Paul and Vardanega ldquoResults of monitoring atthe British library excavationrdquo Geotechnical Engineeringvol 167 no 2 pp 99ndash116 2014

[18] M A Hariri-Ardebili H Rahmani-Samani andMMirtaherildquoSeismic stability assessment of a high-rise concrete towerutilizing endurance time analysisrdquo International Journal ofStructural Stability and Dynamics vol 14 no 6 Article ID1450016 2014

[19] Zhejiang Engineering Geophysical Exploration InstituteGeotechnical Engineering Investigation Report of No 3 SectionBasement Construction Project of Ganshuixiang ZhejiangEngineering Geophysical Exploration Institute HangzhouChina 2014

[20] China Railway Engineering Design Institute Co Ltd Foun-dation Reinforcement and Underground Auxiliary Facilities ofEndangered Houses in Ganshuixiang China Railway Engi-neering Design Institute Co Ltd Beijing China 2014

[21] JGJ 120-2012 Technical Specification for Retaining and Pro-tection of Building Foundation Excavations China Architec-ture and Building Press Beijing China 2012

[22] GB 50010-2010 Code for Design of Concrete Structures ChinaArchitecture and Building Press Beijing China 2010

[23] S P Timoshenko and J N Gutierr Elasticity eory HigherEducation Press Beijing China 2013

[24] Z-H Xu and W-D Wang ldquoSelection of soil constitutivemodels for numerical analysis of deep excavations in closeproximity to sensitive propertiesrdquo Rock and Soil Mechanicsvol 31 no 1 pp 258ndash264 2010

[25] J B Burland ldquoNinth Laurits Bjerrum memorial lectureldquosmall is beautifulrdquomdashthe stiffness of soils at small strainsrdquoCanadian Geotechnical Journal vol 26 no 4 pp 499ndash5161989

[26] Z-M Zhang K Fang X-W Liu et al ldquoSurrounding groundsettlement control of special double-row structure supportedfoundation pitrdquo Journal of Zhejiang University (EngineeringScience) vol 46 no 7 pp 1276ndash1280 2012

[27] K Fang Z Zhang X Liu Q Zhang and C Lin ldquoNumericalanalysis of the behavior of special double-row supportstructurerdquo Journal of Civil Engineering and Managementvol 19 no 2 pp 169ndash176 2013

[28] R B J Brinkgreve E Engin and W M Swolfs ldquoPlaxis 3D2012 tutorial manualrdquo Plaxis BV Delft e Netherlands2012

[29] W-D Wang H-R Wang and Z-H Xu ldquoStudy of param-eters of HS-small model used in numerical analysis of ex-cavations in Shanghai areardquo Rock and Soil Mechanics vol 34no 6 pp 1766ndash1774 2013

[30] Z-M Zhang Pile Foundation Engineering China Architec-ture and Building Press Beijing China 2007

[31] Z-H Deng H-Q Huang B-L Ye et al ldquoMechanical per-formance of RAC under true-triaxial compression after hightemperaturesrdquo Journal of Materials in Civil Engineeringvol 32 no 8 Article ID 04020194 2020

[32] Z-H Deng B Liu B-L Ye et al ldquoMechanical behavior andconstitutive relationship of the three types of recycled coarseaggregate concrete based on standard classificationrdquo Journalof Material Cycles and Waste Management vol 22 pp 30ndash452020

[33] Z H Deng H Q Huang B Ye H Wang and P XiangldquoInvestigation on recycled aggregate concretes exposed tohigh temperature by biaxial compressive testsrdquo Constructionand Building Materials vol 244 Article ID 118048 2020

[34] GB 50007-2011 Code for Design of Building FoundationChina Architecture and Building Press Beijing China 2011


e above researchers have investigated the influence ofsoil excavation on surrounding architectures However inprojects of excavation beneath existing buildings con-structors will excavate the soil layer under the existingbuilding us the excavation and unloading of the soil willdirectly affect the foundation pilersquos bearing propertiesCurrently some Chinese experts have investigated thisproblem Gong et al [7] and Wu et al [8] explored theinfluence of excavation on the skin friction and the endfriction of the existing pile based on the underground garageexpansion project in the Zhejiang Hotel MoreoverWu et al[9] introduced a hyperbolic load transfer model to inves-tigate the excavationrsquos effect on the bearing properties of theexisting single pile with the load transfer method LaterShan et al [10] considered the complex pile-pile and pile-soilinteractions between group foundation piles and used thismethod to study its effect on the pile top settlement per-formance of group foundation piles In those projects basedon soft soil areas in Hangzhou a softening phenomenonmight be triggered by the skin friction of the pile with the riseof excavation depth [11] erefore Shan et al [12] used theload transfer method to analyze the impact of the under-ground garage project in the Zhejiang Hotel on the pile topsettlement behavior of the existing pile ey introduced thesoftening model of skin friction In projects of excavationbeneath existing buildings the soil excavation will increasethe free length of the foundation pile It may cause bucklinginstability there and lead to catastrophic consequences Tothis end Shan et al [13 14] studied the calculation methodand influencing factors of the critical load for the bucklingand stability of foundation piles

In summary researchers have carried out plenty oftheoretical studies on this topic Due to the new workingconditions of excavation beneath existing buildings that isthe narrow construction surface and sufficient specialconstruction machinery the related case reports are rare andlimited [15ndash17] In the case of No 3 section basementconstruction project of Ganshuixiang we monitored theexcavation construction by burying test instruments in situen the influences of soil excavation on the bearing be-havior of the underpinning pile different pile cutting se-quences on the structural pillarrsquos bearing behavior and theexcavation process on the settlement behavior of the su-perstructure were analyzed using the in situ measurementdata As the superstructure of the project has two floors andone floor locally and the surrounding buildings are rela-tively dense this study only considers the influence of deadload such as the dead weight of the superstructure einfluence of wind load and seismic load is not discussed [18]Afterwards a 3D solid model of 7C cap-underpinning pile-excavation was established through Plaxis 3D finite elementsoftware which can simulate the influence of different pilecutting sequences on the structural pillarrsquos bearing prop-erties It provides guidance for related projects

2 Project Overview

No 3 section basement construction project of Ganshuixiang islocated in Ganshuixiang Zhakou Street Shangcheng District

Hangzhou Zhejiang Province It is adjacent to the WhitePagoda Park Scenic Area ere are no high-rise buildingsaround the project e north and south of this project are No2 section and No 5 section of Ganshuixiang respectively eeast is No 4 section under construction and the west is CherryHill e specific layout is shown in Figure 1

No 3 section of Ganshuixiang has a two-storey framestructure (partially one-storey) no basement Its totalbuilding height is 801m As the load of the superstructure issmall an independent foundation under the pillar with aburied depth of 180m is adopted According to the surveyreport [19] No 3 section basement construction project ofGanshuixiang is located in an area typical of soft soil Itsphysical and mechanical properties are tabulated in Table 1where cs is the soil unit weight c is the cohesion φ is theangle of internal friction Es is the compressionmodulus andμ is Poissonrsquos ratio

No 3 section of Ganshuixiang was completed in 2014Soon the owner discovered that the building had a problem ofinsufficient usable area erefore it was decided to excavate abasement beneath the existing building After completionabout 1700m2 of the usable area was added No 3 sectionbasement construction project of Ganshuixiang started inNovember 2014 and the main structure construction of thebasement was completed in August of the following year

3 Profile of Excavation beneathExisting Buildings

At present case reports of similar excavation projects arerare and limited [15ndash17] erefore this section introducesthe construction procedure of the project against thebackground of No 3 section basement construction projectof Ganshuixiang [20]

e construction process of the project is shown inFigure 2

e specific construction technology is as follows(1) As the high pressure jet grouting pile can not only be

used as the waterproof curtain but also can play therole of retaining soil Hence before soil excavationdifferent forms of jet grouting piles should be con-structed around No 3 section as shown in Figure 3At the same time steel pipes with a 48mm diameterand a 3mm wall thickness were arranged in anequilateral triangle in the high pressure jet groutingpile ey can improve their bending strength

(2) Generally speaking in the foundation pit engi-neering the precipitation depth should be greaterthan the excavation depth of soil [21] is projectrequires the precipitation depth to be at least 050mbelow the excavation face erefore 23 wells with a060m diameter and a 70m depth were arrangedinside and around No 3 section for precipitationincluding 9 precipitation wells (D1) inside the pitand 14 precipitation wells outside the pits (D2)

(3) e excavation depth of the first soil layer was180m that is the buried depth of the independent





Precipitation






Cutting pile


1

2

3

4

11871206

5

1900

1592

Cher

ry h

ill

N









S21 S23

S20S22

S24 S25

S16S17S18S19

S15S14S13S12

S11 S10 S9 S8

S1

S2S3S4

S5 S6 S7D1

D2

D2

D2

D2

D2 D2D2 D2

7D

7C

13D


pile

D1 D1

D1 D1 D1

D2 D2 D2

D2

D2

D2

Tractorroad


Underpinningpile

S22

D1 D1 D1








(a) (b)


Underpinningpile

Existingfoundation



Dewatering well

5532

8010

ndash1800ndash1800



Underpinningpile




well

5532

8010










Psgi K F20 minus F

2i1113872 1113873 (1)



εsgi Psgi

EsgAsg1113872 1113873 (2)


Steel support

Pillar


Underpinningpile

Existingfoundation





5532

8010

ndash1800ndash1800

ndash3000

Pillar




εsgi εi (3)



Pi EpεiAp (4)





(a)

Rope

Underpinning pile

(b)


Loose concrete








ψ j minus 30 (5)




Clayey silt



ndash660

ndash870

Underpinning pile

10 ndash1

10 ndash3

2


180

200

200

200

035

ndash180

055


10 ndash2ndash960

(a) (b)


Pillar


Buttom slab



8010

5532

ndash4420ndash4420



c07 1

9G02c(1 + cos(2)) + σ1 1 + K0( 1113857sin(2)1113858 1113859 (6)

G0 Gref0


1113888 1113889

m

(7)















6 Discussion













ref (kPa) c07


40 m

40 m

40 m

YZ

X

(a)

Left

boun

dary

Righ

t bou

ndar

y

Front boundary

Rear boundary

Y

X

(b)

Left

boun

dary

Righ

t bou

ndar

y

Base boundary

Z

X

(c)



2

3

4

5

6

7

8

9

Burie

d de

pth

(m)











2

3

4

5

6

7

8

9

Burie

d de

pth

(m)


90





700

600

500

400

300

200

100

0

Axi

al fo

rce o

f the

stru

ctur

al p

illar

(kN

)

Cap


Underpinning pile

44346

67259

15493

9015

1467

3

24

1






7 Conclusions






Data Availability




Acknowledgments


References




7

6

5

4

3

2

1

0

Settl

emen

t (m

m)

S13S16S20

S2S4S8S10

Time (d)0 20 40 60 80 100 120 140 160 180 200


E CT CA PC CPP






































Precipitation






Cutting pile


1

2

3

4

11871206

5

1900

1592

Cher

ry h

ill

N









S21 S23

S20S22

S24 S25

S16S17S18S19

S15S14S13S12

S11 S10 S9 S8

S1

S2S3S4

S5 S6 S7D1

D2

D2

D2

D2

D2 D2D2 D2

7D

7C

13D


pile

D1 D1

D1 D1 D1

D2 D2 D2

D2

D2

D2

Tractorroad


Underpinningpile

S22

D1 D1 D1








(a) (b)


Underpinningpile

Existingfoundation



Dewatering well

5532

8010

ndash1800ndash1800



Underpinningpile




well

5532

8010










Psgi K F20 minus F

2i1113872 1113873 (1)



εsgi Psgi

EsgAsg1113872 1113873 (2)


Steel support

Pillar


Underpinningpile

Existingfoundation





5532

8010

ndash1800ndash1800

ndash3000

Pillar




εsgi εi (3)



Pi EpεiAp (4)





(a)

Rope

Underpinning pile

(b)


Loose concrete








ψ j minus 30 (5)




Clayey silt



ndash660

ndash870

Underpinning pile

10 ndash1

10 ndash3

2


180

200

200

200

035

ndash180

055


10 ndash2ndash960

(a) (b)


Pillar


Buttom slab



8010

5532

ndash4420ndash4420



c07 1

9G02c(1 + cos(2)) + σ1 1 + K0( 1113857sin(2)1113858 1113859 (6)

G0 Gref0


1113888 1113889

m

(7)















6 Discussion













ref (kPa) c07


40 m

40 m

40 m

YZ

X

(a)

Left

boun

dary

Righ

t bou

ndar

y

Front boundary

Rear boundary

Y

X

(b)

Left

boun

dary

Righ

t bou

ndar

y

Base boundary

Z

X

(c)



2

3

4

5

6

7

8

9

Burie

d de

pth

(m)











2

3

4

5

6

7

8

9

Burie

d de

pth

(m)


90





700

600

500

400

300

200

100

0

Axi

al fo

rce o

f the

stru

ctur

al p

illar

(kN

)

Cap


Underpinning pile

44346

67259

15493

9015

1467

3

24

1






7 Conclusions






Data Availability




Acknowledgments


References




7

6

5

4

3

2

1

0

Settl

emen

t (m

m)

S13S16S20

S2S4S8S10

Time (d)0 20 40 60 80 100 120 140 160 180 200


E CT CA PC CPP









































S21 S23

S20S22

S24 S25

S16S17S18S19

S15S14S13S12

S11 S10 S9 S8

S1

S2S3S4

S5 S6 S7D1

D2

D2

D2

D2

D2 D2D2 D2

7D

7C

13D


pile

D1 D1

D1 D1 D1

D2 D2 D2

D2

D2

D2

Tractorroad


Underpinningpile

S22

D1 D1 D1








(a) (b)


Underpinningpile

Existingfoundation



Dewatering well

5532

8010

ndash1800ndash1800



Underpinningpile




well

5532

8010










Psgi K F20 minus F

2i1113872 1113873 (1)



εsgi Psgi

EsgAsg1113872 1113873 (2)


Steel support

Pillar


Underpinningpile

Existingfoundation





5532

8010

ndash1800ndash1800

ndash3000

Pillar




εsgi εi (3)



Pi EpεiAp (4)





(a)

Rope

Underpinning pile

(b)


Loose concrete








ψ j minus 30 (5)




Clayey silt



ndash660

ndash870

Underpinning pile

10 ndash1

10 ndash3

2


180

200

200

200

035

ndash180

055


10 ndash2ndash960

(a) (b)


Pillar


Buttom slab



8010

5532

ndash4420ndash4420



c07 1

9G02c(1 + cos(2)) + σ1 1 + K0( 1113857sin(2)1113858 1113859 (6)

G0 Gref0


1113888 1113889

m

(7)















6 Discussion













ref (kPa) c07


40 m

40 m

40 m

YZ

X

(a)

Left

boun

dary

Righ

t bou

ndar

y

Front boundary

Rear boundary

Y

X

(b)

Left

boun

dary

Righ

t bou

ndar

y

Base boundary

Z

X

(c)



2

3

4

5

6

7

8

9

Burie

d de

pth

(m)











2

3

4

5

6

7

8

9

Burie

d de

pth

(m)


90





700

600

500

400

300

200

100

0

Axi

al fo

rce o

f the

stru

ctur

al p

illar

(kN

)

Cap


Underpinning pile

44346

67259

15493

9015

1467

3

24

1






7 Conclusions






Data Availability




Acknowledgments


References




7

6

5

4

3

2

1

0

Settl

emen

t (m

m)

S13S16S20

S2S4S8S10

Time (d)0 20 40 60 80 100 120 140 160 180 200


E CT CA PC CPP








































(a) (b)


Underpinningpile

Existingfoundation



Dewatering well

5532

8010

ndash1800ndash1800



Underpinningpile




well

5532

8010










Psgi K F20 minus F

2i1113872 1113873 (1)



εsgi Psgi

EsgAsg1113872 1113873 (2)


Steel support

Pillar


Underpinningpile

Existingfoundation





5532

8010

ndash1800ndash1800

ndash3000

Pillar




εsgi εi (3)



Pi EpεiAp (4)





(a)

Rope

Underpinning pile

(b)


Loose concrete








ψ j minus 30 (5)




Clayey silt



ndash660

ndash870

Underpinning pile

10 ndash1

10 ndash3

2


180

200

200

200

035

ndash180

055


10 ndash2ndash960

(a) (b)


Pillar


Buttom slab



8010

5532

ndash4420ndash4420



c07 1

9G02c(1 + cos(2)) + σ1 1 + K0( 1113857sin(2)1113858 1113859 (6)

G0 Gref0


1113888 1113889

m

(7)















6 Discussion













ref (kPa) c07


40 m

40 m

40 m

YZ

X

(a)

Left

boun

dary

Righ

t bou

ndar

y

Front boundary

Rear boundary

Y

X

(b)

Left

boun

dary

Righ

t bou

ndar

y

Base boundary

Z

X

(c)



2

3

4

5

6

7

8

9

Burie

d de

pth

(m)











2

3

4

5

6

7

8

9

Burie

d de

pth

(m)


90





700

600

500

400

300

200

100

0

Axi

al fo

rce o

f the

stru

ctur

al p

illar

(kN

)

Cap


Underpinning pile

44346

67259

15493

9015

1467

3

24

1






7 Conclusions






Data Availability




Acknowledgments


References




7

6

5

4

3

2

1

0

Settl

emen

t (m

m)

S13S16S20

S2S4S8S10

Time (d)0 20 40 60 80 100 120 140 160 180 200


E CT CA PC CPP



































Underpinningpile




well

5532

8010










Psgi K F20 minus F

2i1113872 1113873 (1)



εsgi Psgi

EsgAsg1113872 1113873 (2)


Steel support

Pillar


Underpinningpile

Existingfoundation





5532

8010

ndash1800ndash1800

ndash3000

Pillar




εsgi εi (3)



Pi EpεiAp (4)





(a)

Rope

Underpinning pile

(b)


Loose concrete








ψ j minus 30 (5)




Clayey silt



ndash660

ndash870

Underpinning pile

10 ndash1

10 ndash3

2


180

200

200

200

035

ndash180

055


10 ndash2ndash960

(a) (b)


Pillar


Buttom slab



8010

5532

ndash4420ndash4420



c07 1

9G02c(1 + cos(2)) + σ1 1 + K0( 1113857sin(2)1113858 1113859 (6)

G0 Gref0


1113888 1113889

m

(7)















6 Discussion













ref (kPa) c07


40 m

40 m

40 m

YZ

X

(a)

Left

boun

dary

Righ

t bou

ndar

y

Front boundary

Rear boundary

Y

X

(b)

Left

boun

dary

Righ

t bou

ndar

y

Base boundary

Z

X

(c)



2

3

4

5

6

7

8

9

Burie

d de

pth

(m)











2

3

4

5

6

7

8

9

Burie

d de

pth

(m)


90





700

600

500

400

300

200

100

0

Axi

al fo

rce o

f the

stru

ctur

al p

illar

(kN

)

Cap


Underpinning pile

44346

67259

15493

9015

1467

3

24

1






7 Conclusions






Data Availability




Acknowledgments


References




7

6

5

4

3

2

1

0

Settl

emen

t (m

m)

S13S16S20

S2S4S8S10

Time (d)0 20 40 60 80 100 120 140 160 180 200


E CT CA PC CPP







































Psgi K F20 minus F

2i1113872 1113873 (1)



εsgi Psgi

EsgAsg1113872 1113873 (2)


Steel support

Pillar


Underpinningpile

Existingfoundation





5532

8010

ndash1800ndash1800

ndash3000

Pillar




εsgi εi (3)



Pi EpεiAp (4)





(a)

Rope

Underpinning pile

(b)


Loose concrete








ψ j minus 30 (5)




Clayey silt



ndash660

ndash870

Underpinning pile

10 ndash1

10 ndash3

2


180

200

200

200

035

ndash180

055


10 ndash2ndash960

(a) (b)


Pillar


Buttom slab



8010

5532

ndash4420ndash4420



c07 1

9G02c(1 + cos(2)) + σ1 1 + K0( 1113857sin(2)1113858 1113859 (6)

G0 Gref0


1113888 1113889

m

(7)















6 Discussion













ref (kPa) c07


40 m

40 m

40 m

YZ

X

(a)

Left

boun

dary

Righ

t bou

ndar

y

Front boundary

Rear boundary

Y

X

(b)

Left

boun

dary

Righ

t bou

ndar

y

Base boundary

Z

X

(c)



2

3

4

5

6

7

8

9

Burie

d de

pth

(m)











2

3

4

5

6

7

8

9

Burie

d de

pth

(m)


90





700

600

500

400

300

200

100

0

Axi

al fo

rce o

f the

stru

ctur

al p

illar

(kN

)

Cap


Underpinning pile

44346

67259

15493

9015

1467

3

24

1






7 Conclusions






Data Availability




Acknowledgments


References




7

6

5

4

3

2

1

0

Settl

emen

t (m

m)

S13S16S20

S2S4S8S10

Time (d)0 20 40 60 80 100 120 140 160 180 200


E CT CA PC CPP




































εsgi εi (3)



Pi EpεiAp (4)





(a)

Rope

Underpinning pile

(b)


Loose concrete








ψ j minus 30 (5)




Clayey silt



ndash660

ndash870

Underpinning pile

10 ndash1

10 ndash3

2


180

200

200

200

035

ndash180

055


10 ndash2ndash960

(a) (b)


Pillar


Buttom slab



8010

5532

ndash4420ndash4420



c07 1

9G02c(1 + cos(2)) + σ1 1 + K0( 1113857sin(2)1113858 1113859 (6)

G0 Gref0


1113888 1113889

m

(7)















6 Discussion













ref (kPa) c07


40 m

40 m

40 m

YZ

X

(a)

Left

boun

dary

Righ

t bou

ndar

y

Front boundary

Rear boundary

Y

X

(b)

Left

boun

dary

Righ

t bou

ndar

y

Base boundary

Z

X

(c)



2

3

4

5

6

7

8

9

Burie

d de

pth

(m)











2

3

4

5

6

7

8

9

Burie

d de

pth

(m)


90





700

600

500

400

300

200

100

0

Axi

al fo

rce o

f the

stru

ctur

al p

illar

(kN

)

Cap


Underpinning pile

44346

67259

15493

9015

1467

3

24

1






7 Conclusions






Data Availability




Acknowledgments


References




7

6

5

4

3

2

1

0

Settl

emen

t (m

m)

S13S16S20

S2S4S8S10

Time (d)0 20 40 60 80 100 120 140 160 180 200


E CT CA PC CPP







































ψ j minus 30 (5)




Clayey silt



ndash660

ndash870

Underpinning pile

10 ndash1

10 ndash3

2


180

200

200

200

035

ndash180

055


10 ndash2ndash960

(a) (b)


Pillar


Buttom slab



8010

5532

ndash4420ndash4420



c07 1

9G02c(1 + cos(2)) + σ1 1 + K0( 1113857sin(2)1113858 1113859 (6)

G0 Gref0


1113888 1113889

m

(7)















6 Discussion













ref (kPa) c07


40 m

40 m

40 m

YZ

X

(a)

Left

boun

dary

Righ

t bou

ndar

y

Front boundary

Rear boundary

Y

X

(b)

Left

boun

dary

Righ

t bou

ndar

y

Base boundary

Z

X

(c)



2

3

4

5

6

7

8

9

Burie

d de

pth

(m)











2

3

4

5

6

7

8

9

Burie

d de

pth

(m)


90





700

600

500

400

300

200

100

0

Axi

al fo

rce o

f the

stru

ctur

al p

illar

(kN

)

Cap


Underpinning pile

44346

67259

15493

9015

1467

3

24

1






7 Conclusions






Data Availability




Acknowledgments


References




7

6

5

4

3

2

1

0

Settl

emen

t (m

m)

S13S16S20

S2S4S8S10

Time (d)0 20 40 60 80 100 120 140 160 180 200


E CT CA PC CPP



































c07 1

9G02c(1 + cos(2)) + σ1 1 + K0( 1113857sin(2)1113858 1113859 (6)

G0 Gref0


1113888 1113889

m

(7)















6 Discussion













ref (kPa) c07


40 m

40 m

40 m

YZ

X

(a)

Left

boun

dary

Righ

t bou

ndar

y

Front boundary

Rear boundary

Y

X

(b)

Left

boun

dary

Righ

t bou

ndar

y

Base boundary

Z

X

(c)



2

3

4

5

6

7

8

9

Burie

d de

pth

(m)











2

3

4

5

6

7

8

9

Burie

d de

pth

(m)


90





700

600

500

400

300

200

100

0

Axi

al fo

rce o

f the

stru

ctur

al p

illar

(kN

)

Cap


Underpinning pile

44346

67259

15493

9015

1467

3

24

1






7 Conclusions






Data Availability




Acknowledgments


References




7

6

5

4

3

2

1

0

Settl

emen

t (m

m)

S13S16S20

S2S4S8S10

Time (d)0 20 40 60 80 100 120 140 160 180 200


E CT CA PC CPP








































ref (kPa) c07


40 m

40 m

40 m

YZ

X

(a)

Left

boun

dary

Righ

t bou

ndar

y

Front boundary

Rear boundary

Y

X

(b)

Left

boun

dary

Righ

t bou

ndar

y

Base boundary

Z

X

(c)



2

3

4

5

6

7

8

9

Burie

d de

pth

(m)











2

3

4

5

6

7

8

9

Burie

d de

pth

(m)


90





700

600

500

400

300

200

100

0

Axi

al fo

rce o

f the

stru

ctur

al p

illar

(kN

)

Cap


Underpinning pile

44346

67259

15493

9015

1467

3

24

1






7 Conclusions






Data Availability




Acknowledgments


References




7

6

5

4

3

2

1

0

Settl

emen

t (m

m)

S13S16S20

S2S4S8S10

Time (d)0 20 40 60 80 100 120 140 160 180 200


E CT CA PC CPP








































2

3

4

5

6

7

8

9

Burie

d de

pth

(m)


90





700

600

500

400

300

200

100

0

Axi

al fo

rce o

f the

stru

ctur

al p

illar

(kN

)

Cap


Underpinning pile

44346

67259

15493

9015

1467

3

24

1






7 Conclusions






Data Availability




Acknowledgments


References




7

6

5

4

3

2

1

0

Settl

emen

t (m

m)

S13S16S20

S2S4S8S10

Time (d)0 20 40 60 80 100 120 140 160 180 200


E CT CA PC CPP




































7 Conclusions






Data Availability




Acknowledgments


References




7

6

5

4

3

2

1

0

Settl

emen

t (m

m)

S13S16S20

S2S4S8S10

Time (d)0 20 40 60 80 100 120 140 160 180 200


E CT CA PC CPP



































CaseStudyandNumericalSimulationofExcavationbeneath ...gauge’s initial frequency; F i is the...

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Transcript of CaseStudyandNumericalSimulationofExcavationbeneath ...gauge’s initial frequency; F i is the...