Phenomenon and Critical Conditions of Chamber Soil Sliming … · 2020. 7. 14. · Sliming during EPB Shield Tunneling in Water-Rich Weathered Diorite: Case Study of Jinan Metro,

Research ArticlePhenomenon and Critical Conditions of Chamber SoilSliming during EPB Shield Tunneling in Water-Rich WeatheredDiorite Case Study of Jinan Metro China

Lu Wang12 Wei Zhu 3 Yongjin Qian12 Chao Xu12 Jiannan Hu12 and Huitang Xing4

1Key Laboratory of Geomechanics and Embankment Engineering of Ministry of Education Hohai University Nanjing 210098China2School of Civil and Transportation Engineering Hohai University Nanjing 210098 China3School of Environment Hohai University Nanjing 210098 China4Jinan Rail Transit Group Co Ltd Jinan 250000 China

Correspondence should be addressed to Wei Zhu zhuweiteamhhugmailcom

Received 3 January 2020 Revised 26 May 2020 Accepted 24 June 2020 Published 14 July 2020

Academic Editor Chunshun Zhang

Copyright copy 2020 Lu Wang et al )is is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

)e sliming problem of chamber soil is caused by excessive groundwater seeping into the pressure chamber when an Earthpressure balance shield tunnels through a water-rich weathered rock stratum under semiopen under-pressure mode As a solutionto this problem a calculation model was established based on field measurements of the discharged soil properties the seepagewater volume and the seepage path in Jinan Metro China Chamber soil sliming is a phenomenon in which chamber soil is in athin mud state with no pressure balance in the pressure chamber of the EPB shield and an excessive water content of the chambersoil owing to the continuous seepage of groundwater into the chamber )e chamber pressure is relatively low which is differentfrom the phenomenon of spewing when the chamber pressure is relatively high A large amount of water seepage from the stratumaround the tunnel excavation surface and shield to the chamber is a significant factor leading to chamber soil sliming during theconstruction process It was considered that when the moisture content of the chamber soil w is 2wL lewle 3wL slight chambersoil sliming may occur whereas when wge 3wL serious chamber soil sliming may occur Moreover some measures to prevent andcontrol the occurrence of chamber soil sliming were discussed Controlling the advancing time and the permeability coefficient ofchamber soil during construction is the most effective measure to avoid the phenomenon of soil sliming

1 Introduction

In recent years an increasing number of tunnels passingthrough water-rich rock zones have become necessary)ereare abundant case studies and summaries on mountaintunnels based on experience Most mountain tunnels haveadopted a mining method and during the process ofconstruction water inrush and mud outburst accidentseasily occur [1ndash3] However owing to a limitation of anurban environment metro tunnels are usually constructedthrough a shield method which achieves a high level ofsafety However when the geological conditions in front ofthe excavation face are unclear it will lead to an instabilityand water gushing of the excavation face [4 5] At present

there is a lack of case studies and engineering experience onsubway tunnels passing through the rock strata in a city

During construction an Earth pressure balance (EPB)shield is often used under a semiopen under-pressure mode[6ndash8] that is the pressure chamber is not filled with ex-cavated soil and the pressure of the chamber is not applied tobalance the Earth pressure and water pressure at the ex-cavation surface )e principle of EPB shield to maintain thestability of excavation surface is to use the pressure ofchamber soil to balance the Earth pressure and waterpressure on the excavation surface At this time the pressurechamber is full of excavated soil In areas where the stratumcan stand alone steadily and the surface settlement is notvery sensitive in order to pursue a faster construction speed

HindawiAdvances in Civil EngineeringVolume 2020 Article ID 6530832 15 pageshttpsdoiorg10115520206530832

the construction with a nonfull chamber is generallyadopted which will not affect the stability of the excavationsurface at the same time a faster construction speed can beobtained under a smaller thrust and torque and the re-quirements for the chamber soil conditioning are relativelysimple )erefore the construction of semiopen under-pressure mode is common in projects )is type of situationoften occurs in a soft rock stratum which can stand aloneand remain stable as well as in medium-coarse sand and asandy-pebble stratum Under this situation it is difficult toform a plastic flow in the chamber soil )e soil in the plasticflow state is paste-like the permeability coefficient of the soilis less than 10minus 5ms the slump is 150ndash200mm and the highcompressibility usually requires a volume compression rateof at least 2 and low shear strength [9] Owing to thedifficulty in forming a plastic flow of soil in a pressurechamber an EPB shield is prone to spewing [10ndash13]blocking and cake formation [14ndash19] as well as otherphenomena during the construction of such strata )e EPBshield originates from the construction of a soft clay stratumwhich easily forms a plastic flow after being disturbed in thepressure chamber )e soil in the pressure chamber not onlybalances the Earth and water pressure on the excavationsurface but also discharges the soil smoothly under thecontrol of a screw conveyor When the pressure chamber isnot filled with excavated soil and the pressure does not reachthe earth-water pressure on the excavation surface thetunneling state of the shield is between EPB mode and openmode which can be called a semiopen-mode EPB shieldconstruction

Although a semiopen-mode EPB shield construction cansolve the problem of blocking in a complex stratum there isno balanced relationship among the chamber pressureEarth pressure and water pressure of the stratum)ereforein addition to the potential instability of the excavationsurface and the risk of surface deformation the dischargingsystem and grouting system will also be affected In a per-meable stratum if the groundwater pressure is greater thanthe chamber pressure a large amount of groundwater willseep into the pressure chamber and affect the soil dischargeMeanwhile if the conventional grouting pressure behind thesegments is adopted grout leakage will occur in which thegrout behind the segments flows to the pressure chamber[20]

Some scholars have studied the construction perfor-mance and suitable driving mode of an EPB shield in dif-ferent strata According to the relationship between thepressure of the pressure chamber and the undergroundearth-water pressure on the excavation face the drivingmode of the EPB shield can be divided into four categoriesopen mode semiopen mode EPB mode and over-pressuremode James studied the construction parameters and cutterwear of an EPB shield and slurry shield when driving in thecomposite stratum of soil and weathered igneous rock [21])is research shows that when the proportion of rock on theexcavation section is more than 15 the average drivingspeed of the EPB shield is significantly reduced When theproportion of rock is more than 95 an open driving modeis appropriate In Hong Kong and Singapore some EPB

shield tunnels under the conditions of weathered igneousrock and a soil composite excavation face have adopted asemiopen mode to reduce the wear and torque under fullcabin construction In semiopen mode (also known as semi-EPB mode) there is no soil in the upper half of the pressuretank and the support pressure is provided by compressed air[22] When the air pressure of the upper part is less than theEarth and water pressure of the excavation face it is calledsemiopen under-pressure mode To date there have beenfew case studies on the construction of an EPB shield with asemiopen under-pressure in the literature

At present there is lack of systematic studies and en-gineering experience in the construction of an EPB shield inwater-rich weathered rock using semiopen mode Most ofthe shield tunnels of the R2 line of JinanMetro are located inwater-rich weathered diorite stratum )e groundwater isrich and the weathering degree of the rock stratum isuneven During the EPB shield tunneling many semiopenunder-pressure modes occurred as did the typical problemof a chamber soil sliming Regarding the occurrence of thisproblem and the formulation of proper solutions in thisstudy the parameters of the construction and discharged soilon the construction site and the seepage flow in the chamberare measured A theoretical analysis was conducted and theprinciple and control measures of chamber soil sliming arediscussed herein

2 Project Overview and Problems

21 Project Overview Jinan is the capital of ShandongProvince in China with a total area of 10244 km2 and apermanent population of 75 million as of 2018 Jinan is richin springs which has created challenges for the constructionof the metro lines )e layout of the Jinan Metro lines andthe distribution of the springs are shown in Figure 1 )efirst phase of Jinan Metro line R2 is an east-west urban lineconnecting the key areas of Jinan such as the Lashan areathe core area of the western new city the old urban area andthe high-tech zone It is a backbone rail transit line aiming torelieve the east-west traffic pressure and support the spatialexpansion of the strip city Phase I of the R2 line starts fromWangfuzhuang station in the west and ends at Pen-gjiazhuang station in the east with a total length of ap-proximately 36302 km including a 34502 km undergroundline a 1489 km elevated line and a 0311 km open section)e tunnel is expected to be officially opened to traffic by theend of 2020 )e interval tunnel is being constructed using afour-spoke panel composite-type EPB shield with a cutterhead opening rate of 40 As shown in Figure 2 the cutterhead excavation diameter is 668m and the device isequipped with 37 disc cutters and 48 scrapers )e basicparameters of the shield machine are listed in Table 1 )eburied depth of the tunnel is approximately 49ndash497m andthe geology along the tunnel is complex including com-pletely weathered diorite strongly weathered diorite andmoderately weathered diorite limestone silty clay gravellysoil and sandy-pebble stratum Among these strata thetunnel passes through the weathered diorite for the longest

2 Advances in Civil Engineering

distance which is more than 30 of the total length of theunderground line that is approximately 11 km

)e research object is a section of the R2 line of JinanMetro )e interval tunnel is 1003 km long with a depth of97ndash177m and the groundwater buried depth is approxi-mately 2m )e main strata traversed in the interval arecompletely weathered diorite strongly weathered dioriteand moderately weathered diorite )e strata profiles areshown in Figure 3 )e completely weathered diorite has ahigh degree of weathering and the strongly weathered di-orite has a good self-stability before excavation After beingdisturbed by the cutter head the strongly weathered dioriteforms soil particles similar to medium-coarse sand with alarge permeability coefficient and little cohesion )e

moderately weathered diorite has high strength and goodself-stability )e specific geological parameters are listed inTable 2

22EngineeringGeology )e geomorphic unit of the projecttunnel is piedmont alluvial plain )e terrain along thetunnel line is generally gentle and the ground elevation isbetween 2597 and 2679m with a maximum height dif-ference of approximately 082m )e strata involved in theproject are mainly Yanshanian intrusive gabbro diorite anda Cenozoic quaternary system

Diorite with different degrees of weathering is widelydistributed along the project Diorite contains mainly pla-gioclase quartz amphibole epidotes calcite pyrite andchloride [23] )e face of the completely weathered diorite isgrayish-yellow to grayish-green in color the original rockstructure has been destroyed and the core is mostly of a sandtype which is fragile when handled by hand )e face of thestrongly weathered diorite is grayish-green to grayish-yellowin color and the original rock has a clear medium-coarsegrain structure with the development of joint fissures Inaddition the core is mostly fragmentary with a short col-umn and occasionally a long column and is fragile fromhammering with a core recovery rate of 75ndash85 )emoderately weathered diorite is grayish-green with a me-dium-coarse grain structure is of a block type and hasslightly developed joint fissures A calcite dyke can be seen inthe moderately weathered diorite )e core is mostly co-lumnar with a length of 10ndash25 cm and the core recovery rateis 80ndash90 Meanwhile there are many completely tostrongly weathered soft intercalations in some parts ofmoderately weathered diorite

)e completely weathered and strongly weathered di-orite softens when encountering water and its strengthdecreases after saturation Some sections of the tunnel arelocated in structural fracture zones and rock layers withdifferent degrees of weathering Under the influence ofadverse factors such as groundwater action and construction

Figure 2 Cutter wheel of EPB shield used in Jinan Metro line R2

Table 1 Basic parameters of shield machine

Name Parameter UnitModel CTE6650H-0945

Project name Jinan Metro lineR2

Segment (ODID width) V 64005800sim1200 mm

Excavation diameter V 6680 mmCutter speed 0sim315 rpm

Maximum excavating speed asymp80 mmmin

Maximum thrust 4255 TTotal length of shield asymp85 mTotal length of main machine(excluding cutter head) 8389 mm

Maximum design pressure 5 barCutter head size (diameter length) V 6680 1645 mmCutter head opening rate 40 OD outer diameter ID internal diameter

China

Yellow River

Yangtze RiverJinan

Jinan

Beijing

N

SYellow River

White spring

Baimai spring

Jade river spring

Bubbling springCassock spring

Hongfanchi spring

0 20 40 Kilometers

Spring groupR2 lineOther metro lines

Figure 1 Location and general layout of Jinan Metro lines anddistribution of the main spring groups

Advances in Civil Engineering 3

disturbances adverse engineering phenomena such asseepage and a piping effect are easy to occur during theprocess of foundation pit construction and accidents such asa water inrush a mud outburst and collapse easily occurduring the construction of a connecting passage when themining method is used [24] which are also challenges to ashield construction method

23 Chamber Soil Sliming Phenomenon

231 Section State According to the construction of the R2line of Jinan Metro when the EPB shield tunnel passesthrough a full section of strongly weathered diorite or theupper section is strongly weathered diorite and the lowersection is moderately weathered diorite owing to the goodself-stability of the tunnel excavation face and the insensi-tivity of the surface settlement a semiopen under-pressuredriving mode is adopted When passing through theweathered diorite stratum the stratum permeability coef-ficient is approximately 10minus 5ms )e soil is in the form ofdebris after the cutter head excavation without cohesionand soil-water separation occurs

)e weathered rock is cut by the disc cutter to formcoarse and fine rock powder whereas the rich fissuregroundwater seeps into the chamber andmixes with the rockpowder to form a mud-like soil which is discharged using ascrew conveyor However because the discharged soil isalmost in a thin mud state the soil in the joint part of thescrew conveyor and the belt conveyor leaks and the cleaningof a large amount of thin mud-like soil at the bottom of thetunnel significantly reduces the construction efficiency )is

phenomenon can be called chamber soil sliming )e es-sential difference between soil sliming and spewing iswhether the pressure in the pressure tank is maintained ornot When the spew occurs the chamber is in a pressure-maintaining state and the higher chamber pressure acts onthe soil and pore water but when the chamber soil lacks thenecessary plastic flow state the pore water pressure in thesoil cannot be effectively dissipated during the process ofdischarge by the screw conveyor After the soil is disturbedthe water in the soil pore forms a concentrated seepagechannel and moves outward together with the soil particles)e mixture of soil and water originally discharged at thesame speed generates a relative movement When theseepage of water with a high-water pressure flows to theoutlet there is a large pressure difference with the externalatmospheric pressure resulting in a rapid outflow of water inthe soil and a driving of the transported soil causing spewing[10 11 25 26] )erefore spewing occurs under a fullchamber state the pressure in the chamber is relatively largeand the chamber soil is a mixture of soil and water with highfluidity However when soil sliming occurs there is nopressure-maintaining in the chamber the volume of soil inthe chamber is less and the pressure in the chamber is lowerGenerally the chamber pressure is slightly higher than thegravity pressure of the chamber soil and the undergroundwater pressure is greater than the chamber pressure A largeamount of underground water infiltrates into the chamberresulting in the mud-like soil Meanwhile the two condi-tions also have different impacts on the construction )espewing may cause the instability of the excavation surfacethe loss of groundwater and the surface settlement It can bealleviated by injecting bentonite slurry and other soil

Excavation direction0m

10m

20m

30m

A B

C

DE

ndash2m groundwater level

1003m

K11

+ 70

4

K12

+ 70

7

Figure 3 Geological section of a section of Jinan Metro line R2 A backfill soil B silty clay C completely weathered diorite D sandystrongly weathered diorite E moderately weathered diorite

Table 2 Geological parameters of the interval tunnel

Soil ρ (gcm3) w () wL () wP () Dry σc saturated (MPa) k (ms)

Backfill soil 178 221 mdash mdash mdash mdash mdashSilty clay 193 235 344 213 mdash mdash 325times10minus 8

Completely weathered diorite 196 209 274 188 mdash mdash 34times10minus 5

Sandy strongly weathered diorite 215 mdash mdash mdash 175 119 23times10minus 5

Moderately weathered diorite 231 mdash mdash mdash 583 486 mdashρ natural density w natural moisture content wL liquid limit wP plastic limit σc uniaxial compressive strength k hydraulic conductivity


conditioning additives into the chamber However soilsliming usually occurs in the stratum that can stand on itsown so it basically does not affect the stability of the ex-cavation surface Due to the small amount of soil in thechamber and the high moisture content of the chamber soilthe soil conditioning additives will be diluted by waterquickly after being added to the chamber making it difficultto control and solve the problem of chamber soil sliming in atimely manner

232 Construction Parameters )e self-stability of stronglyand moderately weathered diorite is high To improve theconstruction speed the construction workers adopted asemiopen under-pressure tunneling mode )e strata tra-versed by the EPB shield in the first 330 rings on the left lineof the tunnel in this area were mainly full-section highlyweathered diorite Under semiopen under-pressure tun-neling mode the average excavating speed of each ring was20ndash30mmmin with the maximum reaching 43mmminthe excavation time of each ring was approximately 08 h andthe average torque of each ring was approximately 3600 kN-m and the chamber soil could be normally dischargedWhen driving to the 330th ring moderately weathereddiorite invaded the lower part of the excavation sectionWhen driving to the 340ndash350th rings the speed was rapidlyreduced to 2mmmin Meanwhile as the strength of thestratum on the excavation surface increased the penetrationdegree of the cutter decreased and the torque was ap-proximately 2700 kN-m as shown in Figure 4 According tothe construction parameters of the left line shield machine inrings 300ndash350 the volume of the chamber soil accounted for13 to 12 of the volume of the pressure chamber and the topchamber pressure was 0 bar According to the buried depthof the tunnel the water pressure at the top of the excavationface was approximately 15 bar and hence no air pressurewas applied at the top to balance the soil and water pressureat the excavation face )e pressure in the middle andbottom of the pressure chamber is shown in Figure 5 whenthe EPB shield passed the 300ndash350th rings Because theexcavation face has a self-stability the lateral Earth pressureof the excavation face acting on the shield machine was notconsidered As can be seen from Figure 5 the groundwaterpressures in the middle and bottom of the excavation facewere approximately 176 and 21 bar respectively )echamber pressure in the construction process was signifi-cantly lower than the underground water pressure in thesection Under the action of the pressure difference betweenthe groundwater pressure and the chamber pressure as wellas a slow speed continuous seepage of the groundwater intothe pressure chamber occurred Meanwhile a compositestratum with an uneven strength may cause damage to thecutter to further understand the condition of the excavationface and cutter wear the EPB shield can be stopped and thechamber opened for inspection

233 Moisture Content of Discharged Soil To clarify thedegree of chamber soil sliming of Jinan Metro line R2 andprovide verification data for the subsequent calculation

moisture content tests were conducted on the soil samplestaken from the discharged soil pit at the construction siteand the outlet of the screw conveyor resulting in a moisturecontent of approximately 55ndash60 In addition the plasticlimit of the discharged soil wP was 169 and the liquidlimit wL was 215 )erefore the actual moisture contentof the discharged soil reached 26ndash28 wL )e dischargedsoil showed poor workability and occupied the site andunder a state of water and soil separation was difficult totransport out )e discharged soil at the construction site isshown in Figure 6

3 Measurement Method and CalculationModel of Water Seepage

31 Measured Section and Method To solve the problemregarding the amount of groundwater that will permeateinto the pressure chamber during the construction of eachring when the chamber is not full and under-pressure a fieldseepage test was conducted )e seepage amount of thetunnel in this area was measured at the open section of the350th ring of the left line )e measured cross sectionstratum comprised strongly weathered diorite in the upperpart and moderately weathered diorite in the lower partwith good self-stability of the excavation surface and richfissure water as shown in Figure 7 )e buried depth of thissection was approximately 162m the groundwater was 2mand the permeability coefficient was approximately 10minus 5ms

Owing to the high self-stability of the excavation surfacea method for opening the chamber under normal pressurewas adopted in this project After the soil in the chamber wasdischarged completely the construction personnel couldopen the pressure chamber and enter the chamber for aremovable cutter-changing operation However to safelyand conveniently observe the change in the water level in thechamber the height of the controlled chamber soil waslocated near the central cutter that is the height of the soil inthe chamber was 12 the height of the pressure chamber andthe soil was in a saturated state Under a different water headthe continuous infiltration of groundwater will cause a risein the water level of the chamber )e measurement per-sonnel observed the source of water seepage in the man lockand recorded the difference in the water level in the chamberevery hour According to the difference in the water level thewater seepage from the stratum to the chamber could beobtained Considering the relatively large permeability co-efficient a long measurement time a large amount of waterseepage and the safety of the measured personnel when thewater level was close to the bottom plate of the man lock thewater pump was used to pump out the excess water in thechamber until the top of the chamber soil was exposed andthe rise of the water level was then recorded again)e abovesteps were repeated until the measurement time reached 4 h

32 Principle of the Seepage Calculation Model Under asemiopen under-pressure condition in addition to theseepage from the excavation surface into the chamber alarge amount of water seepage occurred in the gap between


the shield shell and the surrounding rock )is is probablydue to the existence of an overbreak in the relatively hardweathered rock the tunneling diameter is slightly larger thanthe shield diameter and thus a gap between the shield andstratum appears Because the surrounding rock has goodself-stability a gap can occur from the cutter head to the tailof the shield Around the tail of the shield owing to thefilling effect of grout behind the segment the gap mightdisappear During tunneling in addition to synchronousgrouting of the gap at the tail of the shield secondarygrouting was also conducted through the grouting holes onthe segments and thus it can be considered that there was nogroundwater seepage around the segment rings after theshield tail [27 28] When establishing the water seepage

model it was assumed that the chamber soil was saturatedand the excavation surface and surrounding rock of the shieldwere considered as the groundwater seepage surfaces )egroundwater head and permeability coefficient of the sur-rounding rock as well as the water head in the chamber soilwere the boundary conditions of the seepage )e excavationspeed of the tunnel affected the time of groundwater seepageinto the chamber during the construction of each ring

4 Results

41 Measured Water Seepage According to the abovemeasurement method the volume of groundwater seepageinto the chamber was calculated based on the change in the

310 330 340 350300 320Ring number

00

04

08

12

16

20

Pres

sure

(bar

)

pcndashmpwndashm

(a)

310 330 340320 350300Ring number

00

04

08

12

16

20

24

Pres

sure

(bar

)

pcndashbpwndashb

(b)

Figure 5 Chamber pressure of the shield and water pressure of excavation surface wheel at 300ndash350 rings pcminus m is the pressure in the middleof the pressure chamber pwminus m is the water pressure in the middle of the excavation surface pcminus b is the pressure at the bottom of the pressurechamber and pwminus m is the water pressure at the bottom of the excavation surface

60

40

20

0

Exca

vatio

n sp

eed

(mm

min

)

300 310 320 330 340 350Ring number

6000

5000

4000

3000

2000

1000

0

Cutti

ng to

rque

(kN

m)

Strongly and moderatelyweathered dioriteStrongly weathered diorite

Excavation speedAverage speed

Cutting torqueAverage torque

Figure 4 Monitoring results of excavation speed and cutting wheel torque at 300ndash350 rings


water level in the chamber within a certain time )e tunneladopted synchronous grouting and secondary groutingbehind the segments and applied a C-S grout to form a waterstop hoop between the segment rings and the stratum everyfive rings)us it can be considered that there was less waterseepage in the chamber behind the shield tail According tothe observation in the man lock the groundwater seepageinto the chamber was mainly the fissure water of the tunnelexcavation surface and the stratum around the shieldparticularly the latter )e measured value of water seepagefrom the stratum to the chamber is shown in Figure 8 Asshown here after 05 3 and 4 h volumes of 38 228 and304m3 of groundwater seeped into the pressure chamberrespectively

42 Seepage Model and Calculation Results

421 Calculation Model and Parameters Based on Darcyrsquoslaw and taking a certain section of the R2 line of the JinanMetro as the prototype a calculation model of the sur-rounding rock groundwater seepage into the chamber wasestablished a model diagram of which is shown in Figure 9In the model H and Hw are the tunnel and groundwater

depths respectively hw is the groundwater head at the topof the tunnel α is the water head coefficient in the chamberwhich refers to the ratio of the water head height in thechamber and the tunnel diameter αD and D are the waterhead height in the chamber and the tunnel diameter re-spectively and L is the shield length It can be seen fromFigure 9 that the groundwater head at the bottom of thetunnel excavation face is hw +D whereas the water head atthe bottom of the pressure chamber is αD )ere is a waterhead difference Δh between the bottom of the excavationface and the bottom of the pressure chamber under whichthe groundwater will gradually seep into the pressurechamber )e model is suitable for the water-rich stratumwith good self-stability and no obvious difference of per-meability coefficient between the excavation face and thestratum along the direction of shield cylinder )e stratumused in the calculation model was weathered diorite whichwas similar to medium-coarse sand with little cohesion

(a) (b)

Figure 6 Discharged soil at the construction site

Figure 7 Excavation surface condition during field seepagemeasurement

Wat

er se

epag

e (m

3 )

25 30200500 10 35 40 4515Time (h)

0

5

10

15

20

25

30

35

Measured value

Figure 8 Measured value of water seepage


after excavation)e permeability coefficient of the stratumwas approximately 10minus 5ms and the buried depths of thistunnel section and the groundwater were 162 and 2mrespectively )e initial water content of the stratum was20 the excavation diameter was 668m the shield lengthwas 8389m the excavation time was 4 hring and thesegment width was 12m )e chamber soil volumeaccounted for 12 of the chamber volume and the waterlevel in the chamber was the same as the height of thechamber soil

422 Calculation of Seepage from the Stratum around theShield During the excavation in semiopen mode the waterseepage around the shield was divided into parts A and B asshown in Figure 9 )ere are differences in the hydraulicgradients between the part without chamber soil part A andthat with chamber soil part B during the seepage process)e hydraulic gradient of part A is 1 whereas the hydraulicgradient of part B is related to the location of the selectedcalculation unit

As shown in Figure 9 the length of the shield is L and thewater seepage from the stratum around the shield in part A isas follows

iSA 1

QSA kiSAASAt(1)

To simplify the calculation the hydraulic gradient of thesoil element in the middle of the chamber soil was obtainedto calculate the water seepage from the stratum around theshield in part B which is expressed as follows

iSB hw +(1 minus α)d

hw +(1 minus α2)d

QSB kiSBASBt

(2)

where i is the hydraulic gradient referring to the ratio ofhead loss along the seepage path to the length of the seepagepathQS is the water seepage of the stratum around the shieldfor a certain period of time m3 hw is the groundwater headat the top of the tunnel m α is the coefficient of the waterhead in the chamber referring to the ratio of the height ofthe water head in the pressure chamber to the diameter ofthe tunnel d is the tunnel diameter m k is the permeabilitycoefficient of the stratum ms A is the seepage area m2 andt is the seepage time h

423 Calculation of Seepage on the Excavation SurfaceUnder the condition of semiopen under-pressure drivingmode the water seepage on the excavation surface is alsocomprised of two parts

)e seepage volume of part A of the excavation surface isas follows

iFA 1

QFA kiFAAFAt(3)

)e center of the tunnel was taken as the origin of thecoordinate axis as shown in Figure 9 )e calculation unitwas selected and integrated along the height of the chambersoil and the calculation formulas of the seepage volume ofpart B of the excavation surface were obtained as follows

Water levelin chamber

Ground level

Hhw

Hw

Air

Chamber soil

DαD

A

B

L

Groundwaterlevel

(a)

A

B

y

D

xdy

(b)

Figure 9 Schematic of the seepage model


QFB 2kt 1113946(αminus (12))d

minus (d2)

hw +(1 minus α)d

hw +(d2) minus y

d2

4minus y

2

1113971

dy

QFB 2kt hw +(1 minus α)d1113858 1113859

minush2

w + hwd1113968

arcsin2hw(α minus (12)) + d(α minus 1)

(α minus 1)d minus hw

11138681113868111386811138681113868111386811138681113868

1113890 1113891

+ hw +d

21113888 1113889arcsin(2α minus 1) minus d

α(1 minus α)

1113968+ 157 hw +

d

2minus

h2w + hwd

1113969

1113888 1113889

⎧⎪⎪⎪⎪⎪⎪⎪⎨

⎪⎪⎪⎪⎪⎪⎪⎩

⎫⎪⎪⎪⎪⎪⎪⎪⎬

⎪⎪⎪⎪⎪⎪⎪⎭

(4)

where QF is the seepage volume of the excavation surfacestratum within a certain period of time m3

424 Calculation Results of Water Seepage According tothe specific stratum permeability coefficient excavationspeed groundwater head and chamber soil height theseepage volume of the tunnel excavation face and shieldsurrounding the stratum to the chamber can be obtainedand the variation of the water content of the chamber soilduring the seepage process can then be calculated accordingto the excavation soil volume of each ring and the initialwater content of the chamber soil

Based on the above measured water seepage from theexcavation surface and the surrounding stratum of the shieldto the chamber the calculated value of the model wascompared with the measured value as shown in Figure 10Here it can be seen that the established seepage calculationmodel has good accuracy Because the shield at the selectedsection was in a downhill state more water might flow to thechamber under the action of gravity however the influenceof the shield angle was not considered in the calculationmodel and thus the measured value will be slightly largerthan the calculated value )rough the field test it wasobserved that a large amount of groundwater in the chambercomes from the gap between the shield cylinder and thestratum In the construction the water stop hoops betweenthe segments and the stratum were provided every 5 ringswhich can effectively limit the seepage caused by no so-lidification of grouting behind the segments However theimpermeability of the newly injected grouting is poor whenit is not solidified so it is indeed possible to have a smallamount of seepage But when establishing the calculationmodel it was assumed that there will be no water seepagebehind the shield tail due to the existence of grouting )elength of the water seepage path along the direction of theshield cylinder was taken as the length of the cylinder andthe consistency between the calculation results and themeasured results is good )erefore it is considered that thewater seepage near the newly assembled segments can beignored and the groundwater seepage along the shieldcylinder ends at the shield tail Overall the calculationmodelof seepage can accurately reflect the actual situation

43 Influence Law and Sensitivity Analysis of Each Parameteron Moisture Content of Chamber Soil )e high water con-tent of the chamber soil is one of the characteristics of the

phenomenon of chamber soil sliming To clarify the influ-ence rule and occurrence condition of the relevant factors ofthis phenomenon the water seepage volume was convertedinto the water content of the chamber soil for furtheranalysis )e water head in the chamber excavation timepermeability coefficient and groundwater head are im-portant factors affecting the water content of the chambersoil and the value range of each parameter is listed inTable 3 )e EPB tunneling mode is an ideal constructionmode that is the chamber pressure is balanced with theearth-water pressure of the excavation face and the water inthe stratum will not seep into the chamber and thus the EPBmode was not considered in this study When the chamberwas in semiopen under-pressure mode the water pressure inthe chamber was calculated separately )e height of thewater level in the chamber was the same as the height of thechamber soil

)e influence rules of the water head in the chamber theexcavation time the permeability coefficient and thegroundwater head on the moisture content of the dischargedsoil are shown in Figures 11ndash14 respectively Figure 11shows that the water head in the chamber is negativelycorrelated with the moisture content of the discharged soilIncreasing the height of the chamber soil was conducive toreducing the seepage of groundwater into the pressurechamber It can be seen from Figure 12 that whenk 10minus 5ms and α 23 the moisture content of the dis-charged soil increased significantly with an increase in theexcavation time Figure 13 shows that the moisture contentcurve of the discharged soil turned when the permeabilitycoefficient k was 10minus 6ms when k increased from 10minus 7 to10minus 6ms the discharged soil moisture content increasedslowly whereas when k increased from 10minus 6 to 10minus 5ms thedischarged soil moisture content increased rapidly Asshown in Figure 14 with an increase in the groundwaterhead the moisture content of the discharged soil slightlyincreased and with a decrease of the water head coefficientin the chamber the influence of the groundwater head onthe moisture content of the discharged soil decreased

To propose effective prevention and control measuresagainst the phenomenon of chamber soil sliming the keyfactors affecting this phenomenon must first be clarified)erefore a sensitivity analysis method was used to analyzethe correlation between the relevant parameters and themoisture content of the discharged soil Meanwhile througha sensitivity analysis the main and secondary influenceparameters of chamber soil sliming can be determined


which is helpful when proposing control measures )e firststep of the sensitivity analysis method was to establish ananalysis system model [29] that is the functional rela-tionship between the system characteristic P and factorsx1 x2 xn for example P f (x1 x2 xn) )e sec-ond step was to provide the benchmark parameter setaccording to the specific problems to be analyzed )ebenchmark value and range of variation of each parameter

selected in this study are listed in Table 4 and the sensitivityof each parameter was then calculated according to thefollowing equation

Sk |ΔPP|

ΔXkXk

11138681113868111386811138681113868111386811138681113868

ΔPΔXk

11138681113868111386811138681113868111386811138681113868

11138681113868111386811138681113868111386811138681113868

Xk

P

1113868111386811138681113868111386811138681113868

1113868111386811138681113868111386811138681113868 (5)

where Sk is the sensitivity of factor xk where k 1 2 n|ΔPP| is the relative change rate of the system character-istics and |ΔXkXk| is the relative change rate of a certainfactor

Only one factor is changed in each calculation and otherfactors remain unchanged )e sensitivity of each factor isanalyzed individually the results of which are listed in

60

62

64

66

68

Moi

sture

cont

ent o

f disc

harg

ed so

il (

)

035 040 045 050 055 060 065 070030α

hw = 7mhw = 10m

hw = 13mhw = 16m

Slight sliming

Serious sliming

Figure 11 Influence of α on the moisture content of chamber soilwhen k 10minus 5ms and t 4 hring

3530 4005 2510 4500 15 20Time (h)

Wat

er se

epag

e (m

3 )

0

5

10

15

20

25

30

35

Calculated valueMeasured value

Figure 10 Measured and calculated values of the water seepagevolume

Table 3 Seepage model parameters

α t (hring) k (ms) hw (m)

23 12 13 4 6 8 10minus 5 10minus 6 10minus 7 7 10 13 16

4 6 820Excavation time t (hring)

20

40

60

80

100

120

Moi

sture

cont

ent o

f disc

harg

ed so

il (

)

hw = 7mhw = 10m

hw = 13mhw = 16m

Serious sliming

Slight sliming

Normal

Figure 12 Influence of t on the moisture content of chamber soilwhen k 10minus 5ms and α 23

Permeability coefficient k (ms)

Serious sliming

Slight sliming

Normal

10

20

30

40

50

60

70

Moi

sture

cont

ent o

f disc

harg

ed so

il (

)

1E ndash 07 1E ndash 06 1E ndash 05

hw = 7mhw = 10m

hw = 13mhw = 16m

Figure 13 Influence of k on the moisture content of chamber soilwhen t 4 hring and α 23


Table 5 Here it can be seen that among the four selectedparameters the moisture content of the discharged soil hasthe highest sensitivity to the excavating time t followed bythe permeability coefficient k and water head coefficient inthe chamber α and the relationship between the moisturecontent of the discharged soil and groundwater head hwwas the furthest )erefore in the process of constructionthe most effective measure used to control the phenomenonof chamber soil sliming is to shorten the excavation time andreduce the permeability coefficient of the chamber soil bymeans of soil conditioning

44 Occurrence Conditions and Critical Values Combinedwith the above research and engineering measured data thepossibility of chamber soil sliming under semiopen under-pressure mode was evaluated based on the permeabilitycoefficient the pressure difference between the excavationsurface water pressure and chamber pressure P and theexcavation time After the weathered diorite was excavatedthe liquid limit of the discharged soil wL was approximately215 Combined with the moisture content of the dis-charged soil on site it was considered that when themoisture content of the chamber soil w is 2wL lewle 3wLslight chamber soil sliming may occur whereas whenwge 3wL serious chamber soil sliming may occur )us thecritical condition for the occurrence of chamber soil slimingis as shown in Figure 15

According to the establishedmodel when the excavationtime was 4 hring and the permeability coefficient was

kge 5times10minus 6ms chamber soil sliming may occur and whenkge 1times 10minus 5ms this phenomenon is more serious )elonger the excavation time the lower the permeability co-efficient required for sliming to occur When the advancingtime was 6 hring and kge 4times10minus 6ms chamber soil slimingwill occur and when kge 7times10minus 6ms more serious slimingmay occur )erefore with an increase in the advancingtime the range of formation permeability coefficient whichmay cause serious chamber soil sliming clearly increases

5 Discussion

51 Comparison of the Critical Conditions of Sliming andSpewing of Chamber Soil )e difference and connectionbetween the sliming and spewing of the chamber soil aredescribed above )e sliming of the chamber soil was ex-cavated under the condition of a nonfull chamber and lowchamber pressure and a large amount of groundwaterseepage into the chamber resulting in a thin mud state ofchamber soil close to the liquid phase Under the conditionof tunneling with a full chamber and high chamber pressurethere was a large pressure difference between the waterpressure in the chamber and the atmospheric pressure at thescrew conveyor outlet which results in a spewing of amixture of soil and water in the chamber In both cases themoisture content of the discharged soil was higher thus itwas easily confused during the construction processHowever the moisture content of the discharge soil duringsliming was generally higher than that during the spewing

)e critical conditions of the spewing phenomenon havebeen studied by scholars [10 11] Zheng et al considered thewater pressure of the screw conveyor outlet and ground-water flow as the spewing conditions and calculated therange of the groundwater pressure at the center of the ex-cavation surface and the permeability coefficient of thechamber soil when the spewing occurred [10] )egroundwater head and permeability coefficient of the projectwere introduced under the critical condition of spewing byZheng et al [10] who concluded that serious gushing willoccur However based on the observation of the discharge ofsoil during the site construction it was found that the soilwas not spewed from the outlet As the reason for thisdifference the excavation surface strength of the project washigh the semiopen under-pressure mode was adopted by theconstruction personnel and the chamber pressure wasrelatively low

As shown in Figure 15 the stratum permeability coef-ficient and the pressure difference between the excavationsurface water pressure and the chamber pressure were usedto analyze the critical conditions for the occurrence ofchamber soil sliming under different excavation speedsCompared with the above critical conditions of spewing the

Table 5 Sensitivity of moisture content of discharged soil to eachparameter

Parameter hw (m) α t (hring) k (ms)

Sensitivity 0056 0113 0769 0692

Serious sliming

Slight sliming

60

62

64

66

68

70M

oistu

re co

nten

t of d

ischa

rged

soil

()

10 16141286Groundwater head hw (m)

α = 13α = 12α = 23

Figure 14 Influence of hw on the moisture content of chamber soilwhen t 4 hring and k 10minus 5ms

Table 4 Reference value and change range of each parameter

Parameter hw (m) A t (hring) k (ms)

Benchmark value 16 12 4 10ndash5

Variation range 7sim16 13sim23 4sim8 10minus 7sim10minus 5


influence of the construction time was also consideredTaking this project as an example the permeability coeffi-cient of the stratum was approximately 1times 10minus 5ms sem-iopen under-pressure mode was used for driving and no soilconditioning additive was used to improve the plastic flow ofthe chamber soil )e project passed through completelyweathered diorite or strongly weathered diorite strata in thefull section in the first 330 rings It can be seen from Figure 4that the excavation speed was relatively fast namely ap-proximately 08 h for each ring without the occurrence ofchamber soil sliming However at the 340ndash350th rings theinvasion of the moderately weathered diorite with highstrength resulted in a time of approximately 10 h for eachring excavation It can be seen from Figure 5 that the dif-ference between the excavation surface water pressure andchamber pressure in the actual project was approximately50ndash60 kPa )erefore according to the critical conditions inFigure 15 serious soil sliming probably occurred in the340ndash350th rings indicating that the moisture content of

discharged soil is wge 3wL whereas the measured watercontent of the discharged soil on site is 26ndash28wL whichshows some errors )is analysis result might be due to thefact that the water separated from the discharged soil in-evitably causes part of the water to be lost from the soilsample when the soil sample is taken from the dischargeoutlet and the discharged soil pit which results in themeasured water content of the soil being less than thecalculated value In addition the calculation model sim-plifies the seepage process of groundwater which also leadsto a difference between the calculated and measured values

To summarize the critical condition indexes of thechamber soil sliming and spewing are similar with bothconsidering the groundwater pressure and the permeabilitycoefficient of the stratum and the results are close to those ofthe actual project It is easy to confuse the phenomena ofsliming and spewing of the chamber soil When judgingwhether these two phenomena will occur the shield ma-chine driving mode stratum parameters chamber pressure

0

10

20

30

40

50

60Pr

essu

re d

iffer

ence

P (k

Pa)

Permeability coefficient k (ms)1E ndash 06 1E ndash 05

t = 4hring

Normal Slightsliming

Serioussliming

(a)

0

10

20

30

40

50

60

Pres

sure

diff

eren

ce P

(kPa

)


t = 6hring


Serioussliming

(b)

0

10

20

30

40

50

60

Pres

sure

diff

eren

ce P

(kPa

)


t = 8hring

NormalSlight

slimingSerioussliming

(c)

Figure 15 Critical condition of the sliming phenomenon of chamber soil


groundwater pressure and excavation time should becomprehensively considered

52 Prevention Measures of Chamber Soil SlimingAccording to the results in Figures 11ndash14 and Table 5 themost effective measure used to avoid chamber soil sliming isto control the excavation time and the permeability coef-ficient of the chamber soil during the construction

Combined with the above research a semiopen under-pressure mode is most suitable for stratum with highstrength and low water amount When excavating inweathered stratum with a large amount of water a largepermeability coefficient and high strength this mode canalso be used to reduce the thrust and the wear of the cutterhead and improve the construction speed Here the ex-cavation time should be strictly controlled to avoid thephenomenon of sliming caused by excessive groundwaterseepage into the pressure chamber Taking the project asan example the stratum permeability coefficient was1 times 10minus 5 ms and the groundwater head was 7ndash16m if noconditioning measures are taken for the soil in thechamber the chamber soil volume should be controlled toaccount for at least 23 of the chamber volume and theexcavation time should not exceed 2 hring

)e shield machine used in the project was a four-spokepanel composite EPB shield the cutting capacity of whichwas significantly reduced when encountering moderatelyweathered diorite in addition the speed was limited whichresulted in a large amount of groundwater seepage into thepressure chamber and the soil in the chamber could not besmoothly discharged A large amount of thin mud-likechamber soil leaked into the bottom of the tunnel whichaffected the working environment and segment assembly Ittook a long time for the construction personnel to clean upthe soil with a high moisture content which further limitedthe construction speed More groundwater then seepedinto the chamber creating a vicious cycle )us when thespeed cannot be increased a low chamber soil heightshould be avoided According to this study the chambersoil height should be kept at 23 or more of the pressurechamber height and the soil conditioning measures shouldbe taken so the chamber soil forms a plastic flow state witha permeability coefficient of less than 1times 10minus 6 ms to bal-ance the groundwater and Earth pressure on the excavationsurface and prevent the groundwater seepage into thepressure chamber In the case of a dense formation andgood airproof capability the method of applying airpressure to the upper half of the pressure chamber can alsobe adopted simultaneously Maintaining an air pressureslightly higher than the groundwater pressure in the upperhalf of the chamber can prevent a large amount ofgroundwater seepage In addition through an observationof the situation occurring in the chamber it was found thatthe stratum around the shield and the excavation surfacewill seep into the chamber and the seeping water mainlycomes from the stratum around the shield )ereforeduring the process of shield machine propulsion measurescan be taken to inject waterproof materials into the gap

between the shield body and stratum such as bentoniteslurry with a high density and viscosity reducing the waterseepage around the shield

6 Conclusions

(1) Chamber soil sliming is a phenomenon in whichchamber soil is in a thin mud state with no pressurebalance in the pressure chamber of the EPB shieldand an excessive water content of the chamber soilowing to the continuous seepage of groundwaterinto the chamber in addition the chamber pressureis relatively low which is different from the phe-nomenon of spewing when the chamber pressure isrelatively high

(2) Based on the field measurement a large amount ofwater seepage from the stratum around the tunnelexcavation surface and shield to the chamber is asignificant factor leading to chamber soil slimingduring the construction process Considering theinfluence of the water head in the chamber theexcavation time the permeability coefficient of thestratum and the groundwater head a calculationmodel of water seepage was established which canbe used to calculate the change law of the waterseepage volume and the moisture content of thechamber soil )e field-measured and calculatedvalues of the water seepage were verified and it isconsidered that the calculation model of the waterseepage conforms relatively well to actual engi-neering practice

(3) )e influence of each parameter on the moisturecontent of the chamber soil and the sensitivity be-tween each parameter and the phenomenon ofchamber soil sliming were analyzed On this basisthe critical conditions for the occurrence of slimingwere divided and the relations and differences be-tween the critical conditions of sliming and thespewing phenomena were discussed

(4) Regarding the phenomenon of chamber soil slimingseveral preventative measures were proposed Whenthe EPB shield is used for tunneling in water-richweathered rock stratum with high permeability andhigh strength semiopen under-pressure excavatingmode can be used However to avoid excessive waterseepage in the chamber control of the excavationtime is recommended to be within 2 hring Whenthe speed cannot be increased for some objectivereasons the chamber soil height should be kept at 23or more of the pressure chamber height and soilconditioning measures should be taken such that thesoil forms a plastic flow In addition the applicationof air pressure to the upper part of the chamberwithout soil or the injection of a thick slurry andother waterproof materials into the gap between theshield shell and the stratum during the excavationcan be considered to prevent the occurrence ofsliming


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 they have no conflicts of interest

Acknowledgments

)is research was supported by the National Program onKey Basic Research Project of China (973 Program)(2015CB057803)

References

[1] R K Goel J L Jethwa and A G Paithankar ldquoTunnellingthrough the young Himalayasmdasha case history of the Maneri-Uttarkashi power tunnelrdquo Engineering Geology vol 39 no 1-2 pp 31ndash44 1995

[2] G-H Zhang Y-Y Jiao and H Wang ldquoOutstanding issues inexcavation of deep and long rock tunnels a case studyrdquoCanadian Geotechnical Journal vol 51 no 9 pp 984ndash9942014

[3] G-H Zhang Y-Y Jiao C-X Ma H Wang L-B Chen andZ-C Tang ldquoAlteration characteristics of granite contact zoneand treatment measures for inrush hazards during tunnelconstructionmdasha case studyrdquo Engineering Geology vol 235no 9 pp 64ndash80 2018

[4] S S Lv W Liu S H Zhai and P S Chen ldquoInfluence of waterinrush from excavation surface on the stress and deformationof tunnel-forming structure at the launching-arrival stage ofsubway shieldrdquo Advances in Civil Engineering vol 2019Article ID 6989730 20 pages 2019

[5] W C Cheng G Li A Zhou and J Xu ldquoRethinking the waterleak incident of tunnel Luo09 to prepare for a challengingfuturerdquo Advances in Civil Engineering vol 2019 Article ID4695987 11 pages 2019

[6] N Bilgin and M Algan ldquo)e performance of a TBM in asqueezing ground at Uluabat Turkeyrdquo Tunnelling and Un-derground Space Technology vol 32 pp 58ndash65 2012

[7] E Avunduk and H Copur ldquoEmpirical modeling for pre-dicting excavation performance of EPB TBM based on soilpropertiesrdquo Tunnelling and Underground Space Technologyvol 71 pp 340ndash353 2018

[8] K Bappler and W Burger ldquoInnovation track of multi-modemachines for complex ground conditionsrdquo in Proceedings ofthe Swiss Tunnel Congress pp 122ndash129 San Francisco CAUSA April 2016

[9] C Budach andM)ewes ldquoApplication ranges of EPB shieldsin coarse ground based on laboratory researchrdquo Tunnellingand Underground Space Technology vol 50 pp 296ndash3042015

[10] G Zheng X Dai and Y Diao ldquoParameter analysis of waterflow during EPBS tunnelling and an evaluation method ofspewing failure based on a simplified modelrdquo EngineeringFailure Analysis vol 58 pp 96ndash112 2015

[11] W Zhu J S Qin and K L Wei ldquoResearch on the mech-anism of the spewing in the EPB shield tunnelingrdquo ChineseJournal of Geotechnical Engineering vol 26 no 5pp 589ndash593 2004

[12] N Zhang J S Shen A Zhou and A Arulrajah ldquoTun-neling induced geohazards in mylonitic rock faults with

rich groundwater a case study in Guangzhourdquo Tunnellingand Underground Space Technology vol 74 pp 262ndash2722018

[13] S MWang X X Lu X MWang et al ldquoSoil improvement ofEPBS construction in high water pressure and high perme-ability sand stratumrdquo Advances in Civil Engineering vol 2019Article ID 4503219 9 pages 2019

[14] X Y Ye S YWang J S Yang D C Sheng and C Xiao ldquoSoilconditioning for EPB shield tunneling in argillaceous siltstonewith high content of clay minerals case studyrdquo InternationalJournal of Geomechanics vol 17 no 4 Article ID 050160022016

[15] P Liu S Wang L Ge M )ewes J Yang and Y XialdquoChanges of Atterberg limits and electrochemical behaviors ofclays with dispersants as conditioning agents for EPB shieldtunnellingrdquo Tunnelling and Underground Space Technologyvol 73 pp 244ndash251 2018

[16] D G G de Oliveira M )ewes and M S DiederichsldquoClogging and flow assessment of cohesive soils for EPBtunnelling proposed laboratory tests for soil characteriza-tionrdquo Tunnelling and Underground Space Technology vol 94Article ID 103110 2019

[17] H H Zhu C Panpan Z Xiaoying L Yuanhai and L PeinanldquoAssessment and structural improvement on the performanceof soil chamber system of EPB shield assisted with DEMmodelingrdquo Tunnelling and Underground Space Technologyvol 96 Article ID 103092 2020

[18] G Carrieri E Fornari V Guglielmetti and R Crova ldquoTorinometro line 1 use of three TBM-EPBs in very coarse grainedsoil conditionsrdquo Tunnelling and Underground Space Tech-nology vol 21 no 3-4 pp 274-275 2006

[19] H Jiang Y S Jiang M L Huang and X Nie ldquoStudy on soilconditioning and key construction parameters of EPB TBMadvancing in sand-pebble layer of Beijing metrordquo AppliedMechanics and Materials vol 90ndash93 pp 2138ndash2142 2011

[20] F Ye Z Chen C H Sun et al ldquoPenetration diffusion modelfor backfill grouting through segments of shield tunnelconsidering weight of groutrdquo Chinese Journal of GeotechnicalEngineering vol 38 no 12 pp 2175ndash2183 2016

[21] J N Shirlaw ldquoPressurised TBM tunnelling in mixed faceconditions resulting from tropical weathering of igneousrockrdquo Tunnelling and Underground Space Technology vol 57pp 225ndash240 2016

[22] Anon GEO Report 298 Ground Control for EPB TBM Tun-nelling Prepared by the Geotechnical Engineering OfficeHong Kong China 2014

[23] H Basarir ldquoEngineering geological studies and tunnel sup-port design at Sulakyurt dam site Turkeyrdquo Engineering Ge-ology vol 86 no 4 pp 225ndash237 2006

[24] S Dalgic ldquoTunneling in squeezing rock the Bolu tunnelAnatolian motorway Turkeyrdquo Engineering Geology vol 67no 1-2 pp 73ndash96 2002

[25] D Peila ldquoSoil conditioning for EPB shield tunnellingrdquo KSCEJournal of Civil Engineering vol 18 no 3 pp 831ndash836 2014

[26] Z P Zhu Study on Anti-blowout Induced by EPB ShieldTunneling under High Water Pressure in Sandy Cobble Stra-tum Beijing Jiaotong University Beijing China 2016 inChinese

[27] X Li L Wang M Hao Y Zhong and B Zhang ldquoAn an-alytical solution for the radial flow of variable density grout inrock fracturesrdquo Construction and Building Materials vol 206pp 630ndash640 2019

[28] X L Liu FWang J Huang et al ldquoGrout diffusion in silty finesand stratum with high groundwater level for tunnel


constructionrdquo Tunnelling and Underground Space Technologyvol 93 Article ID 103051 2019

[29] G Zhang and W S Zhu ldquoParameter sensitivity analysis andtest scheme optimizationrdquo Rock and Soil Mechanics vol 14no 1 pp 53ndash60 1993 in Chinese


the construction with a nonfull chamber is generallyadopted which will not affect the stability of the excavationsurface at the same time a faster construction speed can beobtained under a smaller thrust and torque and the re-quirements for the chamber soil conditioning are relativelysimple )erefore the construction of semiopen under-pressure mode is common in projects )is type of situationoften occurs in a soft rock stratum which can stand aloneand remain stable as well as in medium-coarse sand and asandy-pebble stratum Under this situation it is difficult toform a plastic flow in the chamber soil )e soil in the plasticflow state is paste-like the permeability coefficient of the soilis less than 10minus 5ms the slump is 150ndash200mm and the highcompressibility usually requires a volume compression rateof at least 2 and low shear strength [9] Owing to thedifficulty in forming a plastic flow of soil in a pressurechamber an EPB shield is prone to spewing [10ndash13]blocking and cake formation [14ndash19] as well as otherphenomena during the construction of such strata )e EPBshield originates from the construction of a soft clay stratumwhich easily forms a plastic flow after being disturbed in thepressure chamber )e soil in the pressure chamber not onlybalances the Earth and water pressure on the excavationsurface but also discharges the soil smoothly under thecontrol of a screw conveyor When the pressure chamber isnot filled with excavated soil and the pressure does not reachthe earth-water pressure on the excavation surface thetunneling state of the shield is between EPB mode and openmode which can be called a semiopen-mode EPB shieldconstruction

Although a semiopen-mode EPB shield construction cansolve the problem of blocking in a complex stratum there isno balanced relationship among the chamber pressureEarth pressure and water pressure of the stratum)ereforein addition to the potential instability of the excavationsurface and the risk of surface deformation the dischargingsystem and grouting system will also be affected In a per-meable stratum if the groundwater pressure is greater thanthe chamber pressure a large amount of groundwater willseep into the pressure chamber and affect the soil dischargeMeanwhile if the conventional grouting pressure behind thesegments is adopted grout leakage will occur in which thegrout behind the segments flows to the pressure chamber[20]

Some scholars have studied the construction perfor-mance and suitable driving mode of an EPB shield in dif-ferent strata According to the relationship between thepressure of the pressure chamber and the undergroundearth-water pressure on the excavation face the drivingmode of the EPB shield can be divided into four categoriesopen mode semiopen mode EPB mode and over-pressuremode James studied the construction parameters and cutterwear of an EPB shield and slurry shield when driving in thecomposite stratum of soil and weathered igneous rock [21])is research shows that when the proportion of rock on theexcavation section is more than 15 the average drivingspeed of the EPB shield is significantly reduced When theproportion of rock is more than 95 an open driving modeis appropriate In Hong Kong and Singapore some EPB

shield tunnels under the conditions of weathered igneousrock and a soil composite excavation face have adopted asemiopen mode to reduce the wear and torque under fullcabin construction In semiopen mode (also known as semi-EPB mode) there is no soil in the upper half of the pressuretank and the support pressure is provided by compressed air[22] When the air pressure of the upper part is less than theEarth and water pressure of the excavation face it is calledsemiopen under-pressure mode To date there have beenfew case studies on the construction of an EPB shield with asemiopen under-pressure in the literature

At present there is lack of systematic studies and en-gineering experience in the construction of an EPB shield inwater-rich weathered rock using semiopen mode Most ofthe shield tunnels of the R2 line of JinanMetro are located inwater-rich weathered diorite stratum )e groundwater isrich and the weathering degree of the rock stratum isuneven During the EPB shield tunneling many semiopenunder-pressure modes occurred as did the typical problemof a chamber soil sliming Regarding the occurrence of thisproblem and the formulation of proper solutions in thisstudy the parameters of the construction and discharged soilon the construction site and the seepage flow in the chamberare measured A theoretical analysis was conducted and theprinciple and control measures of chamber soil sliming arediscussed herein

2 Project Overview and Problems

21 Project Overview Jinan is the capital of ShandongProvince in China with a total area of 10244 km2 and apermanent population of 75 million as of 2018 Jinan is richin springs which has created challenges for the constructionof the metro lines )e layout of the Jinan Metro lines andthe distribution of the springs are shown in Figure 1 )efirst phase of Jinan Metro line R2 is an east-west urban lineconnecting the key areas of Jinan such as the Lashan areathe core area of the western new city the old urban area andthe high-tech zone It is a backbone rail transit line aiming torelieve the east-west traffic pressure and support the spatialexpansion of the strip city Phase I of the R2 line starts fromWangfuzhuang station in the west and ends at Pen-gjiazhuang station in the east with a total length of ap-proximately 36302 km including a 34502 km undergroundline a 1489 km elevated line and a 0311 km open section)e tunnel is expected to be officially opened to traffic by theend of 2020 )e interval tunnel is being constructed using afour-spoke panel composite-type EPB shield with a cutterhead opening rate of 40 As shown in Figure 2 the cutterhead excavation diameter is 668m and the device isequipped with 37 disc cutters and 48 scrapers )e basicparameters of the shield machine are listed in Table 1 )eburied depth of the tunnel is approximately 49ndash497m andthe geology along the tunnel is complex including com-pletely weathered diorite strongly weathered diorite andmoderately weathered diorite limestone silty clay gravellysoil and sandy-pebble stratum Among these strata thetunnel passes through the weathered diorite for the longest

















China

Yellow River

Yangtze RiverJinan

Jinan

Beijing

N

SYellow River

White spring

Baimai spring

Jade river spring


Hongfanchi spring

0 20 40 Kilometers










10m

20m

30m

A B

C

DE


1003m

K11

+ 70

4

K12

+ 70

7




















4 Results


310 330 340 350300 320Ring number

00

04

08

12

16

20

Pres

sure

(bar

)

pcndashmpwndashm

(a)

310 330 340320 350300Ring number

00

04

08

12

16

20

24

Pres

sure

(bar

)

pcndashbpwndashb

(b)


60

40

20

0

Exca

vatio

n sp

eed

(mm

min

)

300 310 320 330 340 350Ring number

6000

5000

4000

3000

2000

1000

0

Cutti

ng to

rque

(kN

m)










(a) (b)



Wat

er se

epag

e (m

3 )

25 30200500 10 35 40 4515Time (h)

0

5

10

15

20

25

30

35

Measured value






iSA 1

QSA kiSAASAt(1)



hw +(1 minus α2)d

QSB kiSBASBt

(2)




iFA 1

QFA kiFAAFAt(3)



Ground level

Hhw

Hw

Air

Chamber soil

DαD

A

B

L

Groundwaterlevel

(a)

A

B

y

D

xdy

(b)




minus (d2)

hw +(1 minus α)d

hw +(d2) minus y

d2

4minus y

2

1113971

dy

QFB 2kt hw +(1 minus α)d1113858 1113859

minush2

w + hwd1113968



11138681113868111386811138681113868111386811138681113868

1113890 1113891

+ hw +d


α(1 minus α)

1113968+ 157 hw +

d

2minus

h2w + hwd

1113969

1113888 1113889

⎧⎪⎪⎪⎪⎪⎪⎪⎨

⎪⎪⎪⎪⎪⎪⎪⎩

⎫⎪⎪⎪⎪⎪⎪⎪⎬

⎪⎪⎪⎪⎪⎪⎪⎭

(4)











Sk |ΔPP|

ΔXkXk

11138681113868111386811138681113868111386811138681113868

ΔPΔXk

11138681113868111386811138681113868111386811138681113868

11138681113868111386811138681113868111386811138681113868

Xk

P

1113868111386811138681113868111386811138681113868

1113868111386811138681113868111386811138681113868 (5)



60

62

64

66

68

Moi

sture

cont

ent o

f disc

harg

ed so

il (

)

035 040 045 050 055 060 065 070030α

hw = 7mhw = 10m

hw = 13mhw = 16m

Slight sliming

Serious sliming


3530 4005 2510 4500 15 20Time (h)

Wat

er se

epag

e (m

3 )

0

5

10

15

20

25

30

35







20

40

60

80

100

120

Moi

sture

cont

ent o

f disc

harg

ed so

il (

)

hw = 7mhw = 10m

hw = 13mhw = 16m

Serious sliming

Slight sliming

Normal



Serious sliming

Slight sliming

Normal

10

20

30

40

50

60

70

Moi

sture

cont

ent o

f disc

harg

ed so

il (

)


hw = 7mhw = 10m

hw = 13mhw = 16m







5 Discussion






Sensitivity 0056 0113 0769 0692

Serious sliming

Slight sliming

60

62

64

66

68

70M

oistu

re co

nten

t of d

ischa

rged

soil

()


α = 13α = 12α = 23










0

10

20

30

40

50

60Pr

essu

re d

iffer

ence

P (k

Pa)


t = 4hring


Serioussliming

(a)

0

10

20

30

40

50

60

Pres

sure

diff

eren

ce P

(kPa

)


t = 6hring


Serioussliming

(b)

0

10

20

30

40

50

60

Pres

sure

diff

eren

ce P

(kPa

)


t = 8hring

NormalSlight


(c)








6 Conclusions






Data Availability




Acknowledgments


References

















































China

Yellow River

Yangtze RiverJinan

Jinan

Beijing

N

SYellow River

White spring

Baimai spring

Jade river spring


Hongfanchi spring

0 20 40 Kilometers










10m

20m

30m

A B

C

DE


1003m

K11

+ 70

4

K12

+ 70

7




















4 Results


310 330 340 350300 320Ring number

00

04

08

12

16

20

Pres

sure

(bar

)

pcndashmpwndashm

(a)

310 330 340320 350300Ring number

00

04

08

12

16

20

24

Pres

sure

(bar

)

pcndashbpwndashb

(b)


60

40

20

0

Exca

vatio

n sp

eed

(mm

min

)

300 310 320 330 340 350Ring number

6000

5000

4000

3000

2000

1000

0

Cutti

ng to

rque

(kN

m)










(a) (b)



Wat

er se

epag

e (m

3 )

25 30200500 10 35 40 4515Time (h)

0

5

10

15

20

25

30

35

Measured value






iSA 1

QSA kiSAASAt(1)



hw +(1 minus α2)d

QSB kiSBASBt

(2)




iFA 1

QFA kiFAAFAt(3)



Ground level

Hhw

Hw

Air

Chamber soil

DαD

A

B

L

Groundwaterlevel

(a)

A

B

y

D

xdy

(b)




minus (d2)

hw +(1 minus α)d

hw +(d2) minus y

d2

4minus y

2

1113971

dy

QFB 2kt hw +(1 minus α)d1113858 1113859

minush2

w + hwd1113968



11138681113868111386811138681113868111386811138681113868

1113890 1113891

+ hw +d


α(1 minus α)

1113968+ 157 hw +

d

2minus

h2w + hwd

1113969

1113888 1113889

⎧⎪⎪⎪⎪⎪⎪⎪⎨

⎪⎪⎪⎪⎪⎪⎪⎩

⎫⎪⎪⎪⎪⎪⎪⎪⎬

⎪⎪⎪⎪⎪⎪⎪⎭

(4)











Sk |ΔPP|

ΔXkXk

11138681113868111386811138681113868111386811138681113868

ΔPΔXk

11138681113868111386811138681113868111386811138681113868

11138681113868111386811138681113868111386811138681113868

Xk

P

1113868111386811138681113868111386811138681113868

1113868111386811138681113868111386811138681113868 (5)



60

62

64

66

68

Moi

sture

cont

ent o

f disc

harg

ed so

il (

)

035 040 045 050 055 060 065 070030α

hw = 7mhw = 10m

hw = 13mhw = 16m

Slight sliming

Serious sliming


3530 4005 2510 4500 15 20Time (h)

Wat

er se

epag

e (m

3 )

0

5

10

15

20

25

30

35







20

40

60

80

100

120

Moi

sture

cont

ent o

f disc

harg

ed so

il (

)

hw = 7mhw = 10m

hw = 13mhw = 16m

Serious sliming

Slight sliming

Normal



Serious sliming

Slight sliming

Normal

10

20

30

40

50

60

70

Moi

sture

cont

ent o

f disc

harg

ed so

il (

)


hw = 7mhw = 10m

hw = 13mhw = 16m







5 Discussion






Sensitivity 0056 0113 0769 0692

Serious sliming

Slight sliming

60

62

64

66

68

70M

oistu

re co

nten

t of d

ischa

rged

soil

()


α = 13α = 12α = 23










0

10

20

30

40

50

60Pr

essu

re d

iffer

ence

P (k

Pa)


t = 4hring


Serioussliming

(a)

0

10

20

30

40

50

60

Pres

sure

diff

eren

ce P

(kPa

)


t = 6hring


Serioussliming

(b)

0

10

20

30

40

50

60

Pres

sure

diff

eren

ce P

(kPa

)


t = 8hring

NormalSlight


(c)








6 Conclusions






Data Availability




Acknowledgments


References








































10m

20m

30m

A B

C

DE


1003m

K11

+ 70

4

K12

+ 70

7




















4 Results


310 330 340 350300 320Ring number

00

04

08

12

16

20

Pres

sure

(bar

)

pcndashmpwndashm

(a)

310 330 340320 350300Ring number

00

04

08

12

16

20

24

Pres

sure

(bar

)

pcndashbpwndashb

(b)


60

40

20

0

Exca

vatio

n sp

eed

(mm

min

)

300 310 320 330 340 350Ring number

6000

5000

4000

3000

2000

1000

0

Cutti

ng to

rque

(kN

m)










(a) (b)



Wat

er se

epag

e (m

3 )

25 30200500 10 35 40 4515Time (h)

0

5

10

15

20

25

30

35

Measured value






iSA 1

QSA kiSAASAt(1)



hw +(1 minus α2)d

QSB kiSBASBt

(2)




iFA 1

QFA kiFAAFAt(3)



Ground level

Hhw

Hw

Air

Chamber soil

DαD

A

B

L

Groundwaterlevel

(a)

A

B

y

D

xdy

(b)




minus (d2)

hw +(1 minus α)d

hw +(d2) minus y

d2

4minus y

2

1113971

dy

QFB 2kt hw +(1 minus α)d1113858 1113859

minush2

w + hwd1113968



11138681113868111386811138681113868111386811138681113868

1113890 1113891

+ hw +d


α(1 minus α)

1113968+ 157 hw +

d

2minus

h2w + hwd

1113969

1113888 1113889

⎧⎪⎪⎪⎪⎪⎪⎪⎨

⎪⎪⎪⎪⎪⎪⎪⎩

⎫⎪⎪⎪⎪⎪⎪⎪⎬

⎪⎪⎪⎪⎪⎪⎪⎭

(4)











Sk |ΔPP|

ΔXkXk

11138681113868111386811138681113868111386811138681113868

ΔPΔXk

11138681113868111386811138681113868111386811138681113868

11138681113868111386811138681113868111386811138681113868

Xk

P

1113868111386811138681113868111386811138681113868

1113868111386811138681113868111386811138681113868 (5)



60

62

64

66

68

Moi

sture

cont

ent o

f disc

harg

ed so

il (

)

035 040 045 050 055 060 065 070030α

hw = 7mhw = 10m

hw = 13mhw = 16m

Slight sliming

Serious sliming


3530 4005 2510 4500 15 20Time (h)

Wat

er se

epag

e (m

3 )

0

5

10

15

20

25

30

35







20

40

60

80

100

120

Moi

sture

cont

ent o

f disc

harg

ed so

il (

)

hw = 7mhw = 10m

hw = 13mhw = 16m

Serious sliming

Slight sliming

Normal



Serious sliming

Slight sliming

Normal

10

20

30

40

50

60

70

Moi

sture

cont

ent o

f disc

harg

ed so

il (

)


hw = 7mhw = 10m

hw = 13mhw = 16m







5 Discussion






Sensitivity 0056 0113 0769 0692

Serious sliming

Slight sliming

60

62

64

66

68

70M

oistu

re co

nten

t of d

ischa

rged

soil

()


α = 13α = 12α = 23










0

10

20

30

40

50

60Pr

essu

re d

iffer

ence

P (k

Pa)


t = 4hring


Serioussliming

(a)

0

10

20

30

40

50

60

Pres

sure

diff

eren

ce P

(kPa

)


t = 6hring


Serioussliming

(b)

0

10

20

30

40

50

60

Pres

sure

diff

eren

ce P

(kPa

)


t = 8hring

NormalSlight


(c)








6 Conclusions






Data Availability




Acknowledgments


References













































4 Results


310 330 340 350300 320Ring number

00

04

08

12

16

20

Pres

sure

(bar

)

pcndashmpwndashm

(a)

310 330 340320 350300Ring number

00

04

08

12

16

20

24

Pres

sure

(bar

)

pcndashbpwndashb

(b)


60

40

20

0

Exca

vatio

n sp

eed

(mm

min

)

300 310 320 330 340 350Ring number

6000

5000

4000

3000

2000

1000

0

Cutti

ng to

rque

(kN

m)










(a) (b)



Wat

er se

epag

e (m

3 )

25 30200500 10 35 40 4515Time (h)

0

5

10

15

20

25

30

35

Measured value






iSA 1

QSA kiSAASAt(1)



hw +(1 minus α2)d

QSB kiSBASBt

(2)




iFA 1

QFA kiFAAFAt(3)



Ground level

Hhw

Hw

Air

Chamber soil

DαD

A

B

L

Groundwaterlevel

(a)

A

B

y

D

xdy

(b)




minus (d2)

hw +(1 minus α)d

hw +(d2) minus y

d2

4minus y

2

1113971

dy

QFB 2kt hw +(1 minus α)d1113858 1113859

minush2

w + hwd1113968



11138681113868111386811138681113868111386811138681113868

1113890 1113891

+ hw +d


α(1 minus α)

1113968+ 157 hw +

d

2minus

h2w + hwd

1113969

1113888 1113889

⎧⎪⎪⎪⎪⎪⎪⎪⎨

⎪⎪⎪⎪⎪⎪⎪⎩

⎫⎪⎪⎪⎪⎪⎪⎪⎬

⎪⎪⎪⎪⎪⎪⎪⎭

(4)











Sk |ΔPP|

ΔXkXk

11138681113868111386811138681113868111386811138681113868

ΔPΔXk

11138681113868111386811138681113868111386811138681113868

11138681113868111386811138681113868111386811138681113868

Xk

P

1113868111386811138681113868111386811138681113868

1113868111386811138681113868111386811138681113868 (5)



60

62

64

66

68

Moi

sture

cont

ent o

f disc

harg

ed so

il (

)

035 040 045 050 055 060 065 070030α

hw = 7mhw = 10m

hw = 13mhw = 16m

Slight sliming

Serious sliming


3530 4005 2510 4500 15 20Time (h)

Wat

er se

epag

e (m

3 )

0

5

10

15

20

25

30

35







20

40

60

80

100

120

Moi

sture

cont

ent o

f disc

harg

ed so

il (

)

hw = 7mhw = 10m

hw = 13mhw = 16m

Serious sliming

Slight sliming

Normal



Serious sliming

Slight sliming

Normal

10

20

30

40

50

60

70

Moi

sture

cont

ent o

f disc

harg

ed so

il (

)


hw = 7mhw = 10m

hw = 13mhw = 16m







5 Discussion






Sensitivity 0056 0113 0769 0692

Serious sliming

Slight sliming

60

62

64

66

68

70M

oistu

re co

nten

t of d

ischa

rged

soil

()


α = 13α = 12α = 23










0

10

20

30

40

50

60Pr

essu

re d

iffer

ence

P (k

Pa)


t = 4hring


Serioussliming

(a)

0

10

20

30

40

50

60

Pres

sure

diff

eren

ce P

(kPa

)


t = 6hring


Serioussliming

(b)

0

10

20

30

40

50

60

Pres

sure

diff

eren

ce P

(kPa

)


t = 8hring

NormalSlight


(c)








6 Conclusions






Data Availability




Acknowledgments


References




































4 Results


310 330 340 350300 320Ring number

00

04

08

12

16

20

Pres

sure

(bar

)

pcndashmpwndashm

(a)

310 330 340320 350300Ring number

00

04

08

12

16

20

24

Pres

sure

(bar

)

pcndashbpwndashb

(b)


60

40

20

0

Exca

vatio

n sp

eed

(mm

min

)

300 310 320 330 340 350Ring number

6000

5000

4000

3000

2000

1000

0

Cutti

ng to

rque

(kN

m)










(a) (b)



Wat

er se

epag

e (m

3 )

25 30200500 10 35 40 4515Time (h)

0

5

10

15

20

25

30

35

Measured value






iSA 1

QSA kiSAASAt(1)



hw +(1 minus α2)d

QSB kiSBASBt

(2)




iFA 1

QFA kiFAAFAt(3)



Ground level

Hhw

Hw

Air

Chamber soil

DαD

A

B

L

Groundwaterlevel

(a)

A

B

y

D

xdy

(b)




minus (d2)

hw +(1 minus α)d

hw +(d2) minus y

d2

4minus y

2

1113971

dy

QFB 2kt hw +(1 minus α)d1113858 1113859

minush2

w + hwd1113968



11138681113868111386811138681113868111386811138681113868

1113890 1113891

+ hw +d


α(1 minus α)

1113968+ 157 hw +

d

2minus

h2w + hwd

1113969

1113888 1113889

⎧⎪⎪⎪⎪⎪⎪⎪⎨

⎪⎪⎪⎪⎪⎪⎪⎩

⎫⎪⎪⎪⎪⎪⎪⎪⎬

⎪⎪⎪⎪⎪⎪⎪⎭

(4)











Sk |ΔPP|

ΔXkXk

11138681113868111386811138681113868111386811138681113868

ΔPΔXk

11138681113868111386811138681113868111386811138681113868

11138681113868111386811138681113868111386811138681113868

Xk

P

1113868111386811138681113868111386811138681113868

1113868111386811138681113868111386811138681113868 (5)



60

62

64

66

68

Moi

sture

cont

ent o

f disc

harg

ed so

il (

)

035 040 045 050 055 060 065 070030α

hw = 7mhw = 10m

hw = 13mhw = 16m

Slight sliming

Serious sliming


3530 4005 2510 4500 15 20Time (h)

Wat

er se

epag

e (m

3 )

0

5

10

15

20

25

30

35







20

40

60

80

100

120

Moi

sture

cont

ent o

f disc

harg

ed so

il (

)

hw = 7mhw = 10m

hw = 13mhw = 16m

Serious sliming

Slight sliming

Normal



Serious sliming

Slight sliming

Normal

10

20

30

40

50

60

70

Moi

sture

cont

ent o

f disc

harg

ed so

il (

)


hw = 7mhw = 10m

hw = 13mhw = 16m







5 Discussion






Sensitivity 0056 0113 0769 0692

Serious sliming

Slight sliming

60

62

64

66

68

70M

oistu

re co

nten

t of d

ischa

rged

soil

()


α = 13α = 12α = 23










0

10

20

30

40

50

60Pr

essu

re d

iffer

ence

P (k

Pa)


t = 4hring


Serioussliming

(a)

0

10

20

30

40

50

60

Pres

sure

diff

eren

ce P

(kPa

)


t = 6hring


Serioussliming

(b)

0

10

20

30

40

50

60

Pres

sure

diff

eren

ce P

(kPa

)


t = 8hring

NormalSlight


(c)








6 Conclusions






Data Availability




Acknowledgments


References






































(a) (b)



Wat

er se

epag

e (m

3 )

25 30200500 10 35 40 4515Time (h)

0

5

10

15

20

25

30

35

Measured value






iSA 1

QSA kiSAASAt(1)



hw +(1 minus α2)d

QSB kiSBASBt

(2)




iFA 1

QFA kiFAAFAt(3)



Ground level

Hhw

Hw

Air

Chamber soil

DαD

A

B

L

Groundwaterlevel

(a)

A

B

y

D

xdy

(b)




minus (d2)

hw +(1 minus α)d

hw +(d2) minus y

d2

4minus y

2

1113971

dy

QFB 2kt hw +(1 minus α)d1113858 1113859

minush2

w + hwd1113968



11138681113868111386811138681113868111386811138681113868

1113890 1113891

+ hw +d


α(1 minus α)

1113968+ 157 hw +

d

2minus

h2w + hwd

1113969

1113888 1113889

⎧⎪⎪⎪⎪⎪⎪⎪⎨

⎪⎪⎪⎪⎪⎪⎪⎩

⎫⎪⎪⎪⎪⎪⎪⎪⎬

⎪⎪⎪⎪⎪⎪⎪⎭

(4)











Sk |ΔPP|

ΔXkXk

11138681113868111386811138681113868111386811138681113868

ΔPΔXk

11138681113868111386811138681113868111386811138681113868

11138681113868111386811138681113868111386811138681113868

Xk

P

1113868111386811138681113868111386811138681113868

1113868111386811138681113868111386811138681113868 (5)



60

62

64

66

68

Moi

sture

cont

ent o

f disc

harg

ed so

il (

)

035 040 045 050 055 060 065 070030α

hw = 7mhw = 10m

hw = 13mhw = 16m

Slight sliming

Serious sliming


3530 4005 2510 4500 15 20Time (h)

Wat

er se

epag

e (m

3 )

0

5

10

15

20

25

30

35







20

40

60

80

100

120

Moi

sture

cont

ent o

f disc

harg

ed so

il (

)

hw = 7mhw = 10m

hw = 13mhw = 16m

Serious sliming

Slight sliming

Normal



Serious sliming

Slight sliming

Normal

10

20

30

40

50

60

70

Moi

sture

cont

ent o

f disc

harg

ed so

il (

)


hw = 7mhw = 10m

hw = 13mhw = 16m







5 Discussion






Sensitivity 0056 0113 0769 0692

Serious sliming

Slight sliming

60

62

64

66

68

70M

oistu

re co

nten

t of d

ischa

rged

soil

()


α = 13α = 12α = 23










0

10

20

30

40

50

60Pr

essu

re d

iffer

ence

P (k

Pa)


t = 4hring


Serioussliming

(a)

0

10

20

30

40

50

60

Pres

sure

diff

eren

ce P

(kPa

)


t = 6hring


Serioussliming

(b)

0

10

20

30

40

50

60

Pres

sure

diff

eren

ce P

(kPa

)


t = 8hring

NormalSlight


(c)








6 Conclusions






Data Availability




Acknowledgments


References





































iSA 1

QSA kiSAASAt(1)



hw +(1 minus α2)d

QSB kiSBASBt

(2)




iFA 1

QFA kiFAAFAt(3)



Ground level

Hhw

Hw

Air

Chamber soil

DαD

A

B

L

Groundwaterlevel

(a)

A

B

y

D

xdy

(b)




minus (d2)

hw +(1 minus α)d

hw +(d2) minus y

d2

4minus y

2

1113971

dy

QFB 2kt hw +(1 minus α)d1113858 1113859

minush2

w + hwd1113968



11138681113868111386811138681113868111386811138681113868

1113890 1113891

+ hw +d


α(1 minus α)

1113968+ 157 hw +

d

2minus

h2w + hwd

1113969

1113888 1113889

⎧⎪⎪⎪⎪⎪⎪⎪⎨

⎪⎪⎪⎪⎪⎪⎪⎩

⎫⎪⎪⎪⎪⎪⎪⎪⎬

⎪⎪⎪⎪⎪⎪⎪⎭

(4)











Sk |ΔPP|

ΔXkXk

11138681113868111386811138681113868111386811138681113868

ΔPΔXk

11138681113868111386811138681113868111386811138681113868

11138681113868111386811138681113868111386811138681113868

Xk

P

1113868111386811138681113868111386811138681113868

1113868111386811138681113868111386811138681113868 (5)



60

62

64

66

68

Moi

sture

cont

ent o

f disc

harg

ed so

il (

)

035 040 045 050 055 060 065 070030α

hw = 7mhw = 10m

hw = 13mhw = 16m

Slight sliming

Serious sliming


3530 4005 2510 4500 15 20Time (h)

Wat

er se

epag

e (m

3 )

0

5

10

15

20

25

30

35







20

40

60

80

100

120

Moi

sture

cont

ent o

f disc

harg

ed so

il (

)

hw = 7mhw = 10m

hw = 13mhw = 16m

Serious sliming

Slight sliming

Normal



Serious sliming

Slight sliming

Normal

10

20

30

40

50

60

70

Moi

sture

cont

ent o

f disc

harg

ed so

il (

)


hw = 7mhw = 10m

hw = 13mhw = 16m







5 Discussion






Sensitivity 0056 0113 0769 0692

Serious sliming

Slight sliming

60

62

64

66

68

70M

oistu

re co

nten

t of d

ischa

rged

soil

()


α = 13α = 12α = 23










0

10

20

30

40

50

60Pr

essu

re d

iffer

ence

P (k

Pa)


t = 4hring


Serioussliming

(a)

0

10

20

30

40

50

60

Pres

sure

diff

eren

ce P

(kPa

)


t = 6hring


Serioussliming

(b)

0

10

20

30

40

50

60

Pres

sure

diff

eren

ce P

(kPa

)


t = 8hring

NormalSlight


(c)








6 Conclusions






Data Availability




Acknowledgments


References



































minus (d2)

hw +(1 minus α)d

hw +(d2) minus y

d2

4minus y

2

1113971

dy

QFB 2kt hw +(1 minus α)d1113858 1113859

minush2

w + hwd1113968



11138681113868111386811138681113868111386811138681113868

1113890 1113891

+ hw +d


α(1 minus α)

1113968+ 157 hw +

d

2minus

h2w + hwd

1113969

1113888 1113889

⎧⎪⎪⎪⎪⎪⎪⎪⎨

⎪⎪⎪⎪⎪⎪⎪⎩

⎫⎪⎪⎪⎪⎪⎪⎪⎬

⎪⎪⎪⎪⎪⎪⎪⎭

(4)











Sk |ΔPP|

ΔXkXk

11138681113868111386811138681113868111386811138681113868

ΔPΔXk

11138681113868111386811138681113868111386811138681113868

11138681113868111386811138681113868111386811138681113868

Xk

P

1113868111386811138681113868111386811138681113868

1113868111386811138681113868111386811138681113868 (5)



60

62

64

66

68

Moi

sture

cont

ent o

f disc

harg

ed so

il (

)

035 040 045 050 055 060 065 070030α

hw = 7mhw = 10m

hw = 13mhw = 16m

Slight sliming

Serious sliming


3530 4005 2510 4500 15 20Time (h)

Wat

er se

epag

e (m

3 )

0

5

10

15

20

25

30

35







20

40

60

80

100

120

Moi

sture

cont

ent o

f disc

harg

ed so

il (

)

hw = 7mhw = 10m

hw = 13mhw = 16m

Serious sliming

Slight sliming

Normal



Serious sliming

Slight sliming

Normal

10

20

30

40

50

60

70

Moi

sture

cont

ent o

f disc

harg

ed so

il (

)


hw = 7mhw = 10m

hw = 13mhw = 16m







5 Discussion






Sensitivity 0056 0113 0769 0692

Serious sliming

Slight sliming

60

62

64

66

68

70M

oistu

re co

nten

t of d

ischa

rged

soil

()


α = 13α = 12α = 23










0

10

20

30

40

50

60Pr

essu

re d

iffer

ence

P (k

Pa)


t = 4hring


Serioussliming

(a)

0

10

20

30

40

50

60

Pres

sure

diff

eren

ce P

(kPa

)


t = 6hring


Serioussliming

(b)

0

10

20

30

40

50

60

Pres

sure

diff

eren

ce P

(kPa

)


t = 8hring

NormalSlight


(c)








6 Conclusions






Data Availability




Acknowledgments


References




































Sk |ΔPP|

ΔXkXk

11138681113868111386811138681113868111386811138681113868

ΔPΔXk

11138681113868111386811138681113868111386811138681113868

11138681113868111386811138681113868111386811138681113868

Xk

P

1113868111386811138681113868111386811138681113868

1113868111386811138681113868111386811138681113868 (5)



60

62

64

66

68

Moi

sture

cont

ent o

f disc

harg

ed so

il (

)

035 040 045 050 055 060 065 070030α

hw = 7mhw = 10m

hw = 13mhw = 16m

Slight sliming

Serious sliming


3530 4005 2510 4500 15 20Time (h)

Wat

er se

epag

e (m

3 )

0

5

10

15

20

25

30

35







20

40

60

80

100

120

Moi

sture

cont

ent o

f disc

harg

ed so

il (

)

hw = 7mhw = 10m

hw = 13mhw = 16m

Serious sliming

Slight sliming

Normal



Serious sliming

Slight sliming

Normal

10

20

30

40

50

60

70

Moi

sture

cont

ent o

f disc

harg

ed so

il (

)


hw = 7mhw = 10m

hw = 13mhw = 16m







5 Discussion






Sensitivity 0056 0113 0769 0692

Serious sliming

Slight sliming

60

62

64

66

68

70M

oistu

re co

nten

t of d

ischa

rged

soil

()


α = 13α = 12α = 23










0

10

20

30

40

50

60Pr

essu

re d

iffer

ence

P (k

Pa)


t = 4hring


Serioussliming

(a)

0

10

20

30

40

50

60

Pres

sure

diff

eren

ce P

(kPa

)


t = 6hring


Serioussliming

(b)

0

10

20

30

40

50

60

Pres

sure

diff

eren

ce P

(kPa

)


t = 8hring

NormalSlight


(c)








6 Conclusions






Data Availability




Acknowledgments


References






































5 Discussion






Sensitivity 0056 0113 0769 0692

Serious sliming

Slight sliming

60

62

64

66

68

70M

oistu

re co

nten

t of d

ischa

rged

soil

()


α = 13α = 12α = 23










0

10

20

30

40

50

60Pr

essu

re d

iffer

ence

P (k

Pa)


t = 4hring


Serioussliming

(a)

0

10

20

30

40

50

60

Pres

sure

diff

eren

ce P

(kPa

)


t = 6hring


Serioussliming

(b)

0

10

20

30

40

50

60

Pres

sure

diff

eren

ce P

(kPa

)


t = 8hring

NormalSlight


(c)








6 Conclusions






Data Availability




Acknowledgments


References





































0

10

20

30

40

50

60Pr

essu

re d

iffer

ence

P (k

Pa)


t = 4hring


Serioussliming

(a)

0

10

20

30

40

50

60

Pres

sure

diff

eren

ce P

(kPa

)


t = 6hring


Serioussliming

(b)

0

10

20

30

40

50

60

Pres

sure

diff

eren

ce P

(kPa

)


t = 8hring

NormalSlight


(c)








6 Conclusions






Data Availability




Acknowledgments


References







































6 Conclusions






Data Availability




Acknowledgments


References


































Data Availability




Acknowledgments


References





































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