Luận án tiến sĩ: Physical and numerical modelling of the soft soil ground improved by deep cement mixing method

PHYSICAL AND NUMERICAL MODELLING OF THE SOFT SOIL GROUND IMPROVED BY DEEP CEMENT MIXING METHOD ZHEN FANG Ph.D.. GROUND IMPROVED BY DEEP CEMENT MIXING METHODsubmitted by Zhen Fangfor the

SOFT SOIL GROUND IMPROVED BY DEEP

CEMENT MIXING METHOD

By

Zhen FANGBEng, MSc

Supervisor: Professor Jian-Hua YIN

A Thesis Submitted in Partial Fulfilment of the Requirements

for the Degree of Doctor of Philosophy

&

Department of Civil and Structural EngineeringThe Hong Kong Polytechnic University

May 2006

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PHYSICAL AND NUMERICAL MODELLING OF THE

SOFT SOIL GROUND IMPROVED BY DEEP

CEMENT MIXING METHOD

ZHEN FANG

Ph.D

THE HONG KONG POLYTECHNIC UNIVERSITY

2006

Soft Soil Ground Improved by Deep Cement Mixing Method” is my own work andthat, to the best of my knowledge and belief, it reproduces no material previouslypublished or written nor material which has been accepted for the award of any other

degree or diploma, except where due acknowledgement has been made in the text

Signed: Zhe Pt

Name: Zhen FANG

GROUND IMPROVED BY DEEP CEMENT MIXING METHOD

submitted by Zhen Fangfor the degree of Doctor of Philosophy

at The Hong Kong Polytechnic University in May 2006

The research described in this thesis focuses on the consolidation behaviour andvertical bearing capacity of soft soil ground improved by Deep Cement Mixing (DCM)method The soft soil ground modelled in this study may support relatively lightstructures, reclaimed fills or road embankments

Firstly, an axisymmetric physical model (Model 1) test was carried out to investigatethe consolidation behaviour of soft soil ground installed with a single DCM column.The surface settlement, excess pore water pressures at different locations in the soil,and pressures carried by the soil and the DCM column were all measured throughouttesting This model test revealed that the DCM column behaved as a vertical drainpartially, which suggests that the DCM column might be regarded as a partial or fullvertical drainage, somewhat similar to a Prefabricated Vertical Drain (PVD) or a sanddrain in the DCM improved ground Under the approximate rigid loading, thepressure on the surrounding soil was progressively transferred to the DCM column,which caused an increase in stress concentration ratio The stress concentration ratiowas also found to be dependent on both the external pressure and the degree ofconsolidation of the surrounding soil

test on the soft soil installed with a PVD strip was performed This model test wasattempted to make a comparative study on the dissipation of excess pore waterpressure mechanism between the soil ground installed with DCM column and the soil

ground installed with PVD strip Compared to Model 1 test, the excess pore waterpressure in the soil of Model 2 test was observed to dissipate slowly under the sameload increment This difference was mainly due to the different changing patterns ofthe surcharge carried by soft soil in the two model tests The surcharge carried by soilwas nearly constant for the soil with PVD strip in Model 2 test, but reducing graduallyfor the soil ground with DCM column in Model 1 test

After Model 1 test and Model 2 test, Model 3 test was carried out Model 3 was aplane strain model consisting of a soft soil ground installed with nine mini DCMcolumns The DCM columns were covered by a thin sand layer and rigid plate, which

was then subjected to a vertical load Model 3 test was used to investigate the vertical

bearing capacity, and the failure mode of the soil ground improved by a DCM column

group Establishment of the model ground and the arrangement of transducers areboth presented in detail Throughout the test, surface settlement, pore pressures and

the stress carried by soil were all measured The recorded load versus displacement

curve represents pronounced softening, which implies the progressive failure of the

column group in the model ground It was observed that responses of pore pressurewere dependent on not only the drainage condition but also the local failure of DCMcolumns and the progressive failure of the column group However, effective stresspaths of soil elements in the ground could be useful tool to interpret the pore pressureresponses reasonably Moreover, post-test study verifies a wedge-shaped failure mode

Numerical modelling was carried out in an attempt to improve understanding of the

consolidation process and the failure mechanism of the improved soil ground In order

to take account of the time-dependent behaviour of soft soil, an Elastic Visco-Plastic(EVP) model is needed For this purpose, a three-dimensional (3-D) EVP constitutive

model originally proposed by Yin and Graham (1999) has been incorporated into a

Finite Element (FE) package, ABAQUS, by means of a User MATerial (UMAT)FORTRAN subroutine This model is formulated as incremental stress-strainrelationship for use in FE analysis For the purpose of verification, a number of singleelement numerical experiments were carried out to evaluate the overall performanceand the efficiency of the UMAT subroutine

Finite element package associated with UMAT developed in this study was employed

to conduct FE analysis on two model tests (Model 1 and Model 3) The softening

behaviour of the DCM column has been incorporated by employing Mohr-Coulombconstitutive model with the progressive reduction of the cohesion with the deviatoricplastic strain In terms of Model 1 test, fairly good agreement between measurementsand computations is obtained In particular, the sudden changes of the excess pore

pressure resulted from the DCM column failure has been well captured Based on a

series of parametric studies, the permeability of the DCM column and the viscosity ofthe surrounding soil were found to have an influence on the dissipation of excess porepressure in the soil, but little influence on the stress concentration ratio Finite elementanalysis was also performed on Model 3 test The results reveal that there is good

vertical bearing capacity of the DCM treated soil ground has been well predicted.Besides, the degradation process of the vertical bearing capacity has been reproducedsuccessfully with the introduction of the softening behaviour of the DCM columns.

Two field cases involving DCM method have been simulated using FE models withthe UMAT The permeability of DCM columns has been set to be much higher thanthat of surrounding soil Computed results are in good agreement with fieldmeasurements It is demonstrated that the permeability of the DCM column has anegligible influence on the deformation of the improved soil ground This alsoindicates that a successful prediction of the performance of soil ground with DCMcolumns shall take account of the permeability of the DCM column In order toidentify the influence of soil viscosity on the current problems, one more elasticplastic (EP) FE analysis has been made, in which the Modified Cam-Clay (MCC)model is used to model the soft soil A comparison between them reveals that EVPmodelling is capable of providing better results than EP modelling, particularly for thelong-term deformation

At the end of this thesis, a summary of the major conclusions and somerecommendations for further studies are presented

1 Fang, Z and Yin, J.H (2006) A model study on soft soil ground installed withcement-soil columns subjected to vertical loading Submitted to Geotechnique.

2 Fang, Z and Yin, J.H (2006) Experimental study on consolidation process ofmarine clay around a soil-cement column International Journal of Geomechanics

marine clay Geotechnique, 56(1), 63-68

5 Zhou, C., Yin, J.H and Fang, Z (2005) Experimental and numerical analysis ofthe progressive deformation and failure of marine clay improved with deepcement mixing column Rock and Soil Mechanics, 26, 205-208 (In Chinese)

Conference Papers

1 Fang, Z and Yin, J.H (2004) Physical modelling study on the compositefoundation of a cement-soil-mixed column in soft Hong Kong marine clay.Annual Conference of Hong Kong Society of Theoretical and Applied Mechanics

2003-2004, Hong Kong

2 Fang, Z and Yin, J.H (2005) Physical modelling study on the consolidation

behavior of a composite foundation improved by DCM Proceedings of the 11"

Advances in Geomechanics, Italy, June 2005 Vol.1, 667-674.

Fang, Z., Yin, J.H., Zhou, C and Zhu, J.G (2006) Elastic Viscoplastic modelling

of two cases involving PVD improved Hong Kong marine clay 4” International

Conference on Soil Engineering '2006, Vancouver, Canada, October 2006(Accepted)

Yin, J.H and Fang, Z (2006) Physical modelling of the consolidation behavior

of soft soil ground installed with vertical drains or deep cement mixed soilcolumns International Conference on Physical Modelling in Geotechnics, Hong

Kong, August 2006

guidance and patience has been invaluable, and is greatly appreciated Without hisencouragement, understanding and continuous support, it would not have beenpossible to complete my work.

I would also like to thank members of my oral examination committee, ProfessorsC.W Li, D.T Bergado and X.S Li for reviewing the manuscript and offeringvaluable comments and suggestions

Many thanks are due to Mr Y.P Leung and K.R Lam for their great help when Icarried out tests in the Soil Mechanics Laboratory of Department of Civil andStructural Engineering of The Hong Kong Polytechnic University Other peoplewhom I would particularly like to thank are: Professor G.F Zhu, Dr S.K Shukla,Professor J.G Zhu and Dr C Zhou for their help with proof reading of the thesis,FORTRAN programming and numerical simulations Discussions with Mr S.Y.Wang of City University of Hong Kong are also appreciated Thanks are alsoextended to Professor X.J Yu and Mrs Y Yan of the Geotechnical Research Institute

of Hohai University who introduced me to the world of the Soil Mechanics

Financial supports from the RGC grant (No: PolyU 5055/02E) of The Hong KongGovernment are deeply appreciated Also, administrative and technical supports fromthe staff of the Department of Civil and Structural Engineering are appreciated

I am in the debt of my family and my girl friend who suffered from my long absence

2.2.4.3 Stiffness ceeecceesceceeecesceeerecessscessecesaeeeseevssevessorerscreseccssesceresennes 17

2.2.4.4 Compressibility -‹ - 5-55 nhe 18

2.2.4.5 Drained and undrained strength -c-ccccccsneeeesre 19

2.2.4.6 Viscosity and creep -c-cccnennnhnhhhnnhhehhHhHH re 20

2.2.4.7 Permeability -5-°scs hen 20

2.3 Bearing capacity of the DM ground -‹ -‹-‹ ‹ -5-5cccccssnshhehehtrrreriree 21

2.3.1 Single column ‹ -‹ - - 5-55 nh are 21

2.3.2 Group Columns -‹ 55-5 55°5*S+tnthhHHHHHHHHờ 23

2.4 Consolidation theory of the DM ground -++ccrteeseierrrrerere 25

2.5 Failure patterns involved in the DM ground -‹ -: -5-s+cresseersee 31

2.5.1 Single column + + 52222 HH He 31

2.5.2 Soil ground with group columns -: -‹ : -‹e++s<++++estereerrrerererre 31

2.6 Geotechnical characteristics of Hong Kong marine clay -:: - 31

2.6.1 Physical and chemical properties + +: ses eseseeeeeeeeneneseey 31

2.6.2 Compressibility characteristics ‹ ‹ ‹ -cc<<ceshhhhhhherie 32

2.6.3 Undrained shear strength and critical state parameters -: : -: 32

2.6.4 Permeability -‹ -‹ - sen HH Hà tre 33

2.6.5 Viscosity and creep -‹ -:5c-c nọ HH HH in 33

CHAPTER3 MODEL 1 TEST: AXISYMMTRIC CASE - 75

3.1 Introduction - - << << Ă <1 1 nọ nọ To T0 0100970 75

3.2.2 Selection of testing materials -scnnnnhehhehhtrrrrre 16

3.2.3 Preparation of DCM column -ccccsccseeereirerrrrrrrrre 16

3.2.4 Data acquisition system -‹ -‹ - con 77

3.3 Calibration of transducers - <6 S5 11191 nh, 77

kh nhớ n8 17

c0 78

khe 78

kh 9n 78

3.4 Model preparation procedures -: : : :-++crstnnenhhrehhhererrrrde 78

3.4.1 Setting up the bottom geotextile -:-+esccsnnhhnehhererrrrre 79

3.4.2 Installation Of PPTs ‹ - c5 S1 233g ng ng kg 70

3.4.3 Pouring clay slurry -c+ccstenenethhhhhethhehhehhhhie 7Q

3.4.4 Consolidation of the Clay -:: c-ccceseethhhhhhhhhhhrè 719

3.4.5 Installation of the DCM column ‹‹-‹‹ -: - < <5- <5 SĂĂ 1s se 80

3.4.6 Paving the top sand layer ‹-‹ ‹ :5- 5⁄22 thi 81

3.4.7 Assembly of the loading system -‹ -c-c-+ceceeseeeeie 81

3.4.8 Installation Of LVDT ‹ -‹: -‹ -cc- << <5 <1 0110119 ng như 81

3.5 Test procedures ‹-‹ -: 5-5 Sàn HH 0 0H tt 82

3.6 Test results and discussions ‹ -: <5 Ă Ă 11 HH nh 82

3.6.1 Consolidation settlement ‹ - - - - - - - <5 52114 1 1 1 n6 83

3.6.2 EXcess pore pressure responses +++ 252 2n 83

3.6.3 Vertical and radial drainage ‹ -5+ss nh 84

3.6.3.1 Vertical drainage ‹ -‹ ©s+thnhhhnhHHHHHHHHH 0 t0 tờ 84

3.7 Post-test investigations Á 88

3.7.1 nh con 88

3.7.2 Routine tests on the clay Ớ%mTmẲi 89

3.5 Scale effect -eccccecececscsecscccesesrsecsressseseeseeeeseeeeenseeeeenens esses ee eeee see eeens noses ns eenseser 89

3.9 Summary and main findings 90

CHAPTER 4 MODEL 2 TEST: AXISYMMTRIC CASE FOR SOIL

INSTALLED WITH A PVD STRIP ‹ - - 5< -<< 119

4.7 Comparison with Model 1 Test -:+sssceseseeseeseessestsenteenaesssenssenesssnesseenses 125

4.8 Scale €ÍẨ€C( -::ecccseessssssececssssssccssssscsesessssscsccessessceseesescseeeeeessseessessssseeenneaeees 127

4.9 Summary and main findings esessesseeceeesseesseeeseesseeestecsteeneesneesanenneenenaes 127

CHAPTERS MODEL 3 TEST : PLANE STRAIN CASE - 142

5.1 Introduction ‹ -: -°-2- << E00 0 g1 0000 142

5.2.1 Apparatus ‹ - cành H0 H0 HH gà HH gi 143

5.2.2 Selection of testing materials -ccensereherrerrirrieriieiiie 143

5.2.3 Preparation of DCM column, -‹ -‹ 5 5-5⁄55<55 55+ 144

5.2.4 Data acquisition system - co csnehhhnhhhhtrererrrrririee 144

5.3 Calibration ig n8 145

5.3.1 Introduction 8 145

5.3.2 1 145

ST .ef 145

5.3.4 Load Cel] ñn 145

5.4 Model preparation procedures -c+eeneriererirreierieirirrrrrer 146 5.4.1 Mounting the first perspex -: +s-c nhe 146 5.4.2 Installation of the bottom plate and PPTS -‹‹-‹ << 146 5.4.3 Setting up the second perspex and strengthening frame - 146

5.4.4 Filling water in the bottom water tank -+e-eesseseseseeeeeeeeseeteesnentens 146

5.4.5 Setting up the bottom geotextile ss-ssccseeeessesseateessesseetensensneeens 147

5.4.6 Pouring clay slurry -‹-‹ ‹ -c-<<csehheehhhhhhhheHhhhien 147

5.4.7 Consolidation of the Clay ‹-‹ -c+ccccestetthieteeihhteiieiiiike 147

5.4.8 Installation of the DCM column ‹ -: : - - <5 <5 S55 119311 1k ee 147

5.4.9 Paving the top sand lay€t - 5s 149

5.4.10 Assembly of the package ‹‹-‹-‹ ‹-c che 149

5.5 Test procedures ‹ ‹ -‹ 5 ch 0x tt rrke 149

5.6 Test results and discussions : -: - - - - -° <5 1S 1H KH kh 150

5.6.1 Bearing capacity ‹ -cccsenneehhhhtHhhhhHhhhh he 150

5.7 Post-test investigations -+-::+sssseeseeeeeeeteeseesenesseseneneesetenseneeneeenens 154

5.7.1 Failure mode - : - - 5+ +11 S931 32101131 3 111111131 kg t1 n1 v4 155

5.7.2 Routine tests on the DCM Columns -:: - - s+sss+sv+ 157

5.7.3 Routine tests on the clay -: : -:-+ +++tsetneehhhhhhehhhhhtrrrerriie 160

5.8 Scale đa on 161

5.9 Summary ‹ -‹ -+ +‹-++* +9 t0 10 H000 H1 0010100 1k 161

CHAPTER6 IMPLEMENTATION OF YIN’S THREE-DIMENSIONAL

ELASTIC VISCO-PLASTIC MODEL IN ABAQUS -: 188

6.1 Introduction he ố.ố.ố.ỐồỐ 188

6.2 Fundamentals of the model - - - - - - - <6 6 6 6 41116161 10 9g ke 188

6.2.1 Basic Formulas - - - =5 << 55221 133311531 S019 HH ky 4 188

6.2.2 Applications of the model -: ‹ ‹-‹ 55-5<5<552c2£eheie 191

6.3 Implementation of the model into FE code ABAQUS - 193

6.3.1 UMAT in finite element code ABAQUS crrressssessessesesstsesteeetteenseeenes 193

6.3.2 Time discretization - - -<- 66 << 5 190119930 9 194

6.3.3 Stress update algorithm -c-cccceshhhehhhhhehHhưe 194

6.3.4 Algorithm modulus -: -5 55 Ằ5< 22% HH0 te 196

6.4 Evaluation of UMAT subroutine ‹-: -: -5- +5 <5} Sư, 197

6.4.1 CU tests sheared at various strain rates -<- 5555 << <2 198

6.4.2 Multi-stage Oedometer test -‹ - Sàn 198

6.4.3 1-D creep test ‹ - + S2 0 00000 tua 198

CHAPTER7 NUMERICAL SIMULATION OF MODEL TESTS - 205

7.2.4 Computed results and comparative studies - 208

7.2.4.1 Consolidation settlement -cc-ssecceeeeceeeeeteeeeseeeeteeeessneeeeees 209

7.2.4.2 Dissipation of eXC€SS POLE DT€SSUT€ -‹<+cc cà 2097.2.4.3 Stress distribution and stress concentration ‹ -: 210

7.2.5 Parametric Studies -ceccescesecsssccesscceseceseecessccsseseesesessesersesesseooaeoes 210

7.2.5.1 Permeability of the DCM column -‹: -‹: + ++°++<*++- 210

7.2.5.2 Viscosity of the soil -‹-‹ -‹ ccccsằecenheeieerereiirirrerde 211

7.3.5.1 Stiffness of the DCM column ‹-: - - <5 55s <s<<<<s<c+><s 215

7.3.5.2 Softening of the DCM column ‹‹-‹-‹ -‹ ‹ - c-5-5<5<5<2<2cczcex 215

7.3.5.3 Viscosity of the soil -cccccceneeieehieheirrierre 216

8.2 Background to numerical modelling -c-c-cscsccecerseiee 250

8.3 Case 1: Bangna-Bangpakong Highway (Bergado et al 1990) ‹‹- - 251

8.3.1 Introduction ‹ -‹ << 55 << 5S S1 vi 251

8.3.2 Mesh design ‹-‹‹ ‹ - 5-5 5S, HH hư 252

8.3.3 Material propertios ‹ - 5-5-5522 0x, 252

8.3.4 Analysis sequence -‹-‹ -‹ -c+ccchhhhHHHHHHH hư 254

8.3.5 Predicted results and comparison with measurements - 2548.3.6 Influence of permeability of DCM column -:-+-+++1ess1eeesstseerseeeseeeereens 2548.3.7 Comparison between EVP modelling and EP modelling - 2558.4 Case 2: Bangkok Test Embankment (Lorenzo 20054) -‹ -<-< << 258

CHAPTER9 CONCLUSIONS AND RECOMMENDATIONS - 280

9.1 Physical modelling -: -‹ - +5 nhi 280

931 Physical model test and field test -: -<-<<< << Ẽ* nhớ nhe,9.3.2 New constitutive models for the cement treated soils -: -

REFERENCES Ẻ90440000000444004006000940000000900922200004200000020000002000004200090002000800050090000%00%660090000900600%000966

Figure 2.2 Chemical reactions between clay, cement, slag and water (after Saitoh et

Al 1985) cesesssssseseseseseseststenetensnenssencneaseeenenenensasssecicacateneneneeeeasesacacasacasasenees 40

Figure 2.3 Performance of different soil improvement techniques (after Ando et al

Figure 2.4 Environmental impact of various ground improvement techniques: (a)

noise effect; (b) effect of vibration during construction (after Ando et al

Figure 2.5 Plane layout of different improvement patterns of DM method (after

Coastal Development Institute of Technology 2002) -++++:ssereesteteeeees 42Figure 2.6 Different improvement patterns of DM method (after Coastal

Development Institute of Technology 2002) -: -: -‹-‹-5-5<2<c<c+ceeree 44

Figure 2.7 Barge for marine works and equipment for on land works (after Endo

Figure 2.8 Typical stress-strain of cemented soil (after Endo 1976) - 45Figure 2.9 Effects of cement content on unconfined compressive strength of cement

treated soil (after Uddin 1995; Uddin et al 1997) -<=- 46Figure 2.10 Effects of age on unconfined compressive strength of cement treated soil

(after Endo 1976) ‹-‹ -c- St HH Hee 46

Figure 2.11 Effects of initial water content of the soil on unconfined compressive

strength of cement treated soil (after Endo1976) -‹<-+ <‹ 47Figure 2.12 Effects of curing temperature of the soil on unconfined compressive

strength of cement treated soil (after Kawasaki et al 1981) - 47

Figure 2.14 Relationship between unconfined compressive strength of laboratory

treated soil and in-situ treated Soi] - - <5 Sen ve 49

Figure 2.15 Scale effect on unconfined compressive strength (after The Building

Center of Japan 1997) ‹ -c- sen HH re 50

Figure 2.16 Relationship between Eso and qg, for cement treated Hong Kong marine

clay (after Yin and Lai 1998) ‹ -:.-‹ -5 5c nhe 50

Figure 2.17 Relationship between void ratio and consolidation pressure for laboratory

tests on cement treated Bangkok clay for 1 month curing time (after

Uddin 8.11 0011 Ốc 51

Figure 2.18 Relationship between void ratio and consolidation pressure for laboratory

tests on cement treated Bangkok clay for 5% cement content (after

Uddin et al 1997) sesssessesseseseseseeeserenssesnssesssseneeesersessseesensssssensiseneneeas 51

Figure 2.19 Relationship between void ratio and consolidation pressure for field

samples of cement treated soil (after Sugiyama et al 1984) - 52Figure 2.20 Relationship between void ratio and consolidation pressure for cement

treated reconstructed Hong Kong marine clay samples (after Cheung

Figure 2.21 Coefficient of volume compressibility and coefficient of consolidation

obtained form the oedometer tests (after Cheung 2003) - 53Figure 2.22 Results of CU tests for 5% and 15% cement content (after Endo 1976)

Figure 2.25 Generalized stress behaviour in (p, g) space (after Bergado et al 1996;

Uddin 1997) ‹‹ -. - 5c nh nh HH Hà 58

Figure 2.26 Results of CU tests on cement treated Hong Kong marine clay with

initial cement content 15% (after Cheung 2003) -‹eesằ 60Figure 2.27 Results of CU tests on cement treated Hong Kong marine clay with

initial cement content 20% (after Cheung 2003) -+cennneee 62Figure 2.28 Relationship between permeability and water content of cement treated

soil (after Terashi et al 1983) s-ssssseseseseeseeesseseseeneeetsessssseasseneneneseneeens 63

Figure 2.29 Schematic diagram of the newly developed permeameter for cement-soil

mixture (after Yu et al 1999) ‹ - cào ninh 64

Figure 2.30 Schematic diagram of the apparatus for measuring the permeability of

cement-soil mixture (after Kawasaki et al 1981) -‹+reeee 65Figure 2.31 Variation of coefficient of permeability with cement content for

laboratory and field samples (after Porbaha et al 2000) - 66Figure 2.32 Variation of coefficient of permeability of cement treated marine clay

(after Chew et al 2004) sesseseeseeseeetetesssesressseeneenesrenssestensseseeneeseetess 67

Figure 2.33 Typical failure modes of the DM ground (after Bergado et al 1996)

Figure 2.34 The failure mechanism with five blocks (a) cross section and (b) plane

view (after Bouassida and Porbaha 2004) cee c eee n neces enn neeeseseaeeneseesecaeecees 68Figure 2.35 Axisymmetric “unit cell” model of DCM column surrounding by soil

dimensional model for treated soil; (b) stresses on the treated soil; (c)

stresses on the untreated Soil - - 55 5 S1 1 9 ngư 69

Figure 2.37 Sketch of the unit cell (after Xie and Xie 2001) -+cccccằe 70Figure 2.38 Possible failure modes for single columns (after Broms 2000) - 70Figure 2.39 Progressive failure in the soil ground (after Broms 2000) - 71Figure 2.40 Model setup (after Kitazume et al 1996; Kitazume and Yamamoto 1998)

Figure 2.41 Failure pattern of the improved soil ground (after Kitazume et al 1996;

and Kitazume and Yamamoto 1998) ẨẨ- 73

Figure 2.42 Grain-size distribution curve for Hong Kong marine clay (after Yin and

Lai 1998; Zhu and Yin 2000) "—- 73

Figure 2.43 Locatlons of samples 4đđ®°ed0°00đ609A09049000006969040960090 0000096290029 00900194 0044940494 4204049090449060090049000429006090060420 1 74 Figure 3.1 Apparatus for the model test «vrcrrcsscccececsssrserecsnesescersnsscseseneesnessssenenereseees 91Figure 3.2 Schematic diagram of the model test and locations of instruments in the

model: (a) a vertical cross-section view of positions of varioustransducers and (b) a horizontal view of positions of various transducers(note: the first number in brackets means the radial distance and thesecond means distance from the bottom in mm) -‹ -:+:°*++++*s+ceeeeere 92Figure 3.3 Particle size distribution curve of Hong Kong marine clay used in the test

¬ 93

Figure 3.4 Calibration curves for PPT§ ‹-‹ -5-5 che 95

Figure 3.5 Calibration curves for LVDTSs -5-522ccnehthhhhhhhrhhrrerrrree 96

Figure 3.6 Calibration curves for EPCs -++++:::ssssseesesseseeesseeseseeneseeseesseneseseensseeneenes 96

Figure 3.9 Mixing of marine clay by motorized rotary Mixer -:: *****sssssssc 98Figure 3.10 Preconsolidation of clay for the model ground - 98Figure 3.11 The procedures of installation of DCM column «+++++++++++sssseereeeseeeeeereeenes 99Figure 3.12 Final model ground consisting of preconsolidated USC and a DCM

column in the cylinder mold 99444940444604449040440440904490092440004400999494240604409006001940900 003096060666 99

Figure 3.13 Layout of a top sand layer (drainage) and two earth pressure cells - 100Figure 3.14 Two LVDTs assembled on the top of the model to measure the surface

settlemetni( -: -***9 nhì kh» ng nh Hà hà HH senses 8 10 1400 01 6 1 156 100

Figure 3 1 5 Applied vertical loading history ÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔÔ ÔÔ 101

Fi gure 3.16 Measured settlement With time ‹ : :-‹ -‹-<-22+22<% %1 t1 ng nến kg ky 101

Figure 3.17 Variations of excess pore water pressure with surcharge on the clay

under the first loading -: -°+°cn+nnnhnhhhhnHHHH HH 102

Figure 3.18 Variations of excess pore water pressure with surcharge on the clay

under the second loading -‹ - 555 103

Figure 3.19 Variations of excess pore water pressure with surcharge on the clay

under the third loading - 5-5 nh 104

Figure 3.20 Variations of excess pore water pressure with surcharge on the clay

under the fourth loading -: -5-5-5sSsnenhnhhttnhhhrrrerrree 105

Figure 3.21 Vertical profile of excess pore water pressure with time under the first

loading - «s55 HH HH HH n0 tán ke 106

Figure 3.22 Vertical profile of excess pore water pressure with time under the second

loading ằẰằ G 1H Ỏ 106

Figure 3.24 Vertical profile of excess pore water pressure with time under the fourth

loading -ccennhnnhht nhe HH HH Hà tt ri 107

Figure 3.25 Radial profile of excess pore water pressure with time under the first

Figure 3.28 Radial profile of excess pore water pressure with time under the fourth

Figure 3.29 Stresses shared by DCM column and USC and stress concentration ratio

with time throughout the physical modeling test -cằ 110Figure 3.30 Relationships between stress concentration ratio and degree of

consolidation versus time throughout the model test - 112

Figure 3.31 Failure mode of the DCM Column ‹ :-: - -= << $1⁄1 1n nY Y9 v 113

Figure 3.32 Arrangement of soil sampling After test -;=<s* He nh khe, 115Figure 3.33 Pressure versus volume strain curves for three soil samples obtained

from Oedometer tests hố 116

Figure 3.34 Variations of permeability with void ratio for soil samples: (a) Log(&)

versus Log(e) curve; (b) Log(A) versus é CUYV€ ++i 117

Figure 3.35 Results of CU tests: (a) g versus axial strain curve; (b) u versus axial

Strain CUIVE; (C) D'~ G CUYV€ -*°+-+++sshhhhhhhhhnhthhhrttrdrrrerrrrrrrirrrie 118

the radial distance in mm from the center and the second one is thevertical distance in mm from the bottom of the soil body) - 128

Figure 4.2 Calibration curves for PPTs -‹ -sccc che 130

Figure 4.3 Calibration curves for LVDTSs -+-+++++1:sssessesesseesseeeseseeseseeneseereeeeneseeneneaens 131

Figure 4.4 Set up and orientation of PPTs before preconsolidation stage - 132Figure 4.5 Simulation of in-situ installation process Of PVD ‹‹‹ -‹‹ ‹ccchhinnnneee 132

Figure 4.6 Applied vertical loading history -++++ +1s sees sen 133

Figure 4.7 Measured settlement with time +-++-+ 1+::1seesseessecesseeesesesseeeeseseeeeeneecenans 134

Figure 4.8 Variations of excess pore water pressure at PPTs under the total vertical

load 20 kPa (from 15 kPa to 20 kPa) se++-ssssssesseseesteeeetseneseereseenesceneneeens 134

Figure 4.9 Variations of excess pore water pressure at PPTs under the total vertical

load 40 kPa (from 20 kPa to 40 kPa) -: - 5-5-5 sành 135

Figure 4.10 Variations of excess pore water pressure at PPTs under the total vertical

load 60 kPa (from 40 kPa to 60 kPa) -++++1+ssssseseeseseereesteseeeacseseeeenereenes 136

Figure 4.11 Dissipation of excess pore pressure at different PPTs for Model 1 test

and Model 2 test with the surcharge on the soil under the first loading

increment (from 20 kPa to 40 kPa) -: -c: che 137

Figure 4.12 Dissipation of excess pore pressure in the vertical and horizontal

directions at different PPTs for Model 1 test and Model 2 test under thesecond loading increment (from 20 kPa to 40 kPa) -s> 138

and Model 2 test with the surcharge on the soil under the second loading

increment (from 40 kPa to 60 kPa) ‹ -:-5:5ccnnenhnhhhhnhHhehke 140

Figure 4.14 Dissipation of excess pore pressure in the vertical and horizontal

directions at different PPTs for Model 1 test and Model 2 test under the

second loading increment (from 40 kPa to 60 kPa) - 141Figure 5.1 Engineering background of the model test « -++::1+::s:e+eeeeeseeeereneenees 164

Figure 5.2 Apparatus for Model 3 test ovrrcrrsscrceccrsesscccerescsrssensvsnceseccrenesssrsnsnseneeeeeens 164

Figure 5.3 Schematic diagram of Model 3 and locations of instruments in the model:

(a) a horizontal view of positions of various transducers (b) a verticalcross-section view of positions of various transducers and - 165Figure 5.4 A hydraulic jack and a reaction system employed in the test - 166

Figure 5.5 Calibration curves for PPTs (four PPT) «:+1sssssssseseesessetesrsesseceeneesesees 167

Figure 5.6 Calibration curves for EPC ‹-‹ -cc che 168

Figure 5.7 Calibration curves for load cell -:-++:-1: eset trseeseereeeeseeneseeteneneateneneeceney 168

Figure 5.8 Installation of PPTs on the bottom permeable plate -+ -+ +++-:1s+esereeeeees 169Figure 5.9 Saturated geotextile and PPTs at the bottom of tank before pouring clay

Figure 5.11 A guiding system to control the perpendicularity of the columns - 170Figure 5.12 Details of installation of DCM columns -: -: ++c++**s‡ece+++ss 172Figure 5.13 Vertical pressure versus vertical displacement relationship - 173Figure 5.14 Changes in excess pore pressure in the fourth stage of Subtest 1 - 173

— 175

Figure 5.18 Numbering of DCM columns -: - 555-555 55S+snnetethehererieirerire 175

Figure 5.19 Deformed surface of model foundation ‹ -‹ -5-5- + 176

Figure 5.20 Failure of the DCM columns in the model foundation - 179Figure 5.21 Generalized slip plane along the axes of columms - 180Figure 5.22 Schematic stress paths for elements 1n the DCM columns - 180Figure 5.23 DCM columns excavated after the completion of test - 181Figure 5.24 Stress ~ strain curves of the columns from UC test - 181Figure 5.25 Triaxial shear stage data: (a) Stress ~ axial strain curves of the columns

from CU test; (b) Pore water pressure ~ axial strain curves of thecolumns from CU test; (c) Stress paths plots from CU tests - 183Figure 5.26 Undrained behaviour of cement treated Bangkok clay (after Bergado et al

1996; Uddin 1997) ‹-‹-. - con nưke 183

Figure 5.27 Undrained behaviour of cement treated Hong Kong marine clay - 184Figure 5.28 Soil for sampling after treated section removed : -+ -++<e«+eeeeee 184Figure 5.29 Vane shear and the average undrained shear strength - 185Figure 5.30 Vertical pressure versus volume strain curves for two clay samples

Obtained from Oedommeter tests -recrereceecrercervececsrecesccrvrerevsenreeerssseeesees 186

Figure 5.31 Creep curves for two clay samples obtained from oedometer tests - 186

versus Log(e) curve; (b) Log(&) V€FSUS € CUYV€ :-++*++t°*sé hen kh he hớ 187Figure 6.1 The inclined elliptic flow surface adopted in the EVP model - 201Figure 6.2 Mesh and boundary conditions for triaxial tests -++:+++-:+++esseesereeeeeeeeeetees 201Figure 6.3 Comparison between measurements and predictions for CU tests: (a) q~&

relationship curve; (b) u~& relationship curve; (c) p’~q relationship curve

Figure 6.5 Comparison between measurements and predictions for multi-stage

oedometer tests: (a) & ~ time relationship curve; (b) & ~ p’ relationship

Figure 6.6 Comparison between measurements and predictions for 1-D creep test: (a)

& ~ time relationship curve; (b) & ~ p’ relationship curve -‹ - 204Figure 7.1 Mesh and boundary conditions used in the numerical simulation with

monitored points (PPTs) for Model 1 test :-:-:s:sssssseseesesseseeeseeeeeseesees 220

Figure 7.2 Mohr-Coulomb failure criterion in FE meridional plane (after ABAQUS

User’s and Theory Manuals, 2001) -: -‹ 5-5+ 52s 221

Figure 7.3 Yield surface in the meridional plane and deviatoric plane (after

ABAQUS User’s and Theory Manuals 2001b) - -©-©5- 221

Figure 7.4 Mohr-Coulomb flow potential in meridional plane (after ABAQUS User’s

and Theory Manuals 2001b) +-+-:+:sssssseseeseeeeeeeeeeesneneensnesneneeneeateneeees 222

Figure 7.5 Mohr-Coulomb flow potential in deviatoric plane (after ABAQUS User’s

and Theory Manuals, 2001a) ố- 222

Figure 7.8 The softening pattern used in the analysis (b = 20.0) :++-::++ereeesereeeeerteees 224Figure 7.9 Computed and measured settlements with time -‹++sceen 224Figure 7.10 Computed and measured excess pore pressures at different PPTs - 226Figure 7.11 Computed and measured stresses carried on the DCM column and the

soil throughout the teSt - nh} nén nh ng kh nà tà ty nh Y0 kh 227Figure 7.12 Computed and measured stress concentration ratios throughout the test

Figure 7.13 Influence of the permeability of DCM column on the consolidation

settlement PPPSSTTETELISETELISTISIT ELE SETET TTT T STEP 0 0 6 4949.66.46.44 9.404.496 4 0 64.0.4046 0.406.046 6 6-8 6.60 0/4 có Đồ Đ Đo Đo 000 4.0.0 9 228Figure 7.14 Influence of the permeability of DCM column on excess pore pressure

Figure 7.15 Influence of the viscosity of the soil on the stress distribution and stress

transferring "ằ- 232Figure 7.16 Influence of the permeability of DCM column on the stress concentration

Figure 7.18 Influence of the viscosity of the soil on the excess pore pressure - 237Figure 7.19 Enlarged humps of pore pressure for different viscosities of the soil

Figure 7.20 Influence of the viscosity of the soil on the stress distribution and stress

transferring - H 239

Figure 7.22 Mesh and boundary conditions used in the numerical simulation for

Model 3 test - nành he nh nh th t1 3:60 n1 0 eran ses 1 1221 186 241

Figure 7.23 Experimental and simulated results of CU triaxial tests on the DCM

columns excavated from the soil ground in Model 3 test - 242Figure 7.24 Computed and measured load versus displacement curves -: - 242Figure 7.25 Shadings of PEEQ obtained in the amalysis -‹ -+-+++etrrreerrrreerrrer 243Figure 7.26 Effect of the stiffness of the DCM column on the load versus

displacement CUFV€ - 55-5-5222 Hieg 243

Figure 7.27 Three types of different softening modes for the DCM columns - 244Figure 7.28 Effect of the softening pattern of the DCM column on the load versus

Bergado et al 1990) -:-ses:sesesesseees seers nee reesesnesrenrseesseerssseseeeseeneseeeseenes 263

Figure 8.3 Rehabilitation scheme for Banga-Bangpakong Highway using DMM

ground improvement (after Bergado et al.1999) :-++:seeseesseeerreeeeeeenes 264

Figure 8.4 Undrained shear strength contours along highway (after Pussayanavin and

Leerakomsan 1986) s +-sssssssesessesesseeeeeeseseessessseeseeseesseenssteneseeneessasaeseanens 265

Figure 8.5 Water content contours along highway (after Bergado et al.1990) - 265 Figure 8.6 Compressibility characteristics at different sections along highway (after

Bergado et al.1990) "ằ 266

Figure 8.8 Undrained shear strength of cement columns constructed at four different

sections on Bangna-Bangkong Highway (after Bergado et al.1990) - 268Figure 8.9 DCM pile unit cell used in the axisymmetric analysis and soil profile for

Case 1: station 29+950 (not to scale) ‹‹ -‹ -s che 269

Figure 8.10 Mesh and boundary conditions used in the numerical simulation - 270Figure 8.11 Main strata and initial stresses in the numerical simulation - 271Figure 8.12 Loading history and simplified loading mode for Case 1 - 271Figure 8.13 Predicted and measured settlements with time ‹ -:-: -:-‹ +++*see 272Figure 8.14 Coefficients of permeability of cement treated Bangkok clay from

consolidation tests (after Lorenzo 2001) -1 -rssseeeeseeeseeeseseereseseenenens 273

Figure 8.15 Influence of the coefficient of permeability of DCM column on

nEn n 274

Figure 8.16 Influence of the coefficient of permeability of DCM column on excess

OT€ Df€SSUF€ oe tre se 274

Figure 8.17 Comparison between MCC model and the present EVP model - 275Figure 8.18 Relationship between ej and [- *s“ttnhnttt tt n2 123493114 4010201213 SS 276Figure 8.19 Comparison between the predicted settlements from EVP model and

I (@ em 1 276

Figure 8.20 Test embankment near the EGAT Power Station Site at Amphur

Wangnoi of Thailand (after Lorenzo 2005) ++++++receesessseeeteetttteeeeeees 277Figure 8.21 Subsoil at the site of Case 2 (after Lorenzo 2005a) -c+ằ 277

Figure 8.23 Plane view of the test embankment of Case 2 (after Lorenzo 2005a) 278Figure 8.24 Longitudinal cross-section of Case 2 (after Lorenzo 2005b) - 279Figure 8.25 Transverse cross of Case 2 (after Lorenzo 2005a) -eeeiieee 279Figure 8.26 Mesh and boundary conditions used in the numerical simulation with

monitored points P7⁄3 and P6/6 - -s* SH 1kg nhu KH kh hi 6 280 Figure 8.27 Initial stress field used in the analysis = 281Figure 8.28 Loading history and simplified loading model for Case 2 - 281Figure 8.29 Predicted and measured settlements on the DCM column surface - 282Figure 8.30 Predicted and measured settlements on the soil surface - 282Figure 8.31 Predicted and measured excess pore pressures at depth 3 m - 283Figure 8.32 Predicted and measured excess pore pressures at depth 6 m - 283

— 35

Table 2.2 Factors affecting the strength increase (after Terashi 1997) - 37Table 2.3 Relationships between E59 and gy from different studies - 37Table 2.4 Relationships between py and gu from different studies - 38

Table 2.5 Different failure modes for single column -: - ‹ 5-55°5<c+c+c<se<ceceere 38

Table 2.6 Chemical composition of the three samples (after Tovey 1986) - 39Table 2.7 Typical mechanical properties Hong Kong marine clay (after Koutsoftas et

al 1987; Zhu and Yin 2000) ‹-‹ - 5-1 39

Table 3.1 Basic properties of HKMC used in this test -55Scccsscerseieeeeeere 91

Table 3.2 Summary of sampling and soil parameters from the tests - 91Table 5.1 Summary of sampling and soil parameters in the post-test -«- 163Table 5.2 Comparison between two improved soil grounds ‹ -cc++> 163

Table 6.1 Parameters used in CU tests - - - - 5 25 S13 190 19H HH ng kg 200

Table 6.2 Parameters used in multi-loading oedometer tests -‹©©<-< 200

Table 6.3 Parameters used in 1-D creep tests -+-c-srneeenhhtereeiriiiiree 200

Table 7.1 Material parameters for the soft soil used in the FE analysis for Model 1

Table 8.2 Material parameters for other soil layers and DCM column used in the FE

analysis for Case 1] -‹ : -ssseenhhhhhhhhhhhhhhHrrrrrrriririirrrirrree 261

Table 8.3 Material parameters for the Modified Cam-Clay model used in the FE

analysis for Case 1 s-sesesesesseseeeeseeseesesesresesesenesneeseasensseeeseneenseneesnaeieey 262

Table 8.4 Material parameters for soils used in the FE analysis for Case 2 - 262Table 8.5 Material parameters for DCM column used in the FE analysis for Case 2

1.1 Background

Due to the increasing growth in the infrastructure of urban and metropolitan areas inthe most countries of the world, it has been really difficult to find the appropriateground for building these structures As a result, the construction of numerousmegaprojects on soft deposits is indispensable The remedial solution to overcome theconstruction difficulties on poor quality ground is either to improve the highlycompressible soils or to install deep foundation Improvement techniques are usuallymore cost-effective compared to deep foundation method One of soil improvementmethods, Deep Mixing (DM) method has been frequently applied to improve soft soilground since it was initiated about three decades ago, in Japan by the Port andHarbour Institute and in Sweden by the Swedish Geotechnical Institute (Porbaha1998) In this technique, chemical stabilization agents such as Portland cementpowder or cement slurry are used to mix with in situ soft soil to form columns in theoriginal soil ground using the specially designed machine When cement power orcement slurry is used, this technique may also be called as Deep Cement Mixing(DCM) method The methods of mixing generally applied in the installation of deepmixing columns in the soil ground are either mechanical mixing or high pressure jetmixing / grouting (Kamon and Bergado 1996) In the mechanical mixing, thechemical agents are mixed into the soil by mixing blades; while in the jet mixing, theagents are mixed into the soil through jet of water or slurries of agents

A large number of laboratory tests on the cement treated soil had been carried out inthe past decades (Broms 1979, Kawasaki et al 1981; Terashi and Tanaka 1983;

Tanaka and Terashi 1986; Kamon and Bergado 1991; Walker 1994; Kamaluddin and

Balasubramaniam 1995; Schaefer et al 1997; Yin and Lai 1998; Lin and Wong 1999;

Fang et al 2001; Porbaha et al 2000; Porbaha 2002; Tan et al 2002; Horpibulsuk et

al 2004b) However, most of the work has been confined to the strength and stiffness

of the cement mixed soil To date, little attention has been devoted to theconsolidation behaviour of the treated soil ground by this method (Terashi and Tanaka1983; Lorenzo and Bergado 2003) To better understand the consolidation mechanismand process of the improved soil ground using DM method, it is desirable to carry outmany laboratory small-scale physical model tests or full-scale field tests with fullinstrumentation to record the full consolidation process The results obtained arevaluable for understanding the consolidation process and influence factors as well forverifying existing analytical solutions and numerical models Unfortunately, full-scalefield tests are expensive and only a small number of such tests have been done andreported in the literature Therefore, laboratory physical model tests with fullinstrumentation are a preferred approach

The permeability of the cement treated soil has been found to be relatively higher thanthat of untreated soil (Lorenzo 2001; Cheung 2003; Chew et al 2004), which leads us

to infer that the DCM column might function as effective drain in the DCM treatedsoil ground However, to date, no experimental evidence has been reported to supportthis inference In this case, laboratory physical model tests are requisite to clarify ifthe DCM columns work like drains, and if they do, what is the difference from theconventional vertical drains

1998; Kitazume et al.1999) analysed the improved soil grounds treated by a DCMcolumn group In their studies, the purpose of model tests has been restricted to theinvestigation of bearing capacity of this kind of improved ground More data of porepressure and more investigations into the stresses distribution and transferring are notavailable However, it could be useful to study pore pressure responses and stressdistribution and transferring for understanding the performance of the improvedground.

Various failure modes of the improved soil ground installed by a DCM column group,shear, bending, tensile failures and rupture breaking have been summarized depending

on ground soil properties, external loading and also the locations of each column(Miyake et al 1991; Hashizume et al 1998; Kitazume et al 2000) However, it is clearthat the failure pattern of the improved soil ground may be subject to many factors.Possibly, there are still some factors which have not been identified Therefore, moremodel tests are still worthy to explore the potential and unknown influencing factorsand failure patterns of the improved soil ground

Two simple analytical approaches have been proposed to estimate the vertical bearingcapacity of the improved soil ground by DCM methods (Bergado et al 1996 andBroms 2000) Bouassida et al (1995) and Bouassida and Porbaha (2004) developed alower bound and an upper bound of the bearing capacity of end-bearing column groupreinforced ground according to limit analysis theorem However, there is a clear needfor a great deal of experimental data to validate these methods Furthermore, theassumed failure model adopted in each method also requires experimental evidence