Effects of tunnel construction on nearby pile foundations 1

THE EFFECTS OF TUNNEL CONSTRUCTION ON NEARBY PILE FOUNDATION PANG CHIN HONG NATIONAL UNIVERSITY OF SINGAPORE 2006... THE EFFECTS OF TUNNEL CONSTRUCTION ON NEARBY PILE FOUNDATION PANG

THE EFFECTS OF TUNNEL CONSTRUCTION ON NEARBY

PILE FOUNDATION

PANG CHIN HONG

NATIONAL UNIVERSITY OF SINGAPORE

2006

THE EFFECTS OF TUNNEL CONSTRUCTION ON NEARBY

PILE FOUNDATION

PANG CHIN HONG

(B.Eng (Hons.), Manchester)

A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY

DEPARTMENT OF CIVIL ENGINEERING NATIONAL UNIVERSITY OF SINGAPORE

2006

DEDICATION

To my dearest parents and sister

i

To my co-supervisor, Prof Chow Yean Khow, who had throughout the research, gave me very constructive comments without which this thesis will not be so valuable I thank him for his willingness to share his experience and guidance

Not to be forgotten, my former supervisor, Dr Dasari Ganeswara Rao who had left for the United State He had closely supervised my work for the first three semesters and had given me pragmatic advice and guidance on finite element modelling, ABAQUS software and SDMCC model

Besides, I also appreciate the advice from A/Prof Leung Chun Fai in the constant students group discussion held every forth-night Gratitude also goes to A/Prof Somsak Swaddihipong and A/Prof Tam Chat Tim of the Structural Group in NUS for their advice on issues related to structure and concrete

For case study on the MRT North East Line Contract C704, special thanks has to be delivered to

Dr Jeffrey Wang, formerly chief engineer at MRT NEL C704, Dr Lim Ken Chai of Tritech Consultant Pte Ltd for providing valuable field data, constant correspondence and discussion In addition, data were also obtained from the Land Transport Authority (LTA) of Singapore with the permission from Mr Rajan Krishnan, former Project Director Not to be missed, LTA staff who has taken a great time and effort to dig out the data for me, particularly Mr Seetoh Hon Hoy and Mr Azmi Aidi

For case study on the MRT Circle Line C825, thanks go to WH–STEC-NCC JV for providing the

field data and allowing assess to the construction site, particularly Mr Chu Chiang Yong,

Coordination Manager, Mr David Lee, Geotechnical Manager, Mr Yang Hong Qiang,

Geotechnical Engineer and Mr Nigel Ogden, Tunnel Construction Manager, Mr Lim Han Chong,

Senior Engineer and Mr Savaranan, QA/QC Engineer

Furthermore, I thank Dr Jeffrey Wang of Tritech Consultants and Dr Jeyatharan Kumarasamy of

LTA for spending their precious time to review my thesis and feedback

Besides, I extend my appreciation to my many colleagues and friends who I have consulted during

the course of the research, particularly Ch’ng Yih, Cheh Hsien, William Cheang, Zou Jian,

Dominic Ong, Hai Bo, He Lin and Ah Lee To my two buddies, Kar Lu and Kheng Ghee who have

been with me for lunch and dinner almost every day, I greatly enjoy your companion and also the

trips we had together especially to Vietnam Not without which the heartiest support from Magenta

Sim, a dear friend who keep me accompanied at all time

Last but not least, thanks to National University of Singapore for the award of research scholarship

throughout the four years period without which this research program would not has commenced

TABLE OF CONTENTS

DEDICATION i

ACKNOWLEDGEMENTS ii

TABLE OF CONTENTS iv

NOTATIONS x

LIST OF TABLES xiii

LIST OF FIGURES xiv

LIST OF PUBLICATIONS xx

SUMMARY xxi

CHAPTER 1 INTRODUCTION 1

1.1 Background……….……… 1

1.1.1 Tunnel construction near pile foundation……… ……… 2

1.1.2 Current design and construction approach……… …… 3

1.2 Objectives of the study……… ……… 4

1.3 Organisation of thesis… ….……… ….……… 6

CHAPTER 2 LITERATURE REVIEW 8

2.1 Introduction ……… 8

2.2 Pile responses caused by tunnelling: Physical observations.……… … 9

2.2.1 Case histories.……… 9

2.2.2 Laboratory and centrifuge tests ………… ……… 12

2.2.3 Full scale pile tests……… ……… 15

2.3 Pile responses caused by tunnelling: Prediction and design methods.… 16

2.3.1 Empirical method……… 16

2.3.2 Finite element method….……….……… 17

2.3.3 Numerical and analytical methods.………… ……… 19

2.3.4 Design charts……….……… 21

2.4 Current understanding and outstanding issues.….……… 21

2.4.1 General……… 22

2.4.2 Pile settlement……… 22

2.4.3 Pile axial force……… 23

2.4.4 Pile lateral deflection……… ……… 24

2.4.5 Pile bending moment……… 24

2.4.6 Pile group effect……… ……… 25

2.4.7 Multiple-tunnel advancement effect……… ……… 26

2.5 Concluding remarks……….……… 26

CHAPTER 3 CASE STUDY: TUNNELLING ADJACENT TO PILE FOUNDATION 27

FOR THE CONTRACT C704 – GROUND CONDITION AND FIELD

MONITORING 3.1 Introduction……… 27

3.2 Background and overview of the project……… …… 28

3.3 Geology and ground conditions ….……… 29

3.4 Design and construction details……… 30

3.5 Construction sequence……… 33

3.6 Instrumentation programme.……….……… 34

3.6.1 Monitoring scheme………… ……….……… 34

3.6.2 Interpretation of data….……….……… 35

3.6.2.1 Assessment of surface settlement……… 35

3.6.2.2 Assessment of instrumented pile……… 35

3.7 Monitoring results……… 37

3.7.1 Ground surface settlement……… 37

3.7.2 Subsurface soil movement……… 40

3.7.2.1 Vertical soil movement……… 40

3.7.2.2 Lateral soil movement……… 41

3.7.3 Response of pore pressure… ……… 43

3.7.4 Responses of pile foundation……… 43

3.7.4.1 Tunnelling induced axial force……… ……… 43

3.7.4.2 Tunnelling induced transverse bending moment……… 46

3.7.4.3 Tunnelling induced longitudinal bending moment……… 48

3.7.4.4 Post-tunnelling loading on piles……… 49

3.7.5 Relationship between soil movement and pile responses ……… 50

3.7.5.1 Axial force vs volume loss……… 50

3.7.5.2 Bending moment vs volume loss……… ……… 51

3.7.5.3 Transverse BM vs longitudinal BM……… 52

3.7.5.4 Distance effect vs pile group effect……… 52

3.8 Analysis of pile responses using design charts proposed by Chen et al (1999) …… 53

3.9 Concluding remarks……… 55

CHAPTER 4 CASE STUDY: TUNNELLING ADJACENT TO PILE FOUNDATION 57

FOR THE CONTRACT C704 – THREE-DIMENSIONAL FINITE ELEMENT ANALYSIS 4.1 Introduction……….……… 57

4.2 Current three-dimensional modelling techniques……… 58

4.2.1 Modelling of shield tunnel advancement……… ……… 58

4.2.2 Modelling of pile foundation……… 61

4.3 Details of analysis……… ……… ……… 61

4.3.1 Finite element mesh and boundary conditions……….……… 61

4.3.2 Numerical modelling procedure……… 63

4.3.3 Ground conditions and soil profile……… 65

4.3.4 Material constitutive models……….……… 65

4.3.5 Soil parameters for analysis……….……… 68

4.3.5.1 General soil parameters……… 68

4.3.5.2 Parameters for Mohr-Coulomb model……… 68

4.3.5.3 Parameters for MCC model……… 68

4.3.5.4 Parameters for SDMCC model……… 69

4.3.6 Tunnelling parameters for analysis……… 72

4.3.7 Pile parameters for analysis……… 73

4.4 Analysis of greenfield soil movement due to tunnel advancement ……… 73

4.4.1 Effect of tunnelling advance rate….……… ……… 74

4.4.2 Effect of face pressure……… 75

4.4.3 Effect of tail void grouting……… 76

4.4.4 Effect of lining stiffness ……… 79

4.4.5 Effect of soil models……… 79

4.4.6 Effect of soil earth pressure at rest (Ko)……… 80

4.4.7 Controlling tunnel convergence by artificial boundary conditions……… 81

4.5 Analysis of pile responses subjected to single tunnel advancement…… 83

4.5.1 Results of a typical analysis……… 83

4.5.2 Effect of tunnel face pressure……… 86

4.5.3 Effect of pile cap and pile cap fixity ……… 87

4.5.4 Effect of pile stiffness……….…….……… 88

4.5.5 Effect of soil earth pressure at rest (Ko)……… 88

4.5.6 Effect of pre-tunnelling loading in piles……… 89

4.6 Analysis of pile responses subjected to post-tunnelling construction ……… 90

4.7 Comparison of pile group analysis to single pile and greenfield analyses……… 92

4.8 Analysis of pile responses subjected to twin-tunnel advancement….… 93

4.9 Concluding remarks……… ……… 95

CHAPTER 5 PARAMETRIC STUDIES OF PILE RESPONSES DUE TO TUNNELLING 97

5.1 Introduction……… 97

5.2 Simplified three-dimensional finite element model ……….………… 98

5.2.1 Soil model and parameters……… 98

5.2.2 Numerical simulation procedure……….… 99

5.2.3 Modelling the pile-soil interface……….……… 100

5.2.4 Details of parametric studies ……… 102

5.3 Results of parametric studies ……… … …… …… 103

5.3.1 Pile settlement……… 103

5.3.2 Pile axial force……….……… 104

5.3.3 Pile lateral deflection……… ……… 107

5.3.4 Pile bending moment……… 107

5.4 Effect of pile shaft de-bonding……… 108

5.5 Effect of pile group ……… 110

5.5.1 Effect of pile group size……… 111

5.5.2 Effect of pile group layout…….……… 113

5.6 Concluding remarks……… ……… 113

CHAPTER 6 PLANE STRAIN IDEALISATION OF TUNNEL-PILE INTERACTION 116

IN FINITE ELEMENT ANALYSIS

6.1 Introduction……… 116

6.2 Current plane strain modelling techniques for tunnel and pile foundation……… 117

6.2.1 Modelling of tunnel……… 117

6.2.1.1 Technique 1: Gap method……… 118

6.2.1.2 Technique 2: Convergence confinement method……… 118

6.2.1.3 Technique 3: Volume loss control method……… 119

6.2.1.4 Technique 4: Progressive softening method……… 119

6.2.2 Modelling of pile foundation……….……… 119

6.2.2.1 Technique 1: Modelling soil and structural material as a composite element……… 120

6.2.2.2 Technique 2: Modelling soil and structural material as a continuous element……… 121

6.2.2.3 Technique 3: Modelling structural material as an external element ……… 121

6.3 Techniques to be adopted in this study…… ……….…… ….……… 122

6.4 Single pile response due to tunnelling.…… … … ……….………… 125

6.4.1 Problem definition………… ……… 125

6.4.2 Details of analysis………….……… 126

6.4.3 Typical results of analysis.……… 127

6.4.4 Effect of pile-soil interface… ……… 129

6.4.5 Effect of soil stiffness……… ……… 131

6.4.6 Effect of tunnel volume loss……… 132

6.4.7 Effect of pile stiffness….….……… 133

6.4.8 Effect of pile diameter……… 133

6.4.9 Effect of pile-tunnel distance……… 134

6.4.10 Effect of pile length to tunnel depth ratio……… 134

6.4.11 Effect of loading acting on pile……… 135

6.5 Pile group response due to tunnelling.……… ……… 137

6.5.1 Idealisation of single-row pile group.……… 137

6.5.2 Idealisation of multiple-row pile group…….……… 138

6.5.3 Effect of pile spacing……….……… 138

6.5.4 Effect of pile rows spacing……… 139

6.5.5 Effect of pile group size……… 139

6.5.6 Effect of pile cap……… 140

6.6 Calibration charts and recommendations……… 140

6.6.1 Observations from sensitivity studies ……… 140

6.6.2 Calibration charts……… 140

6.6.3 Other influencing factors……… 142

6.6.4 Limitations of calibration charts……… 143

6.6.5 Recommendations for finite element analysis… ……… 144

6.7 Application of 2-D finite element model to case studies……… 144

6.7.1 Case 1: MRT North East Line Singapore - Contract C704…… 145

6.7.2 Case 2: MRT Circle Line Stage 1 Singapore – Contract C825…… 147

6.7.3 Case 3: Centrifuge tests in stiff clay……… 149

6.8 Concluding remarks……… 149

CHAPTER 7 SUMMARY OF FINDINGS AND CONCLUSIONS 151

7.1 Introduction……… ……….……… 151

7.2 Field monitoring……… 151

7.3 3-D finite element simulation of tunnel advancement on adjacent pile foundation………… 154

7.4 Parametric studies……… 158

7.5 Plane strain idealisation of tunnel-pile interaction……… 160

7.6 Recommendations for future research……….……… 162

TABLES 164

FIGURES 177

REFERENCES 323

APPENDICES 333

NOTATIONS

The following nomenclature and symbols are adopted in this thesis

A G multiplier used in simple non-linear elastic soil model

At Slope of tangent modulus line

Apile Cross-sectional area of pile

Aeq Equivalent cross-sectional area of pile

Atun Cross-sectional area of tunnel

B Intercept of the tangent modulus line (also known as initial tangent modulus)

c’ Effective cohesion of soil

Cu Undrained shear strength of soil

Dwall(2D) Pile wall thickness in plane strain analysis

Dpile Pile diameter (=Dpile(3D))

Dtun Tunnel diameter

Ec Young’s modulus of concrete

Ecut Young’s modulus of over-cut element

Egrout.upp Young’s modulus of grout above tunnel springline

Egrout.bott Young’s modulus of grout below tunnel springline

Epile Young’s modulus of pile

Es Secant modulus of pile

Esoil Young’s modulus of soil

Eu Undrained Young’s modulus of soil

E’ Effective Young’s modulus of soil

Et Tangent modulus of pile

Eeq Equivalent Young’s modulus

E(wall)2D Pile stiffness in plane strain analysis

E(pile)3D Pile stiffness in 3-D analysis

EI Bending stiffness

EA Axial stiffness

EpileIpile Bending stiffness of pile

EpileApile Axial stiffness of pile

fb Limiting end bearing pressure

fs Limiting skin friction

G Shear modulus of soil

Gmax Maximum shear modulus of soil

Gmin Minimum shear modulus of soil

H Slope of Hvorslev surface in q, p’ surface in SDMCC model

Htun Tunnel depth (springline level) from ground surface

I Point of inflextion

Icracked Cracked moment of inertia of pile

Ipile Moment of inertia of pile

k Trough width parameter

k s Permeability of soil

K Bulk modulus of soil

Kmax Maximum bulk modulus of soil

Ko Earth pressure at-rest of soil

Lgrout Grout length to be in fluid state

Lp Pile length

Lp(debond) De-bonded pile length

M Critical state ratio

Mcr Cracked moment of pile

Mpile Pile bending moment

Mxx Pile bending moment in the transverse direction

Myy Pile bending moment in the longitudinal direction

Mult Ultimate bending moment capacity of pile

N Axial force in pile

n Strain exponent in simple non-linear elastic soil model

OCR Over-consolidation ratio of soil

Pgrout.upp Grout pressure above tunnel springline

Pgrout.bott Grout pressure below tunnel springline

Pgrout.uniform Uniform grout pressure

p’ Mean normal effective pressure of soil

p Contact pressure

q Deviatoric stress of soil

R Pile radius

s Surface settlement at a distance x from tunnel axis

S Slope of no-tension cut-off line in q,p’ space in SDMCC model

S1 Pile spacing in the transverse plane

S2 Pile spacing in the longitudinal plane

Smax Maximum surface settlement

teq Equivalent thickness

VL Volume loss caused by tunnelling

v Specific volume

Vo Initial volume of cavity (in pressuremeter test)

Xpile Distance between tunnel axis and centre of pile (for single pile) or centre of front

pile (for pile group)

XSB Clear distance between SB tunnel and the nearest pile

XNB Clear distance between NB tunnel and the nearest pile

x Distance from tunnel axis

X Transverse length of mesh

y Distance between strain gauges at equal distance and opposite direction from

neutral axis

Y Longitudinal length of mesh

z Distance from centroid to the extreme fibre of pile in tension

Z Vertical length of mesh

A, n1, m1, Experimental parameters to define shear modulus variation in SDMCC