Advanced Finite Element Analysis of Deep Excavation Case Histories

247 Pages·2014·9.48 MB·English

DEPARTMENT OF ENGINEERING SCIENCE
UNIVERSITY OF OXFORD

Advanced Finite Element Analysis of
Deep Excavation Case Histories
Yuepeng Dong

A thesis submitted for the degree of Doctor of Philosophy at
University of Oxford

Christ Church
Hilary Term 2014
Declaration

I declare that, except where specific reference is made to the works of others, the contents of this
thesis are original and have never been submitted, in part or as a whole, to any other university
for any degree, diploma or other qualifications.
This thesis is the result of my own work and includes nothing which is the outcome of work
done in collaboration.

Yuepeng Dong
December 2013

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Acknowledgements
There are a number of people I need to acknowledge here during my study at Oxford.
Firstly, I would like to thank my supervisors, Dr Harvey J. Burd and Professor Guy T. Houlsby,
for their generous time of regular meetings and valuable advices during discussions. Guy
encouraged me to apply for Oxford and provided guidance in the application, while Harvey is
the leading supervisor for my research. I am fortunate to have them both as my supervisors, and
this experience will stay in my memory forever. The examiners, Prof. David Potts and Prof.
Tony Blakeborough, commented on this thesis and gave corrections during and after the viva.
Secondly, it is my alma mater, Shanghai Jiao Tong University, where I started learning Civil
Engineering, built up my friendship, developed my leadership, and enhanced my skills in
research. My experiences and skills in Shanghai are essential for my research in Oxford, and also
critical to help me secure a postdoctoral position working with Prof. Andrew J. Whittle at MIT.
My whole study in Oxford is sponsored by a scholarship from China Scholarship Council, and
the application was made in Shanghai. The case histories in the thesis are provided by Dr
Zhonghua Xu, a PhD graduate from Shanghai Jiao Tong University, who did the field
measurement and analysed the field data in his PhD thesis.
Thirdly, many thanks also go to my colleagues and friends in the university and colleges. With
them, I never feel lonely in Oxford. The daily communication with my fellow students in the
department is entertaining and enlightening. The experience in OUSU is enjoyable, first in the
Environment & Ethics Committee, and then serving as the MPLS Divisional Graduate
Representative. The social life in my college, Christ Church, is amazing and unforgettable, both
involving in the governing committee of Christ Church GCR as OUSU Representative and Bar
Representative, and also rowing in the prestigious Christ Church Rowing Club.
Last but not least, I wish to thank my parents and sister who encouraged my study abroad and
never made me worry about them in China.
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Abstract
Deep excavations have been used worldwide for underground construction, but they also alter
the ground conditions and induce ground movements which might cause risks to adjacent
infrastructure. Field measurements are normally carried out during excavations to ensure their
safety, and also provide valuable data to calibrate the results from the numerical analysis which
is an effective way to investigate the performance of deep excavations. This thesis is concerned
with evaluating the capability of advanced finite element analysis in reproducing various aspects
of observed deep excavation behaviour in the field through back analysis of case histories. The
finite element model developed considers both geotechnical and structural aspects such as (i)
detailed geometry of the excavation and retaining structures, (ii) realistic material models for the
soil, structures and the soil-structure interface, and (iii) correct construction sequences.
Parametric studies are conducted first based on a simplified square excavation to understand the
effect of several important aspects, e.g. (i) the merit of shell or solid elements to model the
retaining wall, (ii) the effect of construction joints in the retaining wall, (iii) the effect of the
operational stiffness of concrete structural components due to cracks, (iv) the thermal effect of
concrete beams and floor slabs during curing process and due to variation of ambient
temperature, (v) the effect of soil-structure interface behaviour, and (vi) the effect of stiffness
and strength properties of the soil. Two more complex case histories are then investigated
through fully 3D analyses to explore the influence of various factors such as (i) neglecting the
small-strain stiffness nonlinearity in the soil model, (ii) the selected value to represent the
initial stress state in the ground, (iii) the appropriate anisotropic wall properties to consider the
joints in the diaphragm wall, (iv) the parameters governing the settlements of adjacent buildings
and buried pipelines, (v) the effectiveness of ground improvement on reducing the building
settlement, (vi) the variation of construction sequences, (vii) the effectiveness of earth berms,
and (viii) ignoring the openings in the floor slabs. This research has strong practical implications,
but cautions should also be taken in applications, e.g. element types and parameter selection.
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Table of Contents
Declaration ..................................................................................................................................... 2
Acknowledgements ........................................................................................................................ 3
Abstract .......................................................................................................................................... 4
Table of Contents .......................................................................................................................... 5
Chapter 1 Introduction ............................................................................................................... 10
1.1 Background .......................................................................................................................... 10
1.2 Limitations in previous and current research ...................................................................... 12
1.3 Advantages of advanced numerical analysis ....................................................................... 14
1.4 Objectives and practical implications of this research ........................................................ 14
1.5 Structure of the thesis .......................................................................................................... 15
Chapter 2 Literature review on deep excavations.................................................................... 18
2.1 Introduction ......................................................................................................................... 18
2.2 Theoretical and empirical methods...................................................................................... 18
2.2.1 Classical earth pressure theory ...................................................................................... 18
2.2.2 Stability analysis ........................................................................................................... 19
2.2.3 Stress path method ........................................................................................................ 20
2.2.4 Empirical methods ........................................................................................................ 21
2.3 Laboratory tests and field measurements ............................................................................ 24
2.3.1 Wall deformation .......................................................................................................... 25
2.3.2 Ground movement ........................................................................................................ 27
2.3.3 Earth and pore water pressure ....................................................................................... 29
2.3.4 Prop loads and wall bending moments ......................................................................... 31
2.3.5 Deformation and damage of adjacent infrastructure ..................................................... 32
2.4 Numerical modelling ........................................................................................................... 37
2.4.1 Model details and simulation process ........................................................................... 37
2.4.2 Constitutive models for the soil, structures, and the soil/structure interface ................ 43
2.4.3 Results obtained and lessons learnt ............................................................................... 48
2.5 Summary .............................................................................................................................. 52
Chapter 3 Advanced finite element analysis of deep excavations ........................................... 54
3.1 Introduction ......................................................................................................................... 54
3.2 Components in braced deep excavations ............................................................................. 54
3.2.1 The soil .......................................................................................................................... 54
3.2.2 The retaining wall ......................................................................................................... 55
3.2.3 The support system ....................................................................................................... 57
3.2.4 Adjacent infrastructure .................................................................................................. 57
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3.2.5 Constraints and contacts ............................................................................................... 57
3.2.6 Boundary conditions ..................................................................................................... 58
3.3 Material models ................................................................................................................... 58
3.3.1 Constitutive models for the soil .................................................................................... 58
3.3.2 Constitutive models for structural components ............................................................ 69
3.3.3 Constitutive models for the soil-structure interface ...................................................... 71
3.4 Modelling procedures .......................................................................................................... 73
3.4.1 Geostatic analysis .......................................................................................................... 73
3.4.2 Wall and pile installation .............................................................................................. 74
3.4.3 Soil removal and structure installation ......................................................................... 74
3.4.4 Dewatering and consolidation ....................................................................................... 75
3.5 Summary .............................................................................................................................. 75
Chapter 4 Parametric studies of an idealised square excavation ........................................... 76
4.1 Idealised square excavation ................................................................................................. 76
4.1.1 Geometry of the excavation .......................................................................................... 76
4.1.2 Construction sequence .................................................................................................. 77
4.1.3 Finite element model ..................................................................................................... 78
4.1.4 Material models and input parameters .......................................................................... 80
4.2 Strategy of the analyses ....................................................................................................... 80
4.3 Influence of element types ................................................................................................... 81
4.3.1 Modelling the soil and structures: linear or quadratic elements ................................... 81
4.3.2 Modelling the retaining wall: solid or shell elements ................................................... 83
4.3.3 Modelling the piles: solid or beam elements ................................................................ 85
4.4 Influence of the operational stiffness of retaining structures .............................................. 86
4.4.1 Influence of the operational stiffness of the diaphragm wall ........................................ 86
4.4.2 Influence of the stiffness of horizontal beams and floor slabs ...................................... 89
4.4.3 Influence of the stiffness of vertical piles ..................................................................... 90
4.4.4 Influence of the stiffness of the wall, floor slabs and piles ........................................... 91
4.5 Influence of thermal effects of concrete structures ............................................................. 92
4.6 Influence of soil-structure contact and interface properties ................................................ 94
4.6.1 Mechanisms of contact between the soil and structures ............................................... 95
4.6.2 Influence of the soil/wall interface properties .............................................................. 96
4.6.3 Influence of the soil/pile interface properties ............................................................... 97
4.6.4 Influence of the soil/wall and soil/pile interface properties .......................................... 99
4.7 Influence of the discontinuity in the retaining wall ........................................................... 101
4.8 Influence of stiffness and strength parameters of the soil ................................................. 103
4.9 Improved analyses ............................................................................................................. 105
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4.10 Conclusions ..................................................................................................................... 108
Chapter 5 Basement excavation for Shanghai Xingye Bank building ................................. 114
5.1 Introduction ....................................................................................................................... 114
5.2 Project description ............................................................................................................. 115
5.2.1 General description ..................................................................................................... 115
5.2.2 Geotechnical conditions and soil properties ............................................................... 116
5.2.3 The retaining system ................................................................................................... 117
5.2.4 Construction sequences ............................................................................................... 120
5.2.5 Instrumentations .......................................................................................................... 120
5.3 Finite element model and strategy of the analyses ............................................................ 122
5.3.1 Finite element model description ................................................................................ 122
5.3.1 Strategy of analyses .................................................................................................... 125
5.4 Interpretation of results ...................................................................................................... 131
5.4.1 Central analysis ........................................................................................................... 133
5.4.2 Influence of thermal effects of concrete ..................................................................... 138
5.4.3 Influence of joints in the diaphragm wall ................................................................... 140
5.4.4 Effect of shell and solid element for the wall ............................................................. 143
5.4.5 Influence of the initial stress state in the ground ........................................................ 146
5.4.6 Influence of soil models .............................................................................................. 149
5.5 Conclusions ....................................................................................................................... 152
Chapter 6 Deformation of adjacent infrastructure induced by deep excavations .............. 156
6.1 Introduction ....................................................................................................................... 156
6.2 Information on adjacent infrastructure .............................................................................. 157
6.2.1 Information on buildings ............................................................................................. 158
6.2.2 Ground improvement .................................................................................................. 162
6.2.3 Buried Pipelines .......................................................................................................... 162
6.3 Description of the finite element model ............................................................................ 164
6.3.1 Mesh of the buildings .................................................................................................. 165
6.3.2 Foundations of the buildings ....................................................................................... 165
6.3.3 Ground improvement .................................................................................................. 166
6.3.4 The buried pipelines .................................................................................................... 167
6.4 Strategies of the analyses ................................................................................................... 168
6.5 Interpretation of the results ................................................................................................ 169
6.5.1 Central analysis ........................................................................................................... 169
6.5.2 Influence of the building stiffness ............................................................................... 174
6.5.3 Influence of the building weight ................................................................................. 176
6.5.4 Influence of the stiffness of the foundation ................................................................ 177
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6.5.5 Influence of ground improvement .............................................................................. 178
6.5.6 The settlement of the pipelines ................................................................................... 181
6.6 Conclusions ....................................................................................................................... 183
Chapter 7 Deep excavation for the North Square of Shanghai South Railway Station ..... 186
7.1 Introduction ....................................................................................................................... 186
7.2 Project description ............................................................................................................. 187
7.2.1 General description ..................................................................................................... 187
7.2.2 Geotechnical conditions and soil properties ............................................................... 189
7.2.3 The Retaining system .................................................................................................. 190
7.2.4 Construction procedures ............................................................................................. 192
7.2.5 Instrumentation ........................................................................................................... 193
7.3 FEM model description and input parameters ................................................................... 194
7.3.1 FEM model description ............................................................................................... 194
7.3.2 Input material properties ............................................................................................. 197
7.4 Strategy of Analyses .......................................................................................................... 199
7.5 Interpretation of results ...................................................................................................... 202
7.5.1 Central analysis ........................................................................................................... 202
7.5.2 Influence of the unzoned excavation .......................................................................... 207
7.5.3 Influence of construction sequences ........................................................................... 208
7.5.4 Influence of the earth berms ....................................................................................... 210
7.5.5 Influence of opening access ........................................................................................ 212
7.6 Conclusions ....................................................................................................................... 214
Chapter 8 Conclusions and recommendations ....................................................................... 216
8.1 Conclusions ....................................................................................................................... 216
8.2 Limitations in the analyses and recommendations for future work ................................... 221
References .................................................................................................................................. 225
Appendix A - Field data of basement excavation for Shanghai Xingye Bank building ..... 235
A.1 Lateral displacement of the diaphragm wall ................................................................. 235
A.2 Vertical movement of the diaphragm wall ................................................................... 236
A.3 Lateral displacement of the ground .............................................................................. 236
A.4 Ground settlement and adjacent wall deflection ........................................................... 237
A.5 Pipeline settlement ........................................................................................................ 238
A.6 Building deformation .................................................................................................... 240
Appendix B - Field data of excavation for North Square of Shanghai South Railway Station
..................................................................................................................................................... 243
B.1 Lateral displacement of the diaphragm wall ................................................................. 243
B.2 Vertical displacement of diaphragm wall ..................................................................... 247
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B.3 Vertical displacement of piles and horizontal support system ..................................... 247

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Chapter 1 Introduction
Chapter 1 Introduction
1.1 Background
Deep excavations are widely used in urban areas for the development of underground space, e.g.
subway stations, basements for high-rise buildings, underground car parks and shopping centres.
However, the excavation process inevitably alters the stress states in the ground and may cause
significant wall deformations and ground movements. Especially when the excavation is close to
adjacent infrastructure, e.g. buildings, tunnels, buried pipelines, piled foundations, the excavation
induced ground movements must be carefully monitored and controlled within an acceptable
amount, to avoid any potential damage to these classes of infrastructure. The failure of an
excavation may have catastrophic consequences, and special care must be taken to avoid such
failure. One disaster of this sort is the collapse of a deep excavation adjacent to Nicoll Highway
in Singapore on 20 April 2004 (Fig.1.1), resulting in four casualties and a delay of part of the
Circle Line subway project.

Fig.1.1 Singapore Nicoll Highway collapse adjacent to an excavation
The main causes of failure are various, e.g. unexpected soil conditions, rupture of the anchoring
or bracing system (e.g. buckling or inadequate connection to the wall), violating the designed
construction sequences (e.g. overexcavation). In most cases, however, the pre-failure
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