Effect of a corner in a three dimensional excavation

EFFECT OF A CORNER IN A THREE-DIMENSIONAL EXCAVATION LOH CHANG KAAN (B.ENG. (HONS.) UTM, M.ENG. (NUS)) A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY DEPARTMENT OF CIVIL ENGINEERING NATIONAL UNIVERSITY OF SINGAPORE 2003 Dedicated to, my mother, wife, and two children for their ……… Continual support, encouragement, and Endless understanding Acknowledgements ACKNOWLEDGEMENTS Firstly, I would like to extend my deepest gratitude to my first supervisor, Associate Professor T. S. Tan for his concern and kindness, his continual effort on guiding, checking and providing ideas throughout my research work. Secondly, I would like to thank my second supervisor, Associate Professor F.H. Lee, who has provided me with some most critical ideas and approaches on handling daunting problems that emerged along the study. In addition, his encouragement is deeply appreciated. Both of my supervisors’ effort on initiating this research project and shaping up the framework of this study is acknowledged. One of the biggest problems on pursuing three-dimensional (3D) study is the handling of tremendous volume of data generated, compared to 2D study. It is very easy to be drawn into a whirlpool of data, lost the direction of study, and become exhausted along the way. It is my friend and colleague, Dr. J. Wang that helps me validate and prioritize the data, and assists to form a clearer focus of study. invaluable for the completion of this thesis. His support is Gratitude also extends to my senior and friend, Dr. T.G. Ng, for his critical proofreading of the thesis, often late into the night. I would also like to thanks all the laboratory technologists in the Geotechnical Laboratory, especially Mr. C.Y. Wong, for their help in the experimental works. Acknowledgement also extends to all my fellow research engineers and scholars for sharing their experience and stimulating discussion. i Table of Contents TABLE OF CONTENTS Page Title Page Acknowledgements i Table Of Contents ii List Of Figures vi List Of Tables xv Summary xvi Nomenclature xix CHAPTER INTRODUCTION 1.1 Three Dimensional Behaviour Of Deep Excavation 1.2 Current Understanding On 3D Behaviour Of Deep Excavation 1.3 Approach To A Better Understanding On Corner Effect In Deep Excavation 1.4 Necessities Of Centrifuge Model Test 1.5 Objectives Of The Study CHAPTER LITERATURE REVIEW 2.1 Introduction 8 2.2 Literature Review On Centrifuge Modelling On Deep Excavation 11 2.2.1 Various Methods To Model Excavation In Centrifuge 12 2.2.1.1 Increasing-g Method 12 2.1.1.2 Excavate and Spin Method 13 2.2.1.3 Heavy Liquid Method 13 2.2.1.4 2D In-Flight Excavation Test In The Centrifuge 15 2.2.1.5 Tunnel Excavation Method 17 2.2.2 The Challenge Of 3D In-Flight Excavation Test 2.3 Literature Review On 3D Excavation Behaviour 2.3.1 General Appreciation Of 3D Excavation Behaviour 18 19 19 ii Table of Contents 2.3.2 Quantification Of 3D Corner Effect 22 2.3.3 Influence Range Of 3D Corner Effect 25 2.3.4 Other Parameters Which Might Influence Corner Effect 29 2.4 Summary CHAPTER DEVELOPMENT OF 3D IN-FLIGHT EXCAVATOR AND 30 32 CENTRIFUGE MODEL TESTS 3.1 Design And Development Of 3D In-Flight Excavator 32 3.2 Experimental Details 35 3.2.1 The Model Retaining Wall 35 3.2.2 Soil Sample Preparation 37 3.2.3 Centrifuge Model Container Preparation 40 3.2.4 Instrumentation And Excavator Set-Up 41 3.2.5 Excavation Procedures 43 3.3 The Conditions Of In-Flight Excavation Tests 44 3.3.1 Area Modelled In The Experiments 44 3.3.2 Fixities And Water Table Boundary Conditions 45 3.4 Methodology Of Test 46 3.4.1 Parametric Study On The Effect Of Wall Stiffness 46 3.4.2 Parametric Study On The Effect Of Capping Beam 46 3.4.3 Parametric Study On Influence Of Geotechnical Effect To 47 3D Corner Effect CHAPTER EXPERIMENTAL RESULTS AND DISCUSSIONS 4.1 Introduction 48 48 4.1.1 Initial Conditions Of Tests 48 4.1.2 Soil Characterization 49 4.1.3 Prototype Modelled and Other Consideration 51 4.2 General Characteristics Of 3D Excavation Behaviour 4.2.1 Characteristics Of Surface Settlement And Wall Deflection 52 53 iii Table of Contents 4.2.2 Characteristics Of Lateral Earth Pressure On Retaining Wall 59 4.3 2D Versus 3D Excavation Behaviour 62 4.4 Retaining Wall Thickness Effect In A Corner Excavation 67 4.5 Presence Of A Capping Beam In A 3D Excavation 70 4.6 Effect Of Soil Strength In 3D Excavation 72 4.7 Summary 74 CHAPTER FUNDAMENTAL BEHAVIOUR OF CORNER EFFECT 76 IN EXCAVATION 5.1 Introduction 76 5.2 Finite Element Analysis 77 5.2.1 Parametric Studies By Varying Excavation Dimensions Of A 80 Corner Excavation 5.2.2 Parametric Studies On The Effect Of Wall Stiffness And The 84 Presence Of Capping Beam To 3D Corner Effect 5.2.3 Summary Of Findings From FEM Studies 5.3 Characterisation Of Corner Effects 85 86 5.3.1 Major Factors Affecting The Corner Effect 86 5.3.2 Characterization Of Structural Factor 88 5.3.2.1 Deformation Due To Excavation Induced Imbalance 88 Load 5.3.2.2 The Effect Of Structural Restraint At Corner 92 5.3.2.3 Corner Effect Due To Structural Restrain At Corner 94 5.3.2.4 The Corner Effect Influence Range 96 5.3.3 Characterization Of Geotechnical Factors 101 5.4 Combined Characterization Of Corner Effect 5.4.1 Evaluation Of Corner Effect Hypotheses CHAPTER CONCLUSIONS 106 107 113 6.1 Development Of 3D In-Flight Excavator 113 6.2 Summary Of Findings 114 iv Table of Contents 6.3 Effect Of A Corner In A 3D Excavation 115 6.4 Recommendation For Future Studies 117 TABLES 120 FIGURES 127 REFERENCES 222 v List of Figures LIST OF FIGURES Figure No. Fig. 1.1 Description A schematic diagram showing a typical excavation carried out in the field Page 127 Fig. 2.1 Observed settlements behind strutted excavation in Chicago (after O’ Rourke et al., 1976) 128 Fig. 2.2 Observed settlements behind excavation (after Peck, 1969) 128 Fig. 2.3 Relationship between factor of safety against basal heave and maximum lateral wall movement from case histories (after Clough et al., 1979) 129 Fig. 2.4 Relationship between maximum ground settlements and maximum lateral wall movement from case histories (after Mana & Clough, 1981) 129 Fig. 2.5 Apparent pressure diagrams for computing strut loads in braced cuts (after Terzaghi et al. 1996) 130 Fig. 2.6 Distress caused to a buried service by a shallow trenching operation (after Needham and Howe, 1984) 131 Fig. 2.7 Schematic representation of the “Increasing-g” method to simulate excavation 132 Fig. 2.8 Schematic representation of the “Heavy Liquid” method to simulate excavation 132 Fig. 2.9 TIT’s in-flight excavator setup (after Kimura et al. 1994) 133 Fig. 2.10 a) Vertical cut with corner angle ∝ (after Giger and Krizek, 1975) b) Stability factor Ns as a function of the corner angle ∝ (after Giger and Krizek, 1975) 134 Fig. 2.11 Stability Number versus Depth of Excavation Divided by Radius (after Britto and Kusakabe, 1983) 135 Fig. 2.12 2D Section Used in Trench Excavation Analysis (after De Moor, 1994) 136 Fig. 2.13 PSR Chart (After Ou et al. 1996) 137 Fig. 2.14 Typical Analysis on a 10m long x 6m deep x 1m wide trench excavation. Ground movement along line e – e 138 vi List of Figures parallel to trench and located 2m below surface: Comparison between results from three-dimensional and plane strain analyses (after Nath, 1983) Fig. 2.15 Variation of maximum wall displacement with the distance from for constant sizes of complementary wall and various sizes of primary wall, L = Length of primary wall; B = length of complementary wall. After Ou et al. (1996) 139 Fig. 3.1 3D in-flight excavator set-up on centrifuge 140 Fig. 3.2 Schematic diagrams of the 3D in-flight excavator 141 Fig. 3.3 Schematic representation of 3D in-flight excavator setup on the centrifuge during testing 142 Fig. 3.4 Indexers/drivers mounted on-board the centrifuge 143 Fig. 3.5 Internal parts of indexers/drivers strengthened by silicone sealant. The indexers/drivers was mounted near to the centrifuge rotating shaft to minimized centrifugal force during spinning. 143 Fig. 3.6 Schematic drawing of a corner of an excavation simulated 144 Fig. 3.7 2D in-flight excavation test set-up on a narrow centrifuge container 145 Fig. 3.8 Micro-concrete wall used in the study 146 Fig. 3.9 One of the aluminum alloy wall used in the study. 146 Fig. 3.10 Plan view of the excavation set-up & LVDT set-out for Test 3DK-2 147 Fig. 3.11 Locations of SGs and TSTs in the experiment: Test 3DK-2c 147 Fig. 3.12 Schematic representation of OCR profiles intended 148 Fig. 3.13 De-airing of pore pressure transducers by boiling 149 Fig. 3.14 Installation of pore pressure transducers into soil sample 149 Fig. 3.15 a) Completed 3D in-flight excavation test set-up before transporting to centrifuge room b) 3D in-flight excavation test set-up after 150 vii List of Figures excavation test on centrifuge platform Fig. 3.16 Excavation in Progress (captured by miniature camera mounted in front of the test sample) 151 Fig. 4.1 Surface settlement versus elapsed reconsolidation time (Test 3DK-3) 152 Fig. 4.2 Hyperbolic plot, Elapsed time/Settlement versus Elapsed Time (Test 3DK-3) 152 Fig. 4.3 Density and undrained shear strength profiles of NC soil used in the experiments 153 Fig. 4.4 Schematic plan view of model retaining wall edge at container wall face 154 Fig. 4.5 Responses of LVDTs installed at difference planes (Test 3DK-2) 155 Fig. 4.6 Flow chart showing centrifuge tests conducted 156 Fig. 4.7 Locations of LVDTs, SG and TST in the experiment: Test 3DK-2c 157 Fig. 4.8 Test: 3DK-2c: Surface settlement at various location behind the retaining wall 158 Fig. 4.9 Surface settlement profiles behind wall, at various section from corner 159 Fig. 4.10 Surface settlement behind wall: Test 3DK-2c compare 2D tests and published data (after Peck 1969) S = Surface settlement h = Depth of excavation D = Distance behind wall 160 Fig. 4.11 Surface settlement profiles at various distances from corner: at 3.0m and 7.0m behind wall (Test 3DK-2c) 161 Fig. 4.12 Surface settlement contour behind retaining wall (Test 3DK-2c) 162 Fig. 4.13 Wall deflection profiles at Perspex window (Test 3DK-2c) 163 Fig. 4.14 A typical scraping of layer of soil in 3D in-flight excavation test 163 Fig. 4.15 Incremental surface settlement of a single scrapping 164 viii 0.14 1m exc 2m exc 3m exc 4m exc 5m exc 6m exc 7m exc a) Offset-Sett (m) 0.12 0.10 0.08 0.06 0.04 0.02 0.00 10 15 x, distance from corner (m) 20 10 x, distance from corner (m) 15 20 10 x, distance from corner (m) 15 20 0.20 b) Offset-Sett /λs (m) 0.16 0.12 0.08 0.04 0.00 c) Offset-Sett /(λs *λa) (m) 0.20 0.16 0.12 0.08 0.04 0.00 Fig. 5.37 Offset-surface settlement at 7m behind wall versus x: Test 3DK-1 a) Offset-Sett before normalization b) Offset-Sett normalized with λs c) Offset-Sett normalized with λa and λs 217 a) Offset-Sett (m) 0.12 1m exc 2m exc 3m exc 4m exc 5m exc 6m exc 7m exc 0.08 0.04 0.00 10 15 x, distance from corner (m) 20 0.20 b) Offset-Sett /λs (m) 0.16 0.12 0.08 0.04 0.00 10 x, distance from corner (m) 15 20 10 x, distance from corner (m) 15 20 c) Offset-Sett /(λs *λa) (m) 0.24 0.20 0.16 0.12 0.08 0.04 0.00 Fig. 5.38 Offset-surface settlement at 7m behind wall versus x: Test 3DK-2 a) Offset-Sett before normalization b) Offset-Sett normalized with λs c) Offset-Sett normalized with λa and λs 218 a) Offset-Sett (m) 0.06 1m exc 2m exc 3m exc 4m exc 5m exc 6m exc 7m exc 0.04 0.02 0.00 10 15 x, distance from corner (m) 20 10 x, distance from corner (m) 15 20 10 x, distance from corner (m) 15 20 0.20 b) Offset-Sett /λs (m) 0.16 0.12 0.08 0.04 0.00 c) Offset-Sett /(λs *λa) (m) 0.20 0.16 0.12 0.08 0.04 0.00 Fig. 5.39 Offset-surface settlement at 7m behind wall versus x: Test 3DK-3 a) Offset-Sett before normalization b) Offset-Sett normalized with λs c) Offset-Sett normalized with λa and λs 219 2DK-1 2DK-3 3DK-1: x=4.2 3DK-1: x=9.8 3DK-1: x=15.2 3DK-2: x=4.2 3DK-2: x=9.8 3DK-2: x=15.2 3DK-3: x=9.8 1.0 a) δ (m) 0.8 0.6 0.4 0.2 0.0 h, depth of excavation (m) 1.0 b) δ/λs (m) 0.8 0.6 0.4 0.2 0.0 h, depth of excavation (m) 1.0 c) δ/(λs *λa) (m) 0.8 0.6 0.4 0.2 0.0 h, depth of excavation (m) Fig. 5.40 Wall top displacement versus depth of excavation: Tests 3DK-1, 3DK-2 and 3DK-3 a) δ before normalization b) δ normalized with λs 220 c) δ normalized with λa and λs a) Offset-sett (m) 0.60 2DK-3 3DK-1: x=3.5 3DK-1: x=9.1 3DK-1: x=14.5 3DK-2: x=3.5 3DK-2: x=9.1 3DK-2: x=14.5 3DK-3: x=3.5 3DK-3: x=9.1 3DK-3: x=14.5 0.50 0.40 0.30 0.20 0.10 0.00 h, depth of excavation (m) 0.60 b) Offset-sett /λs (m) 0.50 0.40 0.30 0.20 0.10 0.00 h, depth of excavation (m) c) Offset-sett /(λs *λa) (m) 0.60 0.50 0.40 0.30 0.20 0.10 0.00 h, depth of excavation (m) Fig. 5.41 Offset-settlement versus depth of excavation: Tests 3DK-1, 3DK-2 and 3DK-3 a) Offset-Sett before normalization b) Offset-Sett normalized with λs 221 c) Offset-Sett normalized with λa and λs References 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Centrifuge 94, Singapore: 643 – 647. 1994. 232 [...]... such as excavation for pipe laying and drainage works In a cofferdam excavation, such as basement excavation where excavation size is limited, there are inevitable interactions between adjacent planes with distance from corner For sections near the mid-span of a large excavation, the behaviour may be approaching that of a 2D problem However, the influence range and under what conditions this is valid... stiffness of the retaining wall plays an important role in the behaviour of an excavation By varying the characteristics of the retaining wall, such as the wall stiffness, such effects on the overall behaviour of an excavation can be carefully evaluated iii) Effects of soil properties 4 Chapter 1 Introduction The effects of soil properties in an excavation can also be assessed through parametric studies... are able to explain major aspects of 3D corner effects in the excavations xviii Nomenclature NOMENCLATURE A cross sectional area of the retaining wall B the width of excavation D distance behind retaining wall E the Young’s modulus of the wall g gravitational force I second moment of area L the length of excavation Lm length from corner when lateral flexural capacity is exceeded Ll simplified corner effect. .. and to model realistic excavation sequences The development of an in- flight excavation apparatus suitable for 3D excavation is already a very complicated task To put in place an in- flight strutting system is more daunting and was not pursued in this project Thus in this study, unstrutted excavation was carried out In all excavations, the first stage is usually an unstrutted excavation If the excavation. .. APPROACH TO A BETTER UNDERSTANDING ON CORNER EFFECT IN DEEP EXCAVATION Currently, there are a number of numerical programs capable of performing 2D and 3D excavation analyses, such as CRISP, FLAC, ABAQUS, PLAXIS and DIGDIRT 2 Chapter 1 Introduction These programs are able to model the soil-structural interaction in a realistic sequence of operation that follows closely the actual geometry of excavation. .. the salient feature of corner effects This includes the establishment on how the 3D effect is developed, the contributors of such effects and the influence to an excavation In many of these excavations, capping beams are provided These are seldom evaluated, mainly because in 2D analyses, such an effect cannot be accounted for The capping beam effect in an excavation is assessed in this study 7 Chapter... λs corner effect factor due to corner structural restrain a corner effect factor due to geotechnical effect γ the total unit weight of soil a the Rankine active earth pressures σp the Rankine passive earth pressures γh cu xx Chapter 1 Introduction CHAPTER 1 INTRODUCTION 1.1 THREE DIMENSIONAL BEHAVIOUR OF DEEP EXCAVATION Excavation of soil as part of a major infrastructure construction is a common activity... BEHAVIOUR OF DEEP EXCAVATION For an excavation supported by retaining wall, the unbalance load due to the removal of earth would cause movement to occur wall and the associated bracing system This movement is restrained by the retaining This is a classical soil-structure interaction problem, and many 2D solutions are available In engineering practice, it is intuitively recognized that the presence of. .. effect, such as corner of a retaining wall, would influence the soil-structural interaction predicted by the 2D analysis For example, it is generally accepted that the corner of a cofferdam is stiffer than other section far from corner It is also generally recognized that the movement of a small size excavation would be smaller than that of larger excavation In trenching works, engineers would usually... soil parameters used for FEM analyses 124 Table 5.2 Initial stress conditions of FEM analyses 125 Table 5.3 Summary of findings from centrifuge modelling and FEM analyses 126 xv Summary SUMMARY In reality, all excavations are three- dimensional (3D) in nature In routine engineering practices, the complicated 3D problem is often simplified and idealised into much simpler plane strain two -dimensional (2D) . Retaining Wall Thickness Effect In A Corner Excavation 67 4.5 Presence Of A Capping Beam In A 3D Excavation 70 4.6 Effect Of Soil Strength In 3D Excavation 72 4.7 Summary 74 CHAPTER 5 FUNDAMENTAL. Summary of findings from centrifuge modelling and FEM analyses 126 xv Summary SUMMARY In reality, all excavations are three- dimensional (3D) in nature. In routine engineering practices,. FUNDAMENTAL BEHAVIOUR OF CORNER EFFECT IN EXCAVATION 76 5.1 Introduction 76 5.2 Finite Element Analysis 77 5.2.1 Parametric Studies By Varying Excavation Dimensions Of A Corner Excavation 80