Displacement of ground induced by surcharge loading and vacuum pressure

VIETNAM NATIONAL UNIVERSITY, HANOI VIETNAM JAPAN UNIVERSITY NGUYEN MINH DUC DISPLACEMENT OF GROUND INDUCED BY SURCHARGE LOADING AND VACUUM PRESSURE MASTER'S THESIS VIETNAM NATIONAL UNIVERSITY, HANOI VIETNAM JAPAN UNIVERSITY NGUYEN MINH DUC DISPLACEMENT OF GROUND INDUCED BY SURCHARGE LOADING AND VACUUM PRESSURE MAJOR: INFRASTRUCTURE ENGINEERING CODE: 8900201.04QTD RESEARCH SUPERVISOR: PROF NGUYEN DINH DUC DR NGUYEN TIEN DUNG Hanoi, 2021 ACKNOWLEDGEMENTS First of all, I would like to express my sincere thanks and appreciation to my supervisors, Prof Nguyen Dinh Duc and Dr Nguyen Tien Dung, who have guided me extensively to conduct this thesis for the part one year They spent a lot of time telling me complicated issues in geotechnical engineering They not taught me valuable knowledge about geotechnical engineering but also taught me valuable lessons about the seriousness and carefulness of scientific research These valuable lessons will follow me throughout the future studies I would like to sincerely thank other professors and lecturers at the Master program in Infrastructure Engineering (MIE) at Vietnam Japan University (VJU), who have taught me valuable knowledge in different fields of infrastructure engineering Especially, I would like to thank Dr Phan Le Binh of the MIE program, who has inspired and supported me a lot during my study at the University I would also to thank the assistants of the program, Mr Bui Hoang Tan and Mrs Bui Thi Hoa for their extensive support during my study period and thesis writing The thesis would haven‟t been completed without valuable monitored data from FECON Thus, I would like to take this chance to thank my colleagues at FECON, especially to Mr Do Xuan Hoang and other colleagues at FECON Infrastructure and Construction (FCIC) Company, who provided project data and supported me a lot I would also like to thank many colleagues at FECON, especially Dr Ngo Huy Dong, Mr Nguyen Tuan Anh (R&D Department), who have supported me significantly during my thesis preparation My sincere thanks are also to friends and engineers at FECON‟s geotechnical laboratory, where I had 30 meaningful days internship Finally, I would like to express my sincerely thanks to my parents and friends for their unflinching support in the tough time Their valuable support has driven me to complete this master thesis DECLARATION I declare that this thesis was composed by myself, that the work contained herein is my own except where explicitly stated otherwise in the text, and that this work has not been submitted for any other degree or professional qualification except as specified Nguyen Minh Duc TABLE OF CONTENTS LIST OF TABLES i LIST OF FIGURES ii LIST OF SYMBOLS iv ABSTRACT v Chapter INTRODUCTION 1.1 Problem statement 1.2 Necessity of the study 1.3 Objective and Scope of Research 1.3.1 Objectives of the Study 1.3.2 Scope of the Study 1.4 Structure of the thesis Chapter LITERATURE REVIEW 2.1 Prefabricated vertical drains used in ground improvement 2.1.1 History of PVD 2.1.2 PVD installation method statement 2.1.3 Smear effects 2.2 Vacuum consolidation used in ground improvement 2.2.1 Introduction of vacuum consolidation 2.3 Analytical solutions for settlement of improved grounds .9 2.3.1 Barron‟s theory on radial consolidation .9 2.3.2 Hansbo‟s solution for radial consolidation theory 11 2.3.3 Analytical model for vacuum preloading 12 2.3.4 Degree of consolidation (DOC) of vacuum preloading 14 2.3.5 Degree of consolidation (DOC) of combined preloading 15 2.3.6 Lateral displacements of ground 16 2.4 Numerical models for settlement of the improved grounds 18 2.4.1 Plane strain model with equivalent ground 18 2.4.2 Plane strain with drain elements .18 2.5 Simulation model in Plaxis 2D 20 2.5.1 Element types 20 2.5.2 Material models 21 Chapter METHODOLOGY 24 3.1 Applicability of the existing method 24 3.2 Establishment of the numerical procedure 25 3.3 Parametric studies 26 Chapter RESULTS AND DISCUSSIONS 28 4.1 Case histories .28 4.1.1 Case 1: Mizuki Park Project – Zone 28 4.1.2 Case 2: Long Thanh-Dau Giay Expressway Project 29 4.1.3 Case 3: Long Phu Project 31 4.1.4 Case 4: Tianjin Port Project .33 4.2 The applicability of the existing methods 35 4.3 Numerical procedure 40 4.4 Applicability of the numerical procedure 41 4.4.1 Mizuki park zone 41 4.4.2 Tianjin port .44 4.4.3 Long Thanh – Dau Giay Expressway 47 4.5 Results from parametric studies 50 4.5.1 Result of lateral displacement at the toe of embankment 51 4.5.2 Result of Influence zone 56 Chapter CONCLUSIONS AND RECOMMENDATIONS 61 5.1 Conclusion and recommendation 61 5.2 Limitation and Future works 62 REFERENCES 63 LIST OF TABLES Table 2.1 Characteristics of vertical drains .5 Table 2.2 Proposed smear zone parameters Table 2.3 Relationship to Cam-Clay parameters 23 Table 2.4 Relationship to internationaly normalised parameters 23 Table 4.1 The summary of the lateral displacement 38 Table 4.2 Assumed parameter model 42 Table 4.3 Assumed parameter model 45 Table 4.4 Assumed parameter model 47 Table 4.5 Parametric studies 50 Table 4.6 Material Parameter in Plaxis model 51 Table 4.7 The maximum lateral displacement values (δnm) at the toe of the embankment 54 Table 4.8 Influence zone .59 i LIST OF FIGURES Figure 1.1 Schematic illustration of ground improved by PVDs Figure 1.2 Schematic illustration of ground improved by vacuum and surcharge pressure Figure 1.3 Damages/failure in surrounding unimproved areas caused by vacuum preloading Figure 2.1 Installation of PVDs in the field (a) Flow chart of PVDs installation; (b) PVDs installation machine Figure 2.2 Membrane system Figure 2.3 Membraneless system Figure 2.4 Pore water pressure and effective stress changes Figure 2.5 Schematic soil cylinder with vertical drains 12 Figure 2.6 Vacuum pressure distribution in a unit cell 12 Figure 2.7 Pore water pressure distribution with depth, SCM load with VCM is applied .15 Figure 2.8 Lateral displacement induced by combination of SCM and VCM 16 Figure 2.9 Conversion from axisymmetric to a plane strain model 19 Figure 2.10 Problem type using 6-node and 15-node triangle elements .21 Figure 2.11 Relationship between volumetric strain and mean effective stress 22 Figure 2.12 Soft Soil model yield surface in q vs p‟ plane 23 Figure 3.1 The process to validate pplicability of the existing method 24 Figure 3.2 The process to establishment of numerical model .25 Figure 3.3 The process to establishment of parametric studies .26 Figure 4.1 Layout of Mizuki Park Project 27 Figure 4.2 Soil profile around the Mizuki Park Project 28 Figure 4.3 Map of Long Thanh - Dau Giay project 29 Figure 4.4 Soil profile at Long Thanh – Giay Day Project 30 Figure 4.5 Long Phu Project .31 Figure 4.6 The typical cross section of construction for plant area 32 Figure 4.7 Plan view of Tianjin port .33 Figure 4.8 Soil profile at Tianjin Port Project .34 Figure 4.9 Lateral displacement at Long Thanh – Dau Giay Project 35 Figure 4.10 Lateral displacement at Long Phu Project 36 Figure 4.11 Lateral displacement at Tianjin port 37 ii Figure 4.12 Comparision between monitoring and calculated value 38 Figure 4.13 Procedure to apply the vacuum modeling in Plaxis 2D .39 Figure 4.14 Mizuki park zone model 41 Figure 4.15 Compare of settlement between Plaxis model and observed data .42 Figure 4.16 Compare of lateral displacement between Plaxis model and observed data .43 Figure 4.17 Tianjin port model 43 Figure 4.18 Compare of settlement between Plaxis model and observed data .45 Figure 4.19 Compare of lateral displacement between Plaxis model and observed data .46 Figure 4.20 Long Thanh – Dau Giay Expressway model .46 Figure 4.21 Compare of settlement between Plaxis model and observed data .48 Figure 4.22 Compare of lateral displacement between Plaxis model and observed data .48 Figure 4.23 Simulation model of the improved ground 50 Figure 4.24 Lateral displacement values at the toe of the embankment for cases (1.1, 1.2, 1.3), cases (3.1, 3.2, 3.3), cases (5.1, 5.2, 5.3), cases (7.1, 7.2, 7.3) .51 Figure 4.25 Lateral displacement values at the toe of the embankment for cases (2.1, 2.2, 2.3), cases (4.1, 4.2, 4.3), cases (6.1, 6.2, 6.3), cases (8.1, 8.2, 8.3) 52 Figure 4.26 the relationship between the ratio Pv/Pt and maximum lateral displacement values (δnm) at the toe of the embankment with B = 20m 53 Figure 4.27 the relationship between the ratio Pv/Pt and maximum lateral displacement values (δnm) at the toe of the embankment with B = 30m 54 Figure 4.28 the relationship between the ratio Pv/Pt and maximum lateral displacement values (δnm) at the toe of the embankment with B = 40m 54 Figure 4.29 The relationship between the ratio Pv/Pt and maximum lateral displacement values (δnm) at the toe of the embankment with B = 20m, 30m, 40m 55 Figure 4.30 Infuence zone for cases (1.1, 1.2, 1.3), cases (3.1, 3.2, 3.3), cases (5.1, 5.2, 5.3), cases (7.1, 7.2, 7.3) .56 Figure 4.31 Infuence zone for cases (2.1, 2.2, 2.3), cases (4.1, 4.2, 4.3), cases (6.1, 6.2, 6.3), cases (8.1, 8.2, 8.3) .57 Figure 4.32 Influence zone case [Pv/Pt=0.68] : 58 Figure 4.33 Influence zone with B=30m .59 LIST OF SYMBOLS de k b diameter of influenced zone permeability VCM parameter representing the rate of restructuring horizontal coefficient of permeability for axis-symmetry in undisturbed zone coefficient of consolidation for vertical drainage horizontal coefficient of permeability for axis-symmetry in smear zone vacuum pressure method SCM surcharge loading method chi ch0 ck cs* e e0 Pt Ps coefficient of radial consolidation at effective pre-consolidation pressure initial coefficient of radial consolidation permeability index gradient of compression line in recompression region void ratio of soil initial void ratio soil Total loading; Pt=Ps + Pv surcharge loading vacuum pressure loading distance from the center of the drain radius of influenced zone radius of smear zone influence area kh cv ks Pv r re rs i iv 2.5 y = ax2 + bx + c - In this case: a = 13.289 b = -14.51 c= 4.668 I/B I/B 1.5 0.5 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 Pv/Pt Figure 4.33 Influence zone with B=30m In the Figure 4.30 and Figure 4.31, we can see that the influence zone will not change when changing the width of the embankment In the data Table 4.8 and Figure 4.33, we can see that the influence area will decrease when the value of the ratio Pv/Pt approaches 0.5 and the value of the affected area will increase when the ratio Pv/Pt moves away from 0.5 (increase or decrease compared to 0.5) The smallest influence zone value is reached when the Pv/Pt ratio is close to 0.5 60 CHAPTER CONCLUSIONS AND RECOMMENDATIONS 5.1 Conclusion and recommendation The primary objectives of this study are to establish a numerical procedure for estimating settlement and displacement of ground in and adjacent to the improved area and validate the applicability of the procedure The following are key conclusions drawn from the study 1) Reliability of analytical methods (chai et al 2013): The method of Chai et al (2013) gives similar values with monitored data However, this method only evaluates the maximum lateral displacement at the toe of the embankment 2) A numerical procedure using Plaxis 2D was proposed to determine settlement and displacements at different positions in and adjacent to the improved the ground The reliability of the procedure was validated through the good agreement of settlement and displacement obtained from the numerical procedure and from the measured data at three well-monitored projects 3) The validated numerical procedure was then applied to perform parametric studies on the lateral displacement of a typical PVD-improved ground under the combination of SCM and SVM with different loading ratio and embankment widths The behavior of lateral displacement and a number of correlations were developed and discussed: - The influence zone change insignificantly when changing the width of the embankment - The influence area will decrease when the value of the ratio Pv/Pt approaches 0.5 and the value of the affected area will increase when the ratio P v/Pt moves away from 0.5 (increase or decrease compared to 0.5) The smallest influence zone value is reached when the Pv/Pt ratio is close to 0.5 Such behavior and correlations and procedure (guideline) could sever as references for practicing engineers in analysis and design using this ground improvement meth 61 5.2 Limitation and Future works Limitation: The simulated physic-mechanical properties of the soft soil layer are almost the same as in reality However, within the limitations time of the study, there are no conditions to simulate many different types of geology, many different depths In addition, the solutions of construction techniques to reduce the lateral displacement near to the embankment have not been considered Suggestion: Continue to study the horizontal displacement of the soil when applying the VCM method for many different geological types, many different depths At the same time, study and develop other construction solutions to reduce lateral displacement next to the embankment such as using sheet pile walls etc 62 REFERENCES Asaoka, A (1978) Observation procedure of settlement prediction Soils and Foundations, pp 87-101 Barron, R A (1948) Consolidation of fine-grained soils by drain wells Transactions ASCE, pp 718-724 Bentley (2020) PLAXIS 2D V20-Reference Manual Bergado, D T., J C Chai, N Miura and A S Balasubramaniam (1998) PVD improvement of soft Bangkok clay with combined vacuum and reduced sand embankment preloading J Geotech Eng., Southeast Asian Geotch Soc., pp 95-122 Bergado, D T., J C Chai, N Miura and A S Balasubramaniam (1998) PVD improvement of soft Bangkok clay with combined vacuum and reduced sand embankment preloading J Geotech Eng., Southeast Asian Geotch Soc, pp 95-122 Bo, M W., J Chu, B K Low and V Choa (2003) Soil improvement; prefabricated vertical drain techniques Singapore: 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in the Figures below (a) Tension cut-off area I2 = 24m (b) Influence zone Figure A.1 Influence zone case [Pv/Pt=0.617] (a) Tension cut-off area; (b)Influence zone 67 (a) Tension cut-off area I3 = 19.5m (b) Influence zone Figure A.2 Influence zone case [Pv/Pt=0.553] (a) Tension cut-off area;(b) Influence zone 68 (a) Tension cut-off area I4 = 17m (b) Influence zone Figure A.3 Influence zone case [Pv/Pt=0.489] (a) Tension cut-off area; (b)Influence zone 69 (a) Tension cut-off area I5 = 27m (b) Influence zone Figure A.4 Influence zone case [Pv/Pt=0.425]; (a) Tension cut-off area; (b)Influence zone 70 (a) Tension cut-off area I6 = 41m (b) Influence zone Figure A.5 Influence zone case [Pv/Pt=0.361] (a) Tension cut-off area; (b) Influence zone 71 (a) Tension cut-off area I7 = 49m (b) Influence zone Figure A.6 Influence zone case [Pv/Pt=0.361] (a) Tension cut-off area; (b) Influence zone 72 (a) Tension cut-off area I7 = 49m (b) Influence zone Figure A.7 Influence zone case [Pv/Pt=0.297] (a) Tension cut-off area; (b)Influence zone 73 (a) Tension cut-off area I8 = 56m (b) Influence zone Figure A.8 Influence zone case [Pv/Pt=0.233] (a) Tension cut-off area; (b)Influence zone 74