Consolidation Analysis of PVD-Installed Soft Deposits Considering Soil Disturbance and Discharge Capacity Reduction
- Abstract
- Prefabricated vertical drains (PVDs) combined with preloading are frequently used to accelerate rate of consolidation and gain shear strength in soft soils. PVD discharge capacity reduction and soil disturbance caused by PVD installation are important factors in ground improvement design, these factors significantly affect the consolidation behavior of PVD-improved ground. In this thesis, a numerical solution for radial consolidation of PVD-installed deposits, formulates a general expression for discharge capacity reduction with consolidation process, is proposed based on large-strain theory. The effects of soil disturbance, such as a nonlinear distribution for radial hydraulic conductivity, are captured. The proposed solution was applied to a test embankment at Saga Airport and an experimental test. The predicted results of consolidation behaviors were in good agreement with observed data in all cases of the verification.
In order to perform a multi-drain analysis in numerical model, equivalent plane strain models were proposed. An equivalent vertical hydraulic conductivity ( method) is proposed to consider the effects of PVD discharge capacity reduction with increased confining pressure. The proposed method was validated via a test embankment on a thick soft ground for construction site in Busan New Port. The results indicated that it is necessary to consider the PVD discharge capacity reduction with depth on consolidation analysis. A nonlinear distribution of discharge capacity with depth is recommended to use in practice.
To realistically simulate existence of PVD in soft ground, an equivalent plane strain model using solid element was further proposed. In the proposed method, an equivalent horizontal permeability was obtained from the matching of the total volume of water to be discharged in an axisymmetric model and the total changes in flow in a plane strain, while the geometry of the drains was deduced from the balancing of the area ratio. The effects of the soil disturbance and well resistance were also considered. The verification was implemented; and the predicted results by the proposed method were in good agreement with observed data for two case histories, including the test embankment on the soft clay of eastern China and the Malaysian soft muar clay. It is recommended that the proposed models could be used for consolidation analysis of the PVD-installed soft deposits.
- Issued Date
- 2019
- Awarded Date
- 2019. 2
- Type
- Dissertation
- Publisher
- 부경대학교
- Affiliation
- 부경대학교 대학원
- Department
- 대학원 해양공학과
- Advisor
- 김윤태
- Table Of Contents
- CHAPTER 1: INTRODUCTION 1
1.1 General 1
1.2 Purpose and application of vertical drains 3
1.3 Overview of PVD-improved construction works 5
1.4 Objectives and the scope of study 8
1.5 Organization of the thesis 10
CHAPTER 2: LITERATURE REVIEW 12
2.1 History and Development of Vertical Drains 12
2.2 Parameters related to PVDs performance 14
2.2.1 Equivalent drain diameter 14
2.2.2 Mandrel Size and Shape 15
2.2.3 Installation Procedure 16
2.2.4 Drain spacing and influence zone 17
2.2.5 Soil disturbance caused by PVD installation and discharge capacity 18
2.3 Soil disturbance effect 19
2.3.1 Soil disturbance generation 19
2.3.2 Analytical models of soil disturbance 19
2.3.3 Estimation of the smear zone properties 23
2.3.4 Difference between experimental and field permeability in smear zone 24
2.4 Discharge capacity 25
2.4.1 Definition of discharge capacity of drain 26
2.4.2 Discharge capacity requirement of prefabricated vertical drains 26
2.4.2.1 Discharge capacity from drain resistance approach 27
2.4.2.2 Discharge capacity based on the discharge in the PVD 28
2.4.3 Discharge capacity reduction with depth and time 29
2.5 Theory of vertical consolidation 35
2.5.1 General 35
2.5.2 One-dimensional consolidation test 38
2.5.3 Calculation of the ultimate consolidation settlement 41
2.5.4 Secondary consolidation settlement 43
2.6 Theory of radial consolidation with vertical drain 44
2.6.1 General 44
2.6.2 Analytical solution considering smear zone effects 47
2.6.3 Analytical solution considering discharge capacity reduction effects 50
2.7 Large (finite) strain theory for radial consolidation 52
2.7.1 Large strain governing equation with radial flow 52
2.7.2 Relationship between large-strain effect and vertical strain 54
2.8 Plane strain consolidation model of PVD-installed deposit 55
2.8.1 One-Dimensional drainage elements (1-D drainage element) 56
2.8.2 Macro-element formulation (Sekiguchi et al. 1986) 57
2.8.3 kve method (Chai et al. 2001) 57
2.8.4 Modelling PVD in plane strain by solid element 58
2.8.4.1 Method of Shinsha et al. (1982) 58
2.8.4.2 Method of Indraratna and Redana (1997) 58
2.8.4.3 Method of Kim and Lee (1997) 60
2.9 Finite element method in consolidation 61
2.9.1 General 61
2.9.2 Plaxis 2D software 62
2.10 Material models 63
2.10.1 Morh-Coulomb model 63
2.10.2 Soft soil model 65
2.10.2.1 Isotropic states of stress and strain 65
2.10.2.2 Yield function for triaxial stress state 66
2.11 Summary 67
CHAPTER 3: AN ANALYTICAL MODEL FOR CONSOLIDATION OF PVD-INSTALLED DEPOSIT CONSIDERING SOIL DISTURBANCE 70
3.1 General 70
3.2 A simple analytical solution for an axisymmetric unit cell with soil disturbance 71
3.2.1 A nonlinear distribution of hydraulic conductivity and compressibility 71
3.2.2 Analytical solution 76
3.2.3 Analysis results and comparisons 80
3.3 Application to field behavior 86
3.3.1 Field conditions 86
3.3.2 Consolidation analysis 90
3.4 Summary and conclusion 95
CHAPTER 4: RADIAL CONSOLIDATION OF PVD-INSTALLED DEPOSIT WITH DISCHARGE CAPACITY REDUCTION USING LARGE STRAIN THEORY 97
4.1 General 97
4.2 A large-strain radial consolidation equation for PVD-installed deposits 100
4.2.1 Governing Equations 100
4.2.2 Overconsolidated soils 105
4.3 Effects of various parameters on consolidation behavior 106
4.3.1 The discharge capacity reduction factor 107
4.3.2 Disturbance degree of hydraulic conductivity 108
4.3.3 The Cc/Ck ratio 109
4.3.4 Initial effective stress of a soft deposit 110
4.4 Application to a test embankment 113
4.4.1 A test embankment at Saga Airport 113
4.4.2 A consolidation test of large block sample 118
4.5 Summary and conclusions 120
CHAPTER 5: CONSOLIDATION BEHAVIOR OF PVD-INSTALLED DEPOSIT CONSIDERING DISCHARGE CAPACITY REDUCTION WITH DEPTH 122
5.1 General 122
5.2 Analytical models of axisymmetric unit cell with a varied discharge capacity 123
5.2.1 Varied discharge capacity with a nonlinear distribution 123
5.2.2 Comparison of solutions 125
5.3 A proposed k've method considering a varied discharge capacity 129
5.4 Verification of analytical models with varied discharge capacity with numerical analysis 130
5.5 Summary and Conclusion 136
CHAPTER 6: AN EQUIVALENT PLANE STRAIN MODEL OF PVD-IMPROVED SOFT DEPOSIT CONSIDERING SOIL DISTURBANCE AND WELL RESISTANCE 138
6.1 General 138
6.2 Formulation of an equivalent 2-D model of PVD-installed deposit 139
6.2.1 Equivalent width of vertical drain in 2-D model 140
6.2.2 Equivalent horizontal permeability in 2-D model 142
6.3 Application to a test embankment 144
6.3.1 Test embankment on soft clay deposit in eastern China 145
6.3.2 Test embankment on soft clay in Malaysia 155
6.3.3 Comparison three-dimension (3-D) numerical simulation 161
6.4 Summary and conclusion 165
CHAPTER 7: CONCLUSION AND RECOMMENDATIONS 167
7.1 General Summary 167
7.2 Specific observations 168
7.2.1 An analytical model for consolidation of PVD-installed deposit considering soil disturbances 169
7.2.2 Radial consolidation of PVD-installed normally consolidated soil with discharge capacity reduction using large strain theory 169
7.2.3 Analysis of consolidation behavior of PVD-installed deposits considering a varied discharge capacity with depth 170
7.2.4 An equivalent plane strain model of PVD-installed Deposit 171
7.3 Recommendations for application in practice 171
7.4 Recommendations for future work 173
REFERENCES 175
APPENDIX 194
Appendix I 194
Appendix II 197
Appendix III 198
ACKNOWLEDGMENTS 201
CURRICULUM VITAE 203
- Degree
- Doctor
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