Title Page
ABSTRACT
국문 초록
Contents
NOMENCLATURE 18
CHAPTER 1. INTRODUCTION 20
1.1. Background and Motivation 20
1.2. Objectives and Organization 23
CHAPTER 2. LITERATURE REVIEW 24
2.1. Analytical and Experimental Research on Soil Plug 24
2.2. Numerical Research on the Analysis of Pile Foundation 27
2.2.1. Finite element methods 27
2.2.2. Discrete element methods 33
2.3. Influencing Factors of Soil Plug Formation 42
2.3.1. Effect of pile geometry 42
2.3.2. Effect of soil conditions 43
2.3.3. Effect of driving methods 43
CHAPTER 3. FORMULATION OF DEM 45
3.1. Schematic Formulation of Particle Flow Code 45
3.2. Model Components 47
3.2.1. Ball and clump 47
3.2.2. Wall 47
3.3. Contact Model 48
3.3.1. Formulation of linear contact model 49
3.3.2. Rolling resistance linear contact model 54
CHAPTER 4. NUMERICAL MODELING 56
4.1. DEM Modeling 56
4.1.1. Preparation of test material 56
4.1.2. Extreme void ratios 59
4.1.3. Sample preparation 61
4.1.4. Representation of the open-ended pile 66
4.2. Validation of DEM Model 70
4.2.1. Validation of soil-soil interaction 70
4.2.2. Verification of soil-pile interaction 73
4.3. Variation of Pile Diameter 75
CHAPTER 5. RESULTS AND ANALYSIS 76
5.1. Soil plug length 76
5.1.1. PLR and IFR 76
5.2. Variation of Internal Stress State of Soil Plug 79
5.2.1. Local Stress State of the Soil Plug 88
5.3. Effect of Pile Diameter 91
5.3.1. Effect on soil plug length 91
5.3.2. Influence on plug length indices 92
5.3.3. Impact on the internal stress state of the soil plug 94
CHAPTER 6. CONCLUSIONS 96
REFERENCES 99
Table 4.1. Grain size indices of Ottawa F-55 sand and the granular model in DEM 58
Table 4.2. Summary of publications on DEM analysis of penetration processes 69
Table 4.3. Results from biaxial compression test 71
Table 4.4. Input parameters of contact models in the DEM analysis 72
Table 4.5. List of model names and their features 75
Table 5.1. Design codes for open-ended pile 95
Figure 2.1. Photograph of the open-ended piles with pressure sensors 26
Figure 2.2. Overview of FEM modeling and its open-ended pile in axisymmetric conditions 30
Figure 2.3. Plot of applied force on the OEP; (a) impact driving (b) vibratory driving 30
Figure 2.4. Arrangements of soil layering 31
Figure 2.5. Distribution of the coefficient of lateral earth pressure under different end- bearing conditions versus the normalized distance from the pile tip 31
Figure 2.6. PLR against normalized penetration depth from the field test and numerical simulation 32
Figure 2.7. Distribution of induced (a) vertical and (b) radial stress inside the pile to the normalized plug length 32
Figure 2.8. Outline of the model of DEM-BEM coupling 37
Figure 2.9. Particle-crushing scheme induced by tensile stress: (a) Non-crushing (b) Limit stress state of crushing (c) New arrangements of particles after crushing 37
Figure 2.10. Displacement field induced by pile penetration 38
Figure 2.11. Interpretation of shear failure mode considering: (a) Terzaghi theory (b) Biarea & Hu theory (c) Berezanteva & Vesic theory 38
Figure 2.12. Rotations of particles resulting from OEP installation at different interface friction angles: (a) 18° (b) 5.7° (c) 0° 39
Figure 2.13. Overview of the DEM model including the OEP configuration: closely overlapped clump 39
Figure 2.14. Deformation of soil plug when (a) 1/3 penetration (b) 2/3 penetration (c) full penetration 40
Figure 2.15. Displacement control of open-ended pile simulating installation methods in DEM 40
Figure 2.16. Results of plug length due to pile penetration 41
Figure 2.17. Results of the inner state of soil plug due to pile penetration 41
Figure 3.1. Calculation procedure of PFC for each cycle 46
Figure 3.2. Internal force and moment acting on a contact plane 48
Figure 3.3. Symbols of rheological elements with their corresponding parameters 49
Figure 3.4. Formulation of linear contact model 51
Figure 3.5. Coordinate systems at each contact for 2D and 3D models 52
Figure 3.6. Dynamics of contact in terms of contact plane with relative displacement 52
Figure 3.7. Piecewise functions representing force-displacement law calculating themagnitudes of (a) Fnl: normal force versus surface gap (b) Fsl: shear force versus relative...[이미지참조] 53
Figure 3.8. Update of shear spring force and relative shear displacement 53
Figure 3.9. Dynamics of contact in terms of contact plane with relative rotational displacement 55
Figure 4.1. Flow of the numerical analysis on the soil plug 56
Figure 4.2. Particle size distribution curves of Ottawa F-55 sand and the granular assembly in PFC2D 58
Figure 4.3. Methods of measuring extreme void ratios in DEM 60
Figure 4.4. Suspended particles inside the soil container without any contact 64
Figure 4.5. Initial state of the soil sample depicted with a contact force chain in DEM 64
Figure 4.6. Measurement circles within the soil sample, colored with measurement circles 65
Figure 4.7. Initial distribution of stress, K₀, and porosity 65
Figure 4.8. Overall appearance and dimension of the pile in the model 67
Figure 4.9. Pile placed into the sandbed by 40 mm 68
Figure 4.10. Displacement control of the open-ended pile in simulation: 12 stages 68
Figure 4.11. Peak internal friction angle from the numerical biaxial compression test on the set of prepared soil elements in DEM 71
Figure 4.12. Model pile test results against penetration depth: (a) Cumulative blow count (b) Soil plug length 74
Figure 5.1. Progressive state of the model by pile penetration 77
Figure 5.2. Plug length resulting from the numerical simulation 78
Figure 5.3. Plug length indices: (a) PLR; (b) IFR 78
Figure 5.4. Horizontal and vertical stress distribution within the soil plug, and contact force chain at each penetration depth of: (a), (b) 162 mm; (c), (d) 236 mm 82
Figure 5.5. Horizontal and vertical stress distribution within the soil plug, and contact force chain at each penetration depth of: (a), (b) 292 mm; (c), (d) 343 mm 83
Figure 5.6. Horizontal and vertical stress distribution within the soil plug, and contact force chain at each penetration depth of: (a), (b) 389 mm; (c), (d) 432 mm 84
Figure 5.7. Horizontal and vertical stress distribution within the soil plug, and contact force chain at each penetration depth of: (a), (b) 475 mm; (c), (d) 516 mm 85
Figure 5.8. Horizontal and vertical stress distribution within the soil plug, and contact force chain at each penetration depth of: (a), (b) 555 mm; (c), (d) 596 mm 86
Figure 5.9. Horizontal and vertical stress distribution within the soil plug, and contact force chain at each penetration depth of: (a), (b) 633 mm; (c), (d) 670 mm 87
Figure 5.10. Local stress state of the soil plug at the top, middle, and bottom section 89
Figure 5.11. Distribution of lateral earth pressure coefficient inside soil plug at 432 mm and 555 mm penetration stages 90
Figure 5.12. Soil plug length at final penetration depth of each model: (a) Overview; (b) Plug length versus penetration depth 91
Figure 5.13. Effect of pile diameter on soil plug length indices: (a) PLR; (b) IFR 92
Figure 5.14. Correlation between IFR and PLR 93
Figure 5.15. Evolution of stress state of soil plug from various diameters 94