VIETNAM NATIONAL UNIVESITY HANOI VIETNAM JAPAN UNIVERSITY HOANG DUY PHUONG ANALYTICAL AND NUMERICAL ANALYSES ON STIFFNESS ENHANCEMENT OF GROUND IMPROVED BY HEAD-ENLARGED CDM COLUMNS MAJOR: INFRASTRUCTURE ENGINEERING CODE: 8900201.04QTD RESEARCH SUPERVISOR Dr. NGUYEN TIEN DUNG MASTER’S THESIS Hanoi, 2020 LUAN VAN CHAT LUONG download : add luanvanchat@agmail.com TABLE OF CONTENTS ABSTRACT. LIST OF TABLES. LIST OF FIGURES.
LIST OF ABBREVIATIONS. General introduction of deep mixing method.2 Necessity of research .3 Objective and Scope of research .1 Objective of the study .2 Scope of the study. 3 CHAPTER 2: LITERATURE REVIEW.1 Overview of deep mixing method .1 Brief view of deep mixing method .2 Application of CDM .4 Equipment and machine .6 Fixed type and floating type improvement .2 Improvement of conventional CDM method .1 T-shaped soil- cement column .2 The PF method .3 Theory of settlement evaluation .1 The equivalent elastic modulus and 3D settlement of composite grounds .4 Theory of numerical method .1 Preliminaries on material modelling .2 Linear elastic model .3 Mohr-Coulomb model .4 Hardening soil model .5 Soft soil model .2 Analyses using analytical method .3 Analyses using numerical method. 38 CHAPTER 4: LABORATORY AND FIELD TEST .1 Introduction of Samse project .1 General information of project .2 The PF groups .3 Soil profile and footing parameters .2 Laboratory tests for Samse project.
43 LUAN VAN CHAT LUONG download : add luanvanchat@agmail.3 Static load test on PF groups .1 The geometry and installation PF groups .2 Installing strain gauges .4 Static load test on single PF column. 49 CHAPTER 5: SETTLEMENT ANALYSIS AND RESULTS .1 Settlement analyses using elastic theories .2 Analyses for Ideal case and JEF case .3 Results and discussions .2 Settlement analyses using nonlinear models .1 Analyses for ideal case .2 Analyses for the experimental single PF column.3 Analyses for PF groups at SAMSE project. 63 CHAPTER 6: CONCLUSIONS AND RECOMMENDATIONS .2 Limitations and suggestions. 76 LUAN VAN CHAT LUONG download : add luanvanchat@agmail.com ABSTRACT Point Foundation (PF) method is an advanced technology introduced by EXT Co.
Ltd company from Korea, which has more advantages than CDM method. The shape of PF columns makes a big difference in settlement compared to conventional CDM. This study presents a comparative study on stiffness enhancement of grounds improved by Point Foundation method and by the conventional CDM method using analytical and numerical analyses. In addition, the analysis results are compared with experimental program.
The stiffness enhancement is evaluated through induced settlement values under four shallow footing cases, of which one is ideally assumed and the other is an actual footing constructed. Results from both analytical analysis and numerical analysis, in which elastic models are used, indicate that in general the PF method produces a more proper stiffness distribution with depth, which in turn results in smaller settlement values. Numerical analysis results also indicate that when only soil area under the footing is improved settlement of the footing is significantly larger than that on ground improved entirely, the case of theoretical elastic soil model. This is attributed to the influence of larger horizontal displacement around the footing.
Results from numerical analysis, in which inelastic model used, settlement of shallow footing on PF columns is smaller settlement of conventional CDM columns for the same ground model under certain conditions. By true 3D model of column and soil, when the load-settlement is still in relatively linear range, the settlement values from the equivalent soil model and true 3D column and soil model are relatively equal. This may suggest the equivalent soil model can be used in practice as it has been used in the elastic analyses. PF columns has been analyzed the true behavior between columns and soil (shape of PF column, interaction between column and soil), the results analysis show that when analyzing settlement of shallow footings on PF LUAN VAN CHAT LUONG download : add luanvanchat@agmail.com columns in soft clay, special attention should be paid to the stiffness ratio between PF column and soil.
LUAN VAN CHAT LUONG download : add luanvanchat@agmail.com ACKNOWLEDGEMENTS I would like to express my sincere appreciation for the lecturers of Master of Infrastructure Engineering Program for their help during my undergraduate at Vietnam Japan University (VJU). First of all, I am very grateful Dr. Nguyen Tien Dung, who guided me to conduct this thesis for the part one year. He spent a lot of time telling me complicated issues in geotechnical engineering.
Not about knowledge, he also taught me valuable lesson about the seriousness and carefulness in scientific research. These valuable lessons will follow me throughout the future study. I would like to acknowledge the sincere inspiration from Prof. Nguyen Dinh Duc and Prof.
Their lectures covered not only specialist knowledge but also the responsibility and mission of a new generation of Vietnam. I am grateful to Dr. Phan Le Binh for his support in the last two years since I have studied at Vietnam Japan University. Thanks to him, I have learned the professional courtesy of Japanese people as well as Japanese culture.
I would also like to acknowledge the staff of Vietnam Japan University, Mr. Bui Hoang Tan for their help and support. I would also like to thank Prof. Junichi Koseki, Assoc.
Kenji Watanabe, Assist Prof. Hiroyuki Kyokawa as well as other members of Koseki lab, where I had 80 meaningful days internship at The University of Tokyo. It was very helpful to me. Special thanks to Associate professor Nguyen Chau Lan, lecturer at University of Transport and Communication.
His explanations in geotechnical engineering helped me a lot in this study. His successful way in research encouraged me more than anything else. Thanks to Dr. Nguyen Cong Oanh (Vietnam Academic for Water Resources), he explained in detail the complex problems in finite element method for geotechnical engineering.
Finally, Thanks are due to my family, who are always and support me in studies and research. LUAN VAN CHAT LUONG download : add luanvanchat@agmail.com LIST OF TABLES Table 2.1 Typical properties of Stabilized soil (wet method) (Modified from Elias et al.2 Typical Properties of Lime–Cement Stabilized Soils (Dry Method) (Modified from Elias et al.1 Unconfined compression test results .2 Strength parameters of samples collected from the PF column.1 Input parameters for calibration analysis .2 Input parameters for settlement analysis .3 Input parameters for the single PF column .4 Material model and parameter used for Samse factory project. 64 LUAN VAN CHAT LUONG download : add luanvanchat@agmail.com LIST OF FIGURES Figure 1.1 Configuration of improved CDM columns: (a) Point foundation (PF) (Nguyen et al. 2019a): (b) T-shape column (Liu et al.1 Available ground improvement methods for different soil types (modified from Schaefer et al.2 Classification of deep mixing method (Kitazume & Terashi, 2013) .3 Equipment of deep mixing method (DJM machine) .4 Drilling machine (left) and Mixing shaft and blades of DJM machine (right) 11 Figure 2.5 Machine has two mixing shafts and Binder Plant for DJM method (by the courtesy of Dry Jet Mixing Association) .6 Type of ground improvement (Kitazume & Terashi, 2013) .7 The T-shaped soil cement column overlain by embankment (Song-Yu at el, 2012) .8 Displacement of soil under TDM and SCC (Yaolin et al.9 Load- settlement curves of conventional DCM and TDM pile from physical model test (Chana Phutthananon et al, 2012) .10 Site construction of PF method .11 Flexible rectangular loaded area.12 General three demensional coordinate systems and sign convention for stress .13 Basic ideal of an elastic perfectly plastic model (Plaxis manual) .14 The Mohr-Coulomb yield surface in the principal stress space (c=0) .15 Hyperbolic stress- strain curve (Ducan & Chang, 1970) .16 Stress circles at yield (Plaxis manual) .17 Relationship between initial tangent modulus and confining pressure .18 Unloading and reloading of silica sand under drain triaxial test consolidation (Ducan and Chang 1970) .19 Hyperbolic stress–strain relationship in primary loading for a standard drained triaxial test (Schanz, 1999) .20 Representation total yield of the HS model in principle space stress for cohesionless soil.21 Yield surface of hardening model (Schanz et al.
1 Configuration of CDM and PF columns. 1 Plan view of SAMSE factory project. 2 Plan view of three PF groups .3 Shape of PF columns: (Left) Group 1 (LPF=8.4 Soil profile of SAMSE factory project .5 Collection of mixed cement- soil samples. 45 LUAN VAN CHAT LUONG download : add luanvanchat@agmail.7 Relationship between secant modulus of elasticity and unconfined compressive strength (SAMSE project) .8 Static load test on instrumented PF groups .9 Test installation: (a) the geometry of PF columns, (b) increment load applies on steel plate, (c) displacement sensors on steel plate and groundb.10 Strain gauge installation: (a) installation of sensors along the depth of PF, (b) setting up sensors into PF, (c) strain gauge instruments, (d) sensor in PF .11 Soil profile at Songdo site (Kim et al.12 Configuration of the instrumented column (Kim et al.13 Instrumentations implemented on variable cross-section soft ground reinforced foundation (Kim et al.1 Foundation and soil domain in the numerical analysis .2 Comparison of vertical stress profiles obtained from analytical and numerical analyses .3 Soil profile under the examined footings (Ideal case).4 Soil profile under the examined footings (JEF project) .5 Cross-sectional and plan views of the examined footing at JFE project.6 Settlement value from analytical method for Ideal case .7 Settlement value from analytical method for JEF case .8 Variation of Scorr,PF,min/Scorr,CMD ratio.9 Settlement values from analytical and numerical analyses for Ideal case .10 Settlement values from analytical and numerical analyses for JEF project .11 Settlement analysis from numerical method for ideal case .12 Settlement analysis from numerical method for JEF case .13 Load- settlement curves from MC model .14 Load settlement curves from Numerical method for PF column and conventional CDM .15 Load settlement curves from Numerical method for PF columns and CDM columns using equivalent material (E50=150qu) .16 Load settlement curves from Numerical method for PF groups and CDM groups using true 3D model of PF columns and soil .17 Settlement profiles with depth of footings on PF and CDM columns from numerical method using equivalent material model (q = 800 kPa) .18 Load settlement curves from Numerical method for PF columns and conventional CDM columns (Optimal shape design for PF columns) .19 Variation of settlement () and effective vertical stress (v) at the toe of CDM and PF columns obtained from numerical analysis using true 3D model .20 Mohr- Coulomb failure criterion.
76 LUAN VAN CHAT LUONG download : add luanvanchat@agmail.com LIST OF ABBREVIATIONS as Improvement area ratio ascc Improvement area ratio of conventional CDM column CDM Cement deep mixing method c (c’) Cohesion strength Cc Compression index Cs Swelling index D Diameter of conventional soil cement column (m) Dh Diameter of cap of HCC (m) Df Embedded depth (m) Dt Diameter of tail of HCC (m) eo Initial void ratio Ei Initial tangent modulus Eoed Oedometric modulus E50 Scant elastic modulus of soil at 50 percent (kPa) Eu Undrained elastic modulus of soil (kPa) Eur Unloading and reloading Young’s modulus Ec Elastic modulus of soil cement column (kPa) Ecomp Elastic modulus of improved ground (kPa) Es Elastic modulus of soil (kPa) E’s Young’s modulus in term of effective stress HCC Head-enlarged soil cement column HS Hardening soil model L Length of conventional soil cement column (m) Lc Length of cone of PF column (m) Lh Length of head of PF column (m) Lt Length of tail of PF column (m) Shape factor for Cam clay ellipse/slope of critical state M line MC Mohr Coulomb model Ms Constrained modulus of soil (kPa) NC Normal consolidation OCR Over consolidation ratio PF Point foundation PI Plasticity index (%) qu Unconfined compressive strength (kPa) LUAN VAN CHAT LUONG download : add luanvanchat@agmail.