(Luận văn) compressibility characteristics of soft clays in the red river delta

VIETNAM NATIONAL UNIVERSITY, HANOI VIETNAM JAPAN UNIVERSITY KHIN PHYU SIN COMPRESSIBILITY CHARACTERISTICS OF SOFT CLAYS IN THE RED RIVER DELTA MASTER’S THESIS VIETNAM NATIONAL UNIVERSITY, HANOI VIETNAM JAPAN UNIVERSITY KHIN PHYU SIN COMPRESSIBILITY CHARACTERISTICS OF SOFT CLAYS IN THE RED RIVER DELTA MAJOR: INFRASTRUCTURE ENGINEERING CODE: 8900201.04 QTD RESEARCH SUPERVISOR: Dr NGUYEN TIEN DUNG Hanoi, 2022 PLEDGE I have read and understood the plagiarism violations I pledge with personal honor that this research result is my own and does not violate the Regulation on prevention of plagiarism in academic and scientific research activities at VNU Vietnam Japan University (Issued together with Decision No 700/QD-ĐHVN dated 30/9/2021 by the Rector of Vietnam Japan University) AUTHOR OF THE THESIS Khin Phyu Sin ABSTRACT Together with the development, requirement of rigorous foundation designs plays a vital role in the construction of sustainable infrastructure structure system in Song Hong or Red River Delta (RRD) as it is the hub of various economic activities Therefore, a comprehensive understanding about compressibility characteristics of soft clays from RRD not only could prevent geotechnical engineering problems but also could extend the benefit of structural designs in both economical and safety point of views This study mainly focuses on the determination of coefficient of consolidation with vertical and horizontal drainage directions as those parameters are highly essential for the ground improvement works using PVDs For this, laboratory tests and CPTu tests at four study sites in the delta were carried out to study the characteristics Eight methods for determining coefficient of consolidation with a peripheral drain (cr,PD) and that with a central drain (cr,CD) were reviewed and applied to the samples from the four test sites Analysis results indicate that the non-graphical method results in the highest reliability whereas the Log-log and Steepest tangent methods result in the poorest reliability Based on the analysis results from consolidation test samples obtained from different geological locations in RRD, the ratio of cr,PD /cr,CD of intact and remolded samples varies from 0.6 to 0.8 and from 0.4 to 0.6, respectively The experimental ratio cr,PD / cr,CD value of intact samples is smaller than that from analytical solution (for n = 2.21) of approximate 1.0 and this is mainly attributed to the influence of drainage length of soil in two drainage types Numerical analysis results of consolidation tests (n = 2.21) show that cr,PD /cr,CD ratio value on average is similar to those experimentally obtained from the intact samples and the ratio varies significantly with the variation of n value The preconsolidation stress obtained from consolidation test and from CPTu-based correlation for the test sites indicate that the soft clays in the delta are predominantly low plasticity normally consolidated (NC) Additionally, correlations of Cc/e0 = 0.3864 and Cr/Cc = 0.1208 can be suggested for the clays in the delta ACKNOWLEDGEMENTS Firstly, the author would like to give her special gratitude to the JAIF scholarship for giving an opportunity to have such a kind of great learning experience in VJU, especially in MCE Furthermore, the author deeply indebted to Prof Nguyen Dinh Duc (MCE Director), Prof Hironori Kato (MCE co-director), Dr Nguyen Tien Dung (MCE coordinator), Assoc Prof Takeda Shinichi (MCE JICA expert), and Dr Nguyen Ngoc Vinh (MCE lecturer) for their kind supports, guidance, and recommendations in various aspects including during the lecture time and research period Moreover, I’m gratefully recognized the help and supports from Ms Hoa Bui (MCE program assistant), Mr Bui Hoang Tan (MCE Lab Technical) and Ms Pham Lan Huong (temporary program assistant) Finally, I would like to express my deepest gratitude to my supervisor Dr Nguyen Tien Dung (MCE coordinator) for his patient and enthusiastic supports, specific advice and guidance on every step of performing the research works Additionally, very special thanks to my supervisor and his company (FECON) for letting me to apply the data from the study sites TABLE OF CONTENTS LIST OF TABLES .i LIST OF FIGURES ii LIST OF ABBREVIATIONS .vi CHAPTER INTRODUCTION 1.1 General 1.2 Problem statement 1.3 Necessity of the study 1.4 Objectives .4 1.5 Scope of the study 1.6 Outline and structure of the thesis 1.6.1 Outline of the thesis 1.6.2 Structure of the thesis CHAPTER LITERATURE REVIEW .8 2.1 Geographical conditions of the RRD 2.2 Geological conditions of the RRD 2.3 Consolidation 12 2.3.1 Three stages of deformation in accordance with time during consolidation process 12 2.3.2 Consolidation theory (vertical and horizontal drainage cases) 14 2.4 Standardized methods to determine vertical coefficient of consolidation, cv .19 2.5 Methods to determine radial or horizontal coefficient of consolidation for central drain (CD), cr,CD case 19 2.6 Methods to determine radial or horizontal coefficient of consolidation for peripheral drain (PD) case, cr,PD 21 2.7 Compression index (Cc) 22 2.8 Recompression index (Cr) 23 2.10 Overconsolidation ratio (OCR) 25 2.11 Literature review about the previous study 27 CHAPTER METHODOLOGY 31 3.1 Collecting required information about the geography and geological condition of the RRD 31 3.2 Collecting required data from the study sites 31 3.3 Analyzing the data (radial or horizontal coefficient of consolidation, crPD or CD) 32 3.3.1 Orientation of the methods used in this study for the determiation of radial or horizontal cefficient of consolidation, crPD or CD 32 3.3.2 Ranking the methods 33 3.3.3 Evaluation of the correlation between cr,CD and cr,PD 35 3.3.4 Finding influent facts that cause the correlation between cr,PD and cr,CD is not equal to one 36 3.4 Analyzing the data (Coefficient of vertical consolidation, cv) 41 3.5 Evaluation of pꞌ, OCR, C, OCR, Cc, Cr 41 CHAPTER STUDY SITES AND ANALYSIS RESULTS 43 4.1 Study sites 43 4.1.1 DVIZ site and field test program 43 4.1.2 VSIP site and field test program 44 4.1.3 KC site and field test program 45 4.1.4 TPP site and field program 45 4.1.5 Laboratory tests 46 4.2 Soil profiles from the four study sites 49 4.2.1 Physical properties profiles 49 4.2.2 CPTu-based soil profiles 51 4.3 Analysis results of ranking the eight methods used for cr,CD (or cr,PD) determinations 52 4.3.1 Results of R and Root Mean Squared Error (RMSE) for intact samples 52 4.3.2 Results of R and Root Mean Squared Error (RMSE) for remolded samples 61 4.4 Evaluation of correlation between cr,CD and cr,PD 70 4.4.1 Correlation between cr,CD and cr,PD (Intact samples) 70 4.4.2 Correlation between cr,CD and cr,PD (Remolded samples) 72 4.4.3 Conclusion for the Correlation between cr,CD and cr,PD 74 4.4.4 Finding influent facts that cause the correlation between cr,PD and cr,CD is not equal to one 74 4.5 Evaluation of correlation between cr,CD and cv 75 4.5.1 Correlation between cr,CD and cv (Intact samples) 76 4.5.2 Correlation between cr,CD and cv (Remolded samples) 76 4.5.3 Conclusion for the Correlation between cr,CD and cv 77 4.6 Evaluation of correlation between cr,PD and cv 77 4.6.1 Correlation between cr,PD and cv (Intact samples) 77 4.6.2 Correlation between cr,PD and cv (Remolded samples) 78 4.6.3 Conclusion for the Correlation between cr,PD and cv 79 4.7 Evaluaion of preconsolidation pressure (pꞌ, OCR, C), compression index (Cc), recompression indexes (Cr), and overconsolidtion ration (OCR) 79 CHAPTER CONCLUSIONS AND RECOMMENDATIONS 83 5.1 Conclusions 83 5.2 Recommendations 83 PUBLISHED PAPERS IN PROCEEDINGS 85 RFERENCES 86 APPENDIX 89 LIST OF TABLES Table 2.1 Standardized methods to determine vertical coefficient of consolidation, cv 19 Table 2.2 Existing methods for the determiation of cr from radial consolidatin test with a CD using incremental loading 20 Table 2.3 Existing methods for the determiation of cr from radial consolidatin test with a PD using incremental loading 21 Table 2.4 Soil terminology applied to stress history, FHWQ-NHI-16-072 , 2017) 26 Table 2.5 Differences between previous study and present study 28 Table 3.1 Input parmaeters used in Numerical analysis 39 Table 4.1 Summary table for the number of intact samples from four study sites 48 Table 4.2 Summary table for the number of remolded samples from four study sites 48 Table 4.3 cr,CD results obtained from sample no.18 of KC site 89 Table 4.4 cr,PD results obtained from sample no.18 of KC site 92 Table 4.5 Summary table for the results of R and RMSE values for intact samples (CD case) 54 Table 4.6 Summary table for the results of R2 and RMSE values for intact samples (PD case) 58 Table 4.7 Summary table for the ranked results of the eight methods (Intact samples) 60 Table 4.8 Summary table for the results of R and RMSE values for remolded samples (CD case) 63 Table 4.9 Summary table for the results of R and RMSE values for remolded samples (PD case) 67 Table 4.10 Summary table for the ranked results of the eight methods (Remolded samples) 70 Table 4.11 Summary table for the correlation results between cr,PD and cr,CD for the eight methods (Intact samples) 72 Table 4.12 Summary table for the correlation results between cr,PD and cr,CD for the eight methods (Remoded samples) .74 Table 4.13 Summary table for the correlation results between cr,PD and cr,CD by using Root t method based on the data obtained from PLAXIS software (10k kPa pressure range) 75 Table 4.14 Variation in cr,CD and cr,PD/cr,CD results based on different n vaules (10 kPa) 75 Table 4.15 Summary table for the correlation results between cr,CD and cv with the two standardized method (Intact samples) 76 Table 4.16 Summary table for the correlation results between cr,CD and cv with the two standardized method (Remolded samples) 77 i Table 4.17 Summary table for the correlation results between cr,PD and cv with the two standardized method (Intact samples) 78 Table 4.18 Summary table for the correlation results between cr,PD and cv with the two standardized method (Remolded samples) 79 Table 4.19 Summary table for the number of intact samples available to determine pꞌ, OCR, C, Cr, Cc, and OCR from four study sites 79 Table 4.20 Summary table for the results of pꞌ, OCR, C, Cr, Cc, and OCR from four study sites 95 Table 4.21 Summary table for the correlation results between Cc and e0, and Cc, and Cr 80 ii LIST OF FIGURES Figure 1.1 Dissipation of excess pore water in both horizontal and vertical direction by installing PVD in underlying soft clays layer Figure 1.2 Settlements problems found in a construction site from Hai Phong city owing to the overestimation or underestimation effect of cr values .3 Figure 1.3 Flow chart shows the outline of the thesis (a) general framework of the reseach; (b) flow of the analysis steps .5 Figure 2.1 (a) Topological zoning of the RRD; (b) Three main sectord of RRD zoing according to the origins of its formation (Phach et al., 2020) Figure 2.2 Cross section showing the five depositional Quaternary sediments from Hanoi city area in north-east to south-west direction 10 Figure 2.3 Alluvial delta plain with four paleoshorelines with ages of 3–2.5 Ka: 1.5–1 2— Ka, 0.7–0.5 Ka, and 0.3–0.1 Ka belonging to the highstand systems tract (amhHSTQ ) from Yen et al., 2021 11 Figure 2.4 Location of the seven cores (Tanabe et al., 2006 modified after Tanabe et al., 2003b) .12 Figure 2.5 Spring-cylinder model for consolidation in saturated clays or spring and piston analogy ilustrating the principle of 1D consolidation (Das, 2010) 12 Figure 2.6 Time-deformation plot during consolidation under a given load incrment (Das, 2010) .13 Figure 2.7 Idealized curve of e-log (’pp) from oedometer test for determining compression index (after Mayne et al., 2001) 22 Figure 2.8 Casagrande (1936)’s method (Dung and Giao, 2005) .24 Figure 2.9 Silvs (1970)’s method (Dung, and Giao, 2005) 25 Figure 2.10 First-order relationship for preconsolidation stress from net cone resistance in clays, Mayne, 2007) 27 Figure 3.1 Sample collection for radial coefficient of consolidation, cr,PD or CD .31 Figure 3.2 Flow chart shows the orientation of the method that are used in this study 32 Figure 3.3 Flow chart shows the analyzed steps used for the determination of coefficient of radial consolidation, cr,PD or CD 33 Figure 3.4 Example of time (t) and measured settlement (m) data curve for the determination of cr,CD (or cr,PD) from KC site (Non-graphical method) 34 Figure 3.5 Example of (m) vs e graph for 800 kPa pressure range (Non-graphical method) 34 Figure 3.6 Probability density function of a normal random variable with mean () and variance () 35 Figure 3.7 Example of cr,CD/cr,PD vs f(x) curve from full-match method (intact sample) .36 Figure 3.8 Example of cr,CD vs cr,PD curve from full-match method (intact sample) .36 Figure 3.9 Variation in n values with changes in sandstone dimensions 37 Figure 3.10 Soil model construction in PLAXIS software for PD case 37 iii