(Luận văn thạc sĩ) remedy solutions for deep seated landslides case studies in lao cai province, vietnam

VIETNAM NATIONAL UNIVERSITY, HANOI VIETNAM JAPAN UNIVERSITY THU ZAR AUNG REMEDY SOLUTIONS FOR DEEP-SEATED LANDSLIDES: CASE STUDIES IN LAO CAI h PROVINCE, VIETNAM MASTER’S THESIS VIETNAM NATIONAL UNIVERSITY, HANOI VIETNAM JAPAN UNIVERSITY THU ZAR AUNG REMEDY SOLUTIONS FOR DEEP-SEATED LANDSLIDES: CASE STUDIES IN LAO CAI h MAJOR: INFRASTRUCTURE ENGINEERING CODE: 8900201.04 QTD RESEARCH SUPERVISOR: Dr NGUYEN CHAU LAN PROVINCE, VIETNAM Hanoi, 2023 h ABSTRACT A landslide is one of the most common geological disasters that occurs in mountainous regions and coastal areas In Vietnam, most landslides and slippage frequently occur in mountainous areas, mainly in Lao Cai province, during the rainy season In 2021, a deep-seated landslide happened during the under construction of retaining structures and the new expressway Lao Cai – Sapa 4D highway road near the new Mong Sen bridge during the rainy season Next, slope failure occurred in near Muong Hoa valley, on Road No.152 in 2021 In literature, there is limited research to study about the remedy solutions against landslides under rainfall and earthquake conditions in these areas This research mainly focuses two key objectives: 1) the simulation of the slope stability by using numerical analysis with LEM (GEO-SLOPE) and FEM (PLAXIS); 2) finding the effectiveness countermeasures for remedy solutions against landslide failure triggered by heavy rainfall and earthquake along the highway in Lao Cai province This study utilizes three remedy solutions: 1) slope cutting method; 2) h retaining method; and 3) anchoring method to study the effect of several countermeasures Based on the analysis results from the numerical simulations of LEM and FEM under rainfall and earthquake conditions on the initial slope, the estimated failure surface occurs in the soil layer or above the bedrock layer, which indicates the instability of the slope and is consistent with the actual field results This study shows that the numerical analysis both LEM and FEM model allow to predict the sliding surface of landslides based on the measured parameters of soil layers The numerical analysis and construction feasibility of three remedy solutions in the case of rainfall and earthquake conditions indicate that, as expected, the F.S values are highest and ground anchors passed through the slip failure surface and smallest shade in an anchoring method compared with the slope cutting method and retaining method Thus, an anchoring method is a suitable remedy solution against landslides under rainfall and earthquake conditions Besides, this research reveals that the FE analyzes of the ground motion acceleration earthquake results are dramatic decreases compared with the pseudo-static earthquake Moreover, this study indicates that the FEM (PLAXIS) is more accurate than the LEM (GEO-SLOPE) for practical design works h 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 First and foremost, I would like to express my deepest gratitude to my respected and diligent supervisor Dr Nguyen Chau Lan (UTC, Hanoi, Vietnam) for his patient and enthusiastic supports, specific advice and guidance on every step of performing the research works He spent hours trying to explain to me anytime even when being very busy 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 h 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) And also, special thanks to Mr Kieu Quang Huy (staff from UCT-Geo), I got many helps and supports from him for my research analysis Additionally, I would like to extend further thanks to my classmates They helped me along staying in Vietnam to complete my research successfully Finally, I would like to express my deep gratitude to my family members for the support and belief on every step of my life, without them I could not have been in this place today TABLE OF CONTENTS h LIST OF TABLES i LIST OF FIGURES ii LIST OF ABBREVIATIONS v CHAPTER INTRODUCTION 1.1 General background 1.2 Location and detail conditions of the study area 1.2.1 Case study 1: Road No.155, near new Mong Sen bridge, Trung Chai commune, Sapa town, Lao Cai province 1.2.2 Case study 2: Road No.152, near Muong Hoa valley, Cau May commune, Sapa town, Lao Cai province 1.3 Research problem 1.4 Research question 1.5 Research objectives 1.6 Scope of the research 1.7 Outline and structure of the thesis 10 1.7.1 Outline of the thesis 10 1.7.2 Structure of the thesis 11 1.8 Findings and Research contributions 12 CHAPTER LITERATURE REVIEW 13 2.1 Literature review of case studies 13 2.1.1 Literature review 13 2.1.2 Historical background of earthquake in Vietnam 17 2.2 Landslides causes and triggering mechanisms of Lao Cai province, Vietnam 19 2.3 Classifications of countermeasure for deep-seated landslides 21 2.4 Slope stability analysis and methods 25 2.5 Limit Equilibrium Method (LEM) 26 2.6 Finite Element Method (FEM) 30 2.7 Previous studies of slope stability using LEM (GEO-SLOPE) and FEM (PLAXIS) for Lao Cai area 33 CHAPTER DATA COLLECTION AND RESEARCH METHODOLOGY 35 3.1 Research methodology 35 3.2 Data collection 37 3.2.1 Field investigation 37 3.2.2 Topography and geology investigation 38 3.2.3 Geological bore hole investigation 41 3.2.4 Metrological data collection 43 3.2.5 Seismic data collection 44 3.3 Laboratory testing 45 3.3.1 Laboratory testing results 46 h 3.4 Input parameters for LEM and FEM model of two case studies 48 3.5 Model geometry to analyze slope stability by LEM and FEM 56 3.5.1 Model geometry of case study (Mong Sen) 56 3.5.2 Model geometry of case study (Muong Hoa) 57 3.6 Numerical modelling of case study (Mong Sen) based on LEM and FEM 57 3.6.1 Numerical modelling of LEM 57 3.6.2 Numerical modelling of FEM 59 3.7 Numerical modelling of case study (Muong Hoa) based on LEM and FEM 62 3.7.1 Numerical modelling of LEM 62 3.7.2 Numerical modelling of FEM 63 CHAPTER ANALYSIS RESULTS AND DISCUSSIONS 65 4.1 Analysis results of Case Study (Mong Sen) based on LEM and FEM 65 4.1.1 Case 1: Normal condition of initial and remedy solutions slope stability result 65 4.1.2 Case 2: Rainfall condition of initial and remedy solutions slope stability result 69 4.1.3 Case 3: Earthquake condition of initial and remedy solutions slope stability result 73 4.1.4 Case 4: Ground motion and pseudo-static earthquake condition of initial and remedy solutions slope stability results based on FEM 77 4.2 Analysis results of Case Study (Muong Hoa) based on LEM and FEM 78 4.2.1 Case 1: Normal condition of initial and remedy solutions slope stability result 78 4.2.2 Case 2: Rainfall condition of initial and remedy solutions slope stability result 81 4.2.3 Case 3: Earthquake condition of initial and remedy solutions slope stability result 85 4.2.4 Case 4: Ground motion and pseudo-static earthquake condition of initial and remedy solutions slope stability results based on FEM 88 4.3 Discussions 89 CHAPTER CONCLUSIONS AND RECOMMENDATIONS 93 5.1 Conclusions 93 5.2 Recommendations 94 RFERENCES 96 APPENDIX 99 LIST OF TABLES h Table 1.1 Types of landslides, abbreviated version of Varnes' classification of slope movements (Varnes, 1978) Table 2.1 Classification of countermeasure for deep-seated landslide (N.C.Koei & JICA, 2007) 21 Table 3.1 Acceleration data from Vietnamese Standard (TCVN 9386-2012) 44 Table 3.2 Physical and mechanical properties of soil layer and rock layer 46 Table 3.3 Physical and mechanical properties of soil layer and rock layer 47 Table 3.4 Input parameters of soil material to input GEO-SLOPE (Case Study 1) 48 Table 3.5 Input parameters of soil material to input PLAXIS 2D (Case Study 1) 49 Table 3.6 Input parameters of soil material to input GEO-SLOPE (Case Study 2) 49 Table 3.7 Input parameters of soil material to input PLAXIS 2D (Case Study 2) 50 Table 3.8 Input parameters of countermeasure to input GEO-SLOPE .50 Table 3.9 Input parameters of countermeasure to input PLAXIS 2D 51 Table 3.10 Input parameters of SWCC in SEEP/W for case study (Mong Sen) 52 Table 3.11 Input parameters of Hydraulic Conductivity in SEEP/W for case study (Mong Sen) 53 Table 3.12 Input parameters of SWCC in SEEP/W for case study (Muong Hoa) 53 Table 3.13 Input parameters of Hydraulic Conductivity in SEEP/W for case study (Muong Hoa) 53 Table 3.14 Rainfall parameters and Earthquake coefficient for GEO-SLOPE 54 Table 3.15 Ground water flow parameters of soil material for case study (Mong Sen) 55 Table 3.16 Ground water flow parameters of soil material for case study (Muong Hoa) .55 Table 3.17 Rainfall parameters and Earthquake coefficient for PLAXIS 56 i LIST OF FIGURES h Figure 1.1 Schematic illustration of landslides (Varnes, 1978) Figure 1.2 Schematic illustration of the major types of landslide movement (U.S Geological Survey, Reston, Virginia: 2008) Figure 1.3 Location of the study area: Northern region of Vietnam (Map of Vietnam) Figure 1.4 Location of the case study (Mong Sen) Figure 1.5 Location of the case study (Muong Hoa valley) .7 Figure 1.6 Flow chart shows the outline of the thesis (a) general framework of the research; (b) flow of the analysis steps 10 Figure 2.1 Deformation and failure area of (Zhang et al., 2023) 13 Figure 2.2 Part of the road collapsed area of (Islam et al., 2021) 14 Figure 2.3 Pre-event and Post-event of Thae Phyu Kone landslide (Panday & Dong, 2021) 15 Figure 2.4 Landslide body on Halong-Vandon new expressway 15 Figure 2.5 Sliding failure along the Noi Bai – Lao Cai highway 16 Figure 2.6 Location of the landslide site .17 Figure 2.7 Seismic network of Vietnam (L M Nguyen et al., 2012) 18 Figure 2.8 Map of the recorded earthquake in North of Vietnam (L M Nguyen et al., 2012) 19 Figure 2.9 Selection flow chart of countermeasure .26 Figure 2.10 Bishop’s Simplified factor of safety (Calgary, 2020) 28 Figure 2.11 Elastic perfectly plastic model concept 32 Figure 3.1 Methodology flow chart .36 Figure 3.2 Numerical analysis flow chart 36 Figure 3.3 Slope collapsed area for case study (Mong Sen) .37 Figure 3.4 Slope collapsed area for case study (Muong Hoa) 38 Figure 3.5 Geological map of case study (Mong Sen) .39 Figure 3.6 Geological map of case study (Muong Hoa) 40 Figure 3.7 Geological bored hole layout cross section for case study (Mong Sen) 42 Figure 3.8 Geological bored hole layout cross section for case study (Muong Hoa) .42 Figure 3.9 Monthly rainfall and accumulative rainfall data (a) 2021; (b) 2022 43 Figure 3.10 Ground motion recorded from Dien Bien earthquake (2001) 44 Figure 3.11 Geological distribution of bored hole cross section (a) case study (Mong Sen); (b) case study (Muong Hoa) 46 Figure 3.12 Input parameters window for SWCC and Hydraulic Conductivity 54 Figure 3.13 Input parameters window for seismic coefficient in SLOPE/W 54 Figure 3.14 Input parameters window for ground water flow .56 ii Effect of rainfall-induced and earthquake-induced landslide Sapa town, Lao Cai province is the mountainous region and monsoon area Moreover, this area is located in a seismically active zone and near the major faults as indicated in Figure 2.8 In addition, earthquakes occur during rainy periods may increase the scale of landslides This research found out the effect of rainfall and earthquake-induced landslides with and without remedy solution slope and several countermeasures, as presented in Figure 4.36 for case study and Figure 4.37 for case study For the case study (Mong Sen), the F.S results approximately 3% decreased from normal to rainfall condition, and at the condition of normal to earthquake approximately 8% decreased For the case study (Muong Hoa), the F.S results approximately 4% decreased from normal to rainfall condition, and at the condition of normal to earthquake approximately 11% decreased There is a few research about the remedy solutions to stabilize the slope against landslide under rainfall conditions for Lao Cai province (Zhang et al., 2023, Van Tien et al., 2018) In addition, the FEM analysis of the ground motion earthquake results indicated that the F.S values are dramatic decrease in the case of several countermeasures due to the application of dynamic h multiplier option with time variation as the ground motion earthquake Therefore, ground motion should be considered for slope stability and countermeasure selection for remedy solutions Effectiveness of countermeasure In this research, three countermeasure methods proposed the remedy solutions against landslides for two case studies The F.S values obtained from slope cutting method is not greater than required value (F.S = 1.2) under rainfall and (F.S = 1.08) earthquake conditions, the retaining method is over the required value in both rainfall and earthquake conditions, and an anchoring method is more over than the required value under rainfall and earthquake conditions The F.S values obtained from LEM compared to the FEM are consistent with the slope stability studies of numerous other authors The analysis results indicated that the FEM are greater F.S values than the LEM (Tantri & Lastiasih, 2015; Gallage et al., 2021) According to the construction feasibility of each countermeasure (N.C.Koei & JICA, 2007), as described in appendix slope cutting method is the good durability in some cases, easy to maintenance, good 91 construction ease, good construction cost, and good degree of safety The retaining method is the good durability in some cases, easy to maintenance, good construction ease in some cases, good construction cost, and good degree of safety An anchoring method is the very good durability, very easy to maintenance, good construction ease, and very good degree of safety but this method is a little higher cost than other methods Based on the analysis and construction feasibility, an anchoring method shows the effective countermeasure method for remedy solutions against landslide failure triggered by heavy rainfall and earthquake conditions h (a) (b) Figure 4.36 Summarize of F.S results under normal, rainfall, and earthquake conditions (a) LEM; (b) FEM (a) (b) Figure 4.37 Summarize of F.S results under normal, rainfall, and earthquake conditions (a) LEM; (b) FEM 92 CHAPTER CONCLUSIONS AND RECOMMENDATIONS 5.1 Conclusions This research focused on mechanism and countermeasures for deep-seated landslide in Lao Cai area This research performed the two objectives: 1) the simulation of slope stability by using numerical analysis of LEM (GEO-SLOPE) and FEM (PLAXIS); 2) Finding the effectiveness countermeasures for remedy solutions against landslide failure triggered by heavy rainfall and earthquake along the highway in Lao Cai province Based on the field investigation results, and numerical analysis results, and triggering factors was described to reveal the landslide mechanism with and without remedy solutions on slope The analysis results can contribute the appropriate slope stabilization methods to other similar landslide mainly in highway of mountainous regions The key conclusions can be drawn as following: For the 1st objective In the initial slope with and without rainfall and earthquake, the F.S values obtained h from LEM and FEM are less than the required value (F.S = 1.2) for rainfall condition and (F.S = 1.08) for earthquake condition, and the estimated failure surface occurs in the soil layer or above the bedrock layer, which indicates the instability of the slope and is consistent with the actual field results Hence, this study showed that the numerical analysis of both LEM and FEM model allow to predict the sliding surface of landslides based on the measured parameters of soil layers In addition, the F.S values from FEM are higher than that of LEM in both initial slope and remedy solution slope at normal, rainfall, and earthquake conditions because LEM and FEM are different theory and FEM program require to input the more detail parameters and no need the assumption of the slip surface range like LEM The advantages of both methods in LEM (e.g., computationally more efficient) and in FEM (e.g., theoretically more realistic and rigorous in terms of failure mechanism) This analysis pointed out that the analysis results from LEM (GEO-SLOPE) obtained only the F.S value, whereas the analysis results from FEM (PLAXIS 2D) obtained not only F.S but also displacement, anchor load, and other results Moreover, PLAXIS can model with more detailed input parameters such as the prestressed force in anchor system Thus, this study 93 demonstrated that FEM (PLAXIS) is more suitable for more complex cases and that practical work to design the slope stability works for accessing more information It can be concluded that the numerical analysis of LEM and FEM found out the mechanism of landslide due to the rainfall and earthquake conditions For the 2nd objective In this research, the heavy rainfall is the main triggering factor of two case studies This factor causing the reduction of the factor of safety against the slope stability Moreover, this study considered the effect of earthquake on slope to protect the future landslide Therefore, the effect of rainfall and earthquake on slope was analyzed to propose the remedy solutions against landslides A numerical analysis using the GEOSLOPE and PLAXIS 2D model was conducted to examine the sliding plane and the behavior of slope with three countermeasures The slope cutting method shows the sliding plane is still occur in soil layer and the F.S values are small results under rainfall and earthquake conditions The retaining method shows the sliding plane is above the retaining wall and the F.S values are greater than the required value according to the Vietnamese standard under rainfall and earthquake conditions An h anchoring method shows the sliding plane is very small surface and the F.S values are highest rather than retaining method under rainfall and earthquake conditions In the point of view construction feasibility, an anchoring method is suitable remedy solutions for long-term durability although a little higher cost than the other methods (N.C.Koei & JICA, 2007) as presented in appendix It can be concluded that an anchoring method is the effectiveness countermeasure for remedy solutions against landslide failure triggered by heavy rainfall and earthquake along the highway in Lao Cai province 5.2 Recommendations As of this research, some recommendations are as follows: - For the practical design of slope stabilization works, FE analysis (PLAXIS) should use to access the accurate results - If there is a steep slope, complex geology, a heavy rainfall area, and earthquake zone, saturated and unsaturated soil conditions should consider in rainfall-induced 94 slope stability model, and not only earthquake coefficient but also ground motion acceleration should apply in earthquake-induced slope stability model - When saturated/unsaturated soil condition consider, grain size distribution curve require to construct the rainfall infiltration model Thus, soil samples should take and laboratory testing should carry out to determine the value of unsaturated soil - When designing anchoring countermeasure method, the surface drainage systems to run-off the surface water and horizontal drainage pipes to reduce the ground water table should consider - For slope stabilization against deep-seated landslide under rainfall and earthquake conditions, the combination of ground anchor and soil nails method should select because this 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(b) 4th layer; (c) 5th layer 120 Passing (%) 100 80 60 40 20 0.001 0.01 0.1 10 100 Particle size (mm) Figure Grain size distribution curve of soil for case study of layer 100 SWCC and hydraulic conductivity of soil and rock layer in SEEP/W Figure Volumetric Water Content for soil and rock layer h Figure Hydraulic Conductivity for soil and rock layer Table Technical specification of applied countermeasures Type of countermeasure Anchor Parameter Unit ASTM A416-G270, 4T 12.7 mm Ultimate tensile force Soil nail Value Design force (Pre-load) Jacking force Material Diameter Yield strength 734.40 kN 290 kN 320 kN Steel SD 400 32 mm >400 N/mm2 101 Type of countermeasure Concrete beam frame Reinforced concrete wall Parameter Value Unit Ultimate tensile strength Concrete Concrete >560 N/mm2 M300 M300 Table Application of countermeasures for landslides (N.C.Koei & JICA, 2007) Type of work Durabilit y Maintena nce Construc tion Ease Constru ction Cost Degree of Safety Cutting Earthwork Surface Cover Water Drainage Vegetation Drainage ditches Horizontal drain holes Crib work h Slope Work Filling Rock Bolts Anchoring Walls and Resisting Structures Note: Ground Anchors Gabion Walls Retaining Walls = Very good or very easy, = Good or easy, = Good or easy in some cases 102 Model geometry of case study (Mong Sen) Initial Slope Remedy solution Remedy solution (Option 1) Remedy solution (Option 2) h Remedy solution 103 Model geometry of case study (Muong Hoa) Initial Slope Remedy solution Remedy solution Remedy solution h Details of countermeasure slope for case study (Mong Sen) (a) (b) 104 (c) (d) Figure Slope cross section with countermeasure for case study (Mong Sen): (a) remedy solution 1; (b) remedy solution (option 1); (c) remedy solution (option 2); (d) remedy solution Details of countermeasure slope for case study (Muong Hoa) h (a) (b) (c) Figure Slope cross section with countermeasure for case study (Mong Sen): (a) remedy solution 1; (b) remedy solution 2; (c) remedy solution 105