VIETNAM NATIONAL UNIVERSITY, HANOI VIETNAM JAPAN UNIVERSITY CHO THU THU NAING ROCKFALL MECHANISM AND COUNTERMEASURE FOR HOANG SA ROAD IN DA NANG CITY MASTER’S THESIS VIETNAM NATIONAL UNIVERSITY, HANOI VIETNAM JAPAN UNIVERSITY CHO THU THU NAING ROCKFALL MECHANISM AND COUNTERMEASURE FOR HOANG SA MAJOR: INFRASTRUCTURE ENGINEERING CODE: 8900201.04 QTD RESEARCH SUPERVISOR: Dr. NGUYEN CHAU LAN ROAD IN DA NANG CITY Hanoi, 2023 ABSTRACT The phenomenon of rockfall is a critical and dangerous case along the highway, especially in mountainous areas, that affects the traveler, vehicle, building, and other structures. As the infrastructure develops, more rockfall cases happen on the mountainous road. For this reason, modeling programs have become necessary for the decision-making process, such as protection and prevention against rockfalls, by simulating the behavior of rock failures, the stability of the slope, and remedial measures.
The thesis presents a study on rockfall behavior and mitigating the impacts of rockfall on the Hoang Sa road to the Son Tra Peninsula in Da Nang city. This study area has recorded rock collapse failure problems several times in the past. Especially significant rockfall events occurred three or four times along this highway last year. The retaining wall was damaged, and the tourism industry was delayed on the Hoang Sa road in Da Nang City due to the rockfall events.
The aim of the study is to solve the rockfall mitigation problem by selecting suitable remedial measures for preventing highway rockfalls on the Hoang Sa road. The study uses two types of numerical software: RocFall 2D and Plaxis 2D. RocFall software calculates rock trajectories, rock end-points, kinetic energy, velocity, and bounce height to examine the behavior of the rockfall process. Additionally, it determines a reliable remedial design in the passive method for the mitigation of rock slope failures.
On the other hand, Plaxis software calculates the prediction of the failure surface and factor of safety for slope stability. According to the field results, unstable blocks on the steep slope, highly fractured and cracked rock masses, as well as weathered rocks on the surface of granite rock, are factors that caused rockfall in the study area. The numerical model simulated the rockfall mechanism and rock slope stability analysis to find the suitable method for rockfall mitigation based on the 3 m3 of rock volume (8100 kg of rock mass) that fell from the steep granite slope surface. Based on each simulation result, the study concludes that the flexible barrier method and the anchored mesh method are the most feasible solutions for preventing future rockfall events on the Hoang road.
ACKNOWLEDGEMENTS My most sincere appreciation goes to my supervisor, Dr. Nguyen Chau Lan from the University of Transport and Communication. I am greatly indebted to him for his valuable advice and incredible support throughout my thesis period. I would like to say thank you to Prof.
Nguyen Dinh Duc (MCE Director). Moreover, my special thanks go to Prof. Hironori Kato (MCE co-director), Dr. Nguyen Tien Dung (MCE coordinator), Assoc.
Takeda Shinichi (MCE JICA expert), and Dr. Nguyen Ngoc Vinh (MCE lecturer) for their kind support, guidance, and recommendations during the lecture time and research period. I am grateful to the members of the JAIF scholarship organization as well as the rector of Vietnam-Japan University for providing me with the opportunity to gain valuable knowledge. I am thankful to the staff of the Master's Program in Civil Engineering for their support not only with course work via online learning but also with my thesis work.
Additionally, a very special thanks to the staff from (UTCGeo) for data collection and guidance on the thesis preparation. I am also thankful to my colleagues from MCE for their ideas and encouragement to successfully complete this work. I would like to extend further thanks to all individuals for their direct and indirect help. Finally, I am grateful for my family’s continued support for my graduate studies.
TABLE OF CONTENTS LIST OF TABLES. i LIST OF FIGURES .ii LIST OF ABBREVIATIONS. Background of the study. Location of the study area.
Statement of the problem. Scope of the study. The layout of the thesis. Outline of the thesis.
Structure of the thesis. Definition of rockfall. Causal mechanism of rockfall. Rock mass characteristics.
Computer programs to simulate rockfall. Rockfall mitigation methods and selection. Classification of countermeasures. Rock slope stabilization method.
Rockfall protection method. Case studies of rockfall events and mitigation measure. Overview of the study area. Past rockfall events in the study area.
Collection with field investigation. Collection with UAV, DEM model and GIS. Rockfall mechanisms analysis based on RocFall software. Rockfall mechanisms analysis without proposed method.
Rockfall mechanisms analysis with proposed method. Rock slope stability analysis based on Plaxis software. Slope stability analysis without proposed method. Slope stability analysis with proposed methods.
DATA ANALYSIS RESULTS AND DISCUSSIONS. Field data results. Field investigation results. UAV, DEM and GIS results.
Rockfall simulation results based on RocFall software. Simulation results of rockfall mechanisms without proposed method. Simulation results of rockfall mechanisms with proposed method. Rock slope stability simulation results based on Plaxis software.
Simulation results of slope stability without proposed method. Simulation results of slope stability with proposed methods. CONCLUSIONS AND RECOMMENDATIONS. 87 LIST OF TABLES Table 2.
Illustration of motion mechanism of falling rocks. Classification of countermeasures for rock falls. Overview of stabilization procedures. Overview of protection measures.
Annual and maximum rainfall data of Da Nang City. Input materials for RocFall. Input materials for initial condition of stone. Input parameters for granite.
Input parameters for granite calculated in the RocLab program. Input parameters for rainfall. Input parameters for retaining wall. Parameters of retaining components.
Input parameters for shotcrete. Input parameters for rock bolt. Rockfall mechanisms analysis result with varied rock mass. Proposed barrier design (option 1).
Proposed barrier design (option 2). Maximum total kinetic energy results without and with barrier .79 i LIST OF FIGURES Figure 1. Rockfall on the road connecting with the Ho Sau area in 2017 (Tuong Quan, 2021). Location map of study area.
Rockfall happened on the Hoang Sa road (a) April 2022; (b) May 2022; (c) August 2022. Past countermeasure design and current condition. A schematic slope profile of the rockfall process (Dorren, 2003). Motion pattern of falling rocks (N.
Schematic of rock slope collapse (N. Installation of structural shotcrete (Richard Andrew et al. Installation of an anchored Tecco mesh system in Northern California (Richard Andrew et al. Flexible barrier system (Qi et al.
Rockfall event in Badouzih, Keelung (Wei et al. Rockfall event in Badouzih, Keelung (Hancock, 2019). Rockfall on Sea to Sky highway (B.) (Volkwein et al. Rockfall case in Lai Chau province (News, 2018).
Rockfall case in Binh Dinh province (News, 2021). Hoang Sa road, Son Tra Peninsula (taken by using UAV investigation) 34 Figure 2. Rockfalls alongside a section of the road connecting with the Ho Sau area (NGUYEN DUC NAM, 2018). Rockfalls along a section of a road leading to the Ho Sau (Deep Hole) area (Landslide Warning Along Roads Leading to Son Tra Peninsula, 2020).
Rock rolled down onto the Hoang Sa road after a heavy rain in 2022 (Early Handling of Rockfalls on Son Tra Peninsula Taken, 2022. After rockfall conditions (VnExpress, 2022). Flow chart of overview of the study. Flow chart of the analysis study (1).
Flow chart of the analysis study (2). (a) UAV equipment; (b) Example of workflow in Agisoft Metashape to generate a DEM (González-Quiñones et al. Slope profile taken from google earth. Simulation model procedures for rockfall mechanisms analysis.
Model geometry without barrier method in RocFall for Son Tra area. The procedure for choosing the fallen stone location. Range of energy capacities for a variety of passive protection methods. Slope geometry with two proposed barrier options in RocFall software for Son Tra area.
The procedure for specifying the height and capacity of the barrier. Simulation model procedures for rock slope stability analysis. Monthly rainfall data in 2022. The model without proposed method for Plaxis (a) Ground water table; (b) Ground water and rainfall; (c) High water table; (d) High water table and rainfall 54 Figure 3.
The model with shotcrete method for Plaxis (a) Ground water table; (b) Ground water and rainfall; (c) High water table; (d) High water table and rainfall. The model with anchored mesh method for Plaxis (a) Ground water table; (b) Ground water and rainfall; (c) High water table; (d) High water table and rainfall. Survey result photos (May, 2022). Survey result photos (October, 2022).
(a) DEM model from UAV pictures; (b) Imaged of rocks with a high-risk of rockfall taken by UAV; (c) Serious rockfall location point taken from google earth. Overview of contour map in Son Tra Penninsula. Rock trajectories and end point results (a) Position of stone (1); (b) Position of stone (2); (c) Position of stone (3); (d) Position of stone (4); (e) Position of stone (5). Bounce height results with different fallen rock location.
Rockfall mechanisms analysis result without barrier method. Maximum total kinetic energy with varied rock mass. Bounce height results. Rock mechanism analysis results of barrier option 1 with 2000 kJ (a) 3 m barrier height; (b) 4 m barrier height; (c) 5 m barrier height; (d) 6 m barrier height.
Rock mechanism analysis results of barrier option 1 with 3000 kJ (a) 3 m barrier height; (b) 4 m barrier height; (c) 5 m barrier height; (d) 6 m barrier height. Rock mechanism analysis results of barrier option 2 with 2000 kJ (a) 3 m barrier height; (b) 4 m barrier height; (c) 5 m barrier height; (d) 6 m barrier height. Rock mechanism analysis results of barrier option 2 with 3000 kJ (a) 3 m barrier height; (b) 4 m barrier height; (c) 5 m barrier height; (d) 6 m barrier height. Failure surfaces corresponding to FOS values for existing condition.
Failure surfaces corresponding to FOS values under used shotcrete method. Failure surfaces corresponding to FOS values under used anchored mesh method. Comparison results (a) Barrier option 1; (b) Barrier option 2. Factor of safety results without or with reinforcement methods .81 iii LIST OF ABBREVIATIONS COR Coefficient of restitution D Disturbance factor DSM Digital Surface Model DEM Digital Elevation Model E Young’s modulus E Kinetic energy of falling rocks Ev Linear velocity energy of falling rocks Er Rolling energy of falling rocks EA1 Elastic axial stiffness EI Elastic bending stiffness FOS Factor of safety GSI Geological strength index GIS Geographic Information System H Falling height LMA Lumped mass approach m Mass unit of falling rocks mi Intact rock parameter Msf Strength reduction factor RBA Rigid body approach Rn Normal coefficient of restitution Rt Tangential coefficient of restitution RMR Rock mass rating Pmax The maximum impact force UAV Unmanned aerial vehicle w The unit weigh of the plate iv CHAPTER 1.
Background of the study Rockfall is one of the most common geohazard problems and the fastest type of landslide that happens mainly in mountainous regions. Compared to other slope instability failures, rockfall events happen more frequently. It is very dangerous for people who travel on the road at the toe of the steep terrain. Rockfalls with high energies and velocities can cause loss of life and significant damage to vehicles and infrastructure that are near or within the area of rockfall movement.
Rock slope failure cases occur not only in developed countries but also in developing countries. Most countries around the world have experienced rockfall hazards along the road in hilly regions.