Stability Analysis of Slope Based on FLAC3D Using Strength Reduction Method. Speaker: Tran, Thi Kim Tu Advisor: Chuen Fa Ni Date: 2017/03/02

Transcription

1 Stability Analysis of Slope Based on FLAC3D Using Strength Reduction Method Speaker: Tran, Thi Kim Tu Advisor: Chuen Fa Ni Date: 2017/03/02

2 1. INTRODUCTION 2. METHODOLOGY 3. RESULTS AND DISCUSSION 4. CONCLUSION 5. FUTURE WORKS 2

3 INTRODUCTION 2D simulation by Geoslope software based on Finite element method Solve a weak form of the governing equation on an unstructured mesh 2D simulation of slope by FLAC based on Finite difference method Solve a strong form, often on a structure grid Zienkiewicz and Taylor 1898; Gharti et al. 2012) The FEM or FEM combined with other methods has been widely applied to 3D slope stability analysis (Stolle and Guo 2008; Li et al. 2009, 2010; Stianson et al. 2011; Gjarti et al. 2012) whereas the FDM has been relatively less (Chung 2003; Wei et al. 2009) 3

4 Literature Review INTRODUCTION 1. Simulation analysis on three-dimensional slope failure under different conditions (Zhang Ke, Liu Zi-yao 2011) 2. Slope stability analysis by strength reduction (Dawson, E.M., Roth, W.H., and Drescher, A. 1999) 3. On the boundary condition in slope stability analysis (Ashok K. Chugh 2003) 4

5 Motivation INTRODUCTION Including experiment - numerical modeling interactions. To understand clearly the behaviours of a sandy slope under different conditions. These results can be used directly to offer suggestions for landslide hazard preparedness or safe and economical design of infrastructure such as excavations, embankments.. 5

6 Overview FLAC3D 2. METHODOLOGY FLAC3D (Fast Lagrangian Analysis of Continua in 3 Dimensions) A numerical modeling code for advanced geotechnical analysis of soil, rock, and structural support in three dimensions. FLAC3D solves the full dynamic equations of motion FLAC3D contains an embedded language, FISH, that gives the user access to all internal variables and allows custom-written functions. 6

7 2. METHODOLOGY Simulation Simple Slope Complex Slope Model setup 1. Generate grid, deform to desired shape 2. Define material properties 3. Specify boundary and initial conditions Step to equilibrium state Examine the model response AutoCad 2007.DXF (2D) FLAC3D 7

8 Model setup Examine the model response Model test needed Result unsatisfactory Result satisfactory Alteration (change boundary condition) Step to solution 2. METHODOLOGY Model makes sense Examine the model response Yes Parameter study needed No End 8

9 2. METHODOLOGY Factor of safety (FOS) and strength reduction technique FOS is the ratio of the available strength of soil material to that required to maintain equilibrium The current approach uses a shear strength reduction technique in which reduced shear strength parameter c ' and ' c c ' ' arctan SRF ' tan SRF Griffiths and Lane (1999), Wet et al (2009), Zheng et al (2009).. 9

10 2. METHODOLOGY Boundary condition The choice of appropriate boundary conditions is important for 3D slope stability analysis. For the end faces: Condition 1: fixing the y direction displacement (v=0) Condition 2: fixing the (x, y) direction displacement (u=v=0) Condition 3: fixing the (x, y, z) direction displacement (u=v=w=0) 10

11 Mesh form and mesh size The results from FDM with the strength reduction technique are sensitive to the design of the mesh (Shukha and Baker 2003) To choose an appropriate mesh model, 2. METHODOLOGY 2 popular types of mesh form: hexahedra tetrahedral 3 mesh sizes: coarse optimized fine 11

12 RESULTS AND DISCUSSION Example factor of safety calculations using the strength reduction method Slope model geometry 12

13 RESULTS AND DISCUSSION Example factor of safety calculations using the strength reduction method Factor of safety results The failure state calculated by FLAC3D is global minimum stability state Local and global minima by LEM (Chang et al. 2007) The location of the failure surface for the local minimum is very close to that from the SRM, and the failure surface for the global minimum from the LEM is not the critical failure surface from the SRM. 13

14 Slope model mesh with the real size RESULTS AND DISCUSSION 14

15 Model in FLAC3D RESULTS AND DISCUSSION

16 CONCLUSION 3D analysis could offer a reflection on the actual state of slope. The hexahedral mesh form chosen in the present study and the mesh size is fine (as much as possible) as long as the elapsed time is acceptable. Collect data for the study and develop conceptual model for numerical modeling.. 16

17 FUTURE WORKS Experiment Determine the hydraulic conductivity in laboratory 1. The hydraulic conductivity of saturated soils 2. The hydraulic conductivity of unsaturated soils Develop conceptual model for numerical modeling. 17

18 THANK YOU FOR YOUR ATTENTION! 18