Speaker: Tran, Thi Kim Tu

Advisor: Chuen Fa Ni

Date: 2017/03/02

Stability Analysis of Slope Based on

FLAC3D Using Strength Reduction

Method

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1. INTRODUCTION

4. CONCLUSION

3. RESULTS AND DISCUSSION

2. METHODOLOGY

5. FUTURE WORKS

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INTRODUCTION

2D simulation by Geoslope software based on

Finite element method2D simulation of slope by FLAC

based on Finite difference method

Solve a weak form of the governing

equation on an unstructured meshSolve 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)

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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)

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MotivationINTRODUCTION

• 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..

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FLAC3D (Fast Lagrangian Analysis of Continua in 3 Dimensions)

2. METHODOLOGY

A numerical modeling code for advanced geotechnical analysis of

soil, rock, and structural support in three dimensions.

FLAC3D contains an embedded language, FISH, that gives the user

access to all internal variables and allows custom-written functions.

FLAC3D solves the full dynamic equations of motion

Overview FLAC3D

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.DXF (2D)

FLAC3D

AutoCad 2007

Simulation

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

2. METHODOLOGY

Simple Slope Complex Slope

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2. METHODOLOGY

Result unsatisfactory

Examine the model response Result satisfactory

Model makes sense

Alteration

(change boundary

condition)

Step to solution

Examine the model response

Model test needed

Parameter study needed

No

End

Model setup

Yes

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Factor of safety (FOS) and strength reduction technique

The current approach uses a shear strength reduction technique in which

reduced shear strength parameter and 'c '

tan' ' arctan

'

cc

SRF SRF

FOS is the ratio of the available strength of soil material to that required to

maintain equilibrium

Griffiths and Lane (1999), Wet et al (2009), Zheng et al (2009)..

2. METHODOLOGY

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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)

2. METHODOLOGY

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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)

3 mesh

sizes:

coarse

optimized

fine

2 popular types of mesh

form:

hexahedra

tetrahedral

To choose an appropriate mesh model,

2. METHODOLOGY

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RESULTS AND DISCUSSION

Example factor of safety calculations using the strength reduction method

Slope model geometry

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RESULTS AND DISCUSSION

Example factor of safety calculations using the strength reduction method

Factor of safety resultsLocal and global minima by LEM

(Chang et al. 2007)The failure state calculated by

FLAC3D is global minimum stability

state

The location of the failure surface for the local minimum 1.3848 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.

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RESULTS AND DISCUSSION

Slope model mesh with the real size

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RESULTS AND DISCUSSION

Model in FLAC3D

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2

3

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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.

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FUTURE WORKS

1. The hydraulic conductivity of saturated soils

2. The hydraulic conductivity of unsaturated soils

Experiment

Determine the hydraulic conductivity in laboratory

Develop conceptual model for numerical modeling.

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THANK YOU FOR YOUR ATTENTION !