Slope Stability Analysis

Ala N Aljorany/ IRAQ

Zhang Yaqing/ China

Summer Training Course for Slope Land

Disaster Reduction

Aug. (4th.-15th.), 2013

Hydrotech Research Institute

National Taiwan University

Content

• Introduction

• Types of Slopes

• Methods of Analysis

• Limit Equilibrium Methods

• Finite Element Method

• Sample Problem Definition

• Analysis By GEOSLOPE

• Analysis By PLAXIS

• Results and Discussions

• Conclusions

Introduction

• Geotechnical Engineer often faces the problem of

construction on sloping land or the stability of

Slopping land itself.

• The problem is simply, the tendency of sliding one

mass of soil on another slopping one or slopping

bedrock.

Slopping Land

Types of Slopes

• Man-made Slope.

• Natural Slope.

Some times can be classified

as:

- finite slope and

- infinite slopes.

The description of slope

depend on the lateral

dimension of the sloping

land and the thickness of

sliding mass.

Slope Stability Analysis

• The analysis of slope stability is mainly to define

the extent of stability of a certain slope.

• This can be expressed as Factor of Safety (FS):

• Mathematically, equals the resisting forces divided

by the driving forces, or the resisting moments

divided by the driving moment.

Methods of Analysis

There are two broad approaches to analyze the problem:

•Methods that based on the Limit Equilibrium approach.

•The Finite Element Method.

In the first approach, it is assumed that the sliding soil mass

will start to move once the shear stress on a certain plane

(surface) reaches its limiting value. The surface of sliding is

called (Slip Surface).

Infinite Slope

Finite Slope

Method of Slices

Statical Indeterminacy of the Problem

Different Slices Methods

- Ordinary or Swedish Circle (Fellenious)

Method, (Fellenious, 1936).

- Bishop’s Method, 1955.

- Spencer Method, 1967.

- Morgenstern- Price Method, 1965.

Sample Problem

1:10

2:1

1:5

1:10

Top Soil: γ= 18, φ= 33 Deg

c= 30kPa, υ=0.35.

Rock: γ= 22, φ= 48 Deg

c= 200kPa, υ=0.2

Geo-Slope Results

Results of PLAXIS 8.2

Conclusions

• The values factor of safety obtained by both

Geo-Slope and PLAXIS are almost identical.

• The shapes and locations of the most critical

slip surface obtained by both computer codes

are identical as well.

• When the top soil gets fully saturated, the

slope of the sample problem in hand becomes

no longer stable.

Thank You

for

Your Time