Volume 6 – Geotechnical Manual, Site Investigation and Engineering ...

Chapter 6 SLOPE STABILITY
APPENDIX 6.A
WORKED EXAMPLE: SLOPE STABILITY
A.1 Problem
The worked example presented herein illustrates the application of stability analysis by way of
the Fellenius method of slices to determine the factor of safety in terms of effective stresses.
The related slope configuration is shown in Figure 6.13 below.
Figure 6.13 Related Slope Configuration
The applicable soil properties and strength parameters are given as follows:
i.
ii.
iii.
iv.
Soil unit weight (above & below water table), γs
Effective cohesion, c’
Effective angle of shearing resistance, φ’
The soil mass is divided into slices of 1.5m wide sing the
expression below (Eqn. 3.1), the resulting factor of
safety is established as follows.
= 20 kN/m 3
= 10 kN/m 2
= 29°
F = c'L a+tan' ∑Wcosα-ul
∑ Wsinα
(6.3)
Solution:
i. The weight of each slice, W = γsbh
= 20 x 1.5 x h
= 30h kN/m
March 2009 6A-1