Department of Civil Engineering

Indian Institute of Technology Madras

CE 3350 Geotechnical Engineering

August – December 2012

Stability Analysis of Slopes

1. Taylor (1937) had published charts for determining the minimum factor of safety of

homogeneous slopes based on total stress analysis (=0). The stability number Ns is

defined as Ns=Cuu/FH in which Cuu is the undrained cohesive strength of soil, F is the

factor of safety, is the unit weight and H is the height of slope. Ns is obtained from

charts as a function of slope angle () and the depth factor (D).

Use this chart to determine the factor of safety for the following two cases:

a. H = 10 m, =40, Cuu=50 kPa, =20 kN/m3, Depth factor, D=1.5

b. H = 10 m, =60, Cuu=50 kPa, =20 kN/m3, Depth factor, D=1.5

2. A soil slope carrying uniform surcharge of 35 kPa (corresponding to the pressure

exerted by typical highway as per IRC guidelines) is shown in Figure-2. One possible

slip circle is shown in the figure.

Determine the factor of safety of the slope using Ordinary Method of Slices (OMS).

The surcharge pressure acting on the slope may be considered by increasing the

weight of the slice (per unit length of slope).

3. What is the effect of shallow-height berms on the factor of safety on high

embankments resting on soft ground. Assumed deep seated failure. Clearly write

your technical reasoning with neat sketches.

4. Briefly describe how to identify a slope at the verge of failure (due to deep seated

failure) during site investigation. Also describe some of the short term and long term

remedial measures that you may take as a geotechnical engineer.

Slope soil:

C=20 kPa, =30, =20 kN/m3

Foundation soil:

C=50 kPa, =0; =18 kN/m3

H=10m

6 m

(Figure is not to scale)

radius of slip circle = 20 m

X=7.5 m

L=15 m