Stability of Slopes - Elements of Soil Mechanics - page 393

Fig. 13.9 Tension crack in a cohesive soil.

Example 13.2: Factor of safety against sliding

Figure 13.10 gives details of an embankment to be made of cohesive soil with c u = 20 kPa.
The unit weight of the soil is 19 kN/m 3 .
For the trial circle shown, determine the factor of safety against sliding soon after
construction. The weight of the sliding sector is 329 kN acting at an eccentricity of
4.8 m from the centre of rotation. What would the factor of safety be if the shaded
portion of the embankment were removed? In both cases assume that no tension crack
develops.

Solution:

Disturbing moment = 329 4 8 × . = 1579 kN m

71
180

Restoring moment = c R

2

θ = × × 20 9

2

× = π 2007 kN m

u

2007
1579

⇒ = F = 1 27 .

Fig. 13.10 Example 13.2.