Find the factor of safety:

Find the factor of safety against (a) sliding and (b) overturning for the dam section within Example 9.1 (coefficient of friction among soil and dam base is 0.6).

Solution

(a)        The vertical load is the weight (W) of the masonry dam which has been compute as 582.4 kN per metre of the wall

The frictional force at base is F = μ W

or        F = 0.6 × 582.4 kN = 349.44 kN

The sliding force is the horizontal pressure P = 281.25 kN.

Hence, the safety factory against sliding = 349.44/281.25 = 1.243

(b)       A moment of the vertical load W about the toe D is

W (b - x¯) = 582.4 (5 - 1.782) = 1874.16 kNm

which is the stabilizing moment.

The overturning moment because of water pressure is

P ⋅ h/3 = 281.25 × 2.5 = 703.125 kNm

∴ The factor of safety against overturning = 1874.16/703.125 = 2.67 .