Stability of Retaining Walls:

Sliding

As retaining walls are subjected to horizontal (as well as vertical loads) there will be a tendency of the wall to move or slide in the direction of the force. This is resisted by the frictional force acting at the base of the wall. If the coefficient of friction between the base and the soil is μ and W is the total vertical forces, then as the vertical reaction R = W, the frictional force

F = μ R = μ W.

Hence, for a condition of no sliding, total horizontal forces

P_h < μ W

FS = μW /P_h                                                                                                                                                 

The ratio μW/P_h is known as the factor of safety against sliding, and it should never be less than 1.0. Normally the factor of safety against sliding is taken as 2.0.