Effect Of A Weak Layer In Slope Stability

The objective of this paper is to present a practical method for calculating minimum safety factors of rock slopes with a horizontal layer of weak material. It is demonstrated that the most critical failure surface, in this case, is a bilinear surface composed of a horizontal failure surface inside the weak layer and an inclined surface inside the rock. The model presented in this paper shows that with a good approximation, the change in slope for the bilinear failure surface may occur directly below the slope crest. This assumption simplifies the calculation of safety factors considerably, because the most critical failure surface is located directly, and the trial computations for a number of failure surfaces are not necessary. Special parameters involved in slope stability analyses of highwalls in open-pit mines are discussed and, by an example calculation, the applicability of this method is demonstrated.