Kinematic analysis for sliding failure of multi-faced rock slopes

Abstract

Most kinematic analyses for rock slope stability have dealt with single-faced slopes (SFS) with a planar surface of a constant strike. However, there are many slopes with non-planar surfaces along road cuts and in open pits, etc. Multi-faced slopes (MFS) consist of two or more faces with different strikes. Multi-faced slopes have different sliding conditions compared to single-faced slopes because of their geometrical characteristics, i.e. convex surface on plan view. On stereographic projection, a sliding envelope of a multi-faced slope is a union of envelopes of individual faces formed on the slope surface. Sliding modes of multi-faced slopes are divided into two types and they are subdivided into two modes, respectively; Type 1 single or double plane sliding and Type 2 single or double plane sliding. Type 1 sliding failures are controlled by the same rule as the single-faced slopes as suggested by Hocking [Int. J. Rock Mech. Min. Sci. Geomech. Abstr. 13 (1976) 225]. Type 2 sliding failures can occur on multi-faced slopes only. A Type 2 sliding block must have two or more adjacent slope faces. Though two joint sets must be developed for Type 1 sliding, Type 2 single plane sliding can occur with only one joint plane in the multi-faced slopes. A simple Type 2 single sliding block is composed of one joint plane, two slope faces and the upper natural slope surface. If two joint planes act as sliding planes for plane failures at two adjacent faces of a multi-faced slope, they form a block of Type 2 double plane sliding in the slope. On a stereographic projection, a Type 2 sliding zone is defined as the area between the true dip lines of two side-slope faces in the sliding envelope of a multi-faced slope. If the true dip lines of one or two joint planes plot within a Type 2 sliding zone, Type 2 sliding failure can be possible.