Stability of Rock Wedges and Excavation Surfaces - Rock Mechanics Based on an Anisotropic Jointed Rock Model - page 300

where are the components of G, P and W normal and
parallel to set D1 that are calculated in terms of > 1, the wedge needs to be

supported by an anchor force that can be determined in a corresponding manner as
described above by replacing by

β D1 . If μ

.

Figure 11.11 Two-dimensional rock wedge supported by a stepped surface (Kovari & Fritz 1984)

Sliding on a polygonal surface
In a rock mass with two or more discontinuity sets sliding may take place along a poly-
gonal surface (Fig. 11.12). However, for a monolithic failure body only a circular or
linear failure line is kinematically admissible (Gussmann et al. 2002). Sliding on a polyg-
onal surface therefore involves failure within the sliding rock mass forming rock blocks
as illustrated in Fig. 11.12.

The individual blocks are supported by so-called “external failure lines” formed by dis-
continuities and laterally bounded by so-called “internal failure lines” (Fig. 11.13). The
latter may be formed in the intact rock or along planes of weakness such as discontinuities.
Kovari & Fritz (1978) formulated the sliding stability of two-dimensional rock wedges
supported by polygonal surfaces according to the concept of global safety considering
n blocks that are supported by n external failure lines and separated by n - 1 internal
failure lines. In the following, a corresponding formulation according to the partial safe-
ty factor method is presented.