Stability of Rock Wedges and Excavation Surfaces - Rock Mechanics Based on an Anisotropic Jointed Rock Model - page 305

er). For stability, the limit equilibrium at the external and internal failure lines of each
block must be fulfilled ( μ GWM = 1). Otherwise, an additional force is required to stabilize

the wedge. If this force is a driving force the utilization factor

μ GWM is less than 1 and

the wedge is stable. If this force is a resisting force μ GWM is greater than 1 and the wedge

needs to be supported by an anchor force. The internal and, if required, also the external
failure lines are varied in order to find out the most unfavorable configuration of blocks
leading to the maximum utilization factor.

Figure 11.15 Simplified analysis methods for the stability of two-dimensional rock wedges against
sliding on polygonal surfaces

Since in the general wedge method a shear resistance along the internal failure lines
is accounted for, this method leads to less conservative results compared with Janbu's
method (

μ GWM < μ J ).