Questions and answers: design of surface excavations 327(b) Indicate, in general terms, the design changes required to
overcome any predicted instability probfems.
A78.7 A schematic section through the quarry face reveals that the
profile of the face is as below.
This indicates that, in general, sliding instability involving the entire
face will occur on features (either fracture planes for plane sliding or
lines of intersection of two planes for wedge sliding) that dip at an angle
that exceeds the angle of friction but is less than the face angle of 45".
Instability involving individual benches will occur for features that dip
at angles greater than 45" but less than 60".
If we assume that the fractures in the rock mass are cohesionless and
possess a friction angle of 35", then we can construct the following two
kinematic overlays for plane sliding and wedge sliding instability.