Calculation of the daylight envelope for plane failure of rock slopes

Plane failure—the downdip sliding on a single set of discontinuities—constitutes an important mode of failure of rock slopes. In assessing the potential for such failure, the orientation of the discontinuities relative to that of the face of the slope is a crucial consideration. Discontinuities that dip in towards the face cannot act as sliding surfaces because movement is prevented by the lack of space for the displaced mass (Fig. 1(a)). On the other hand, discontinuities that dip generally in the direction of the rock face are kinematically viable: such planes of weakness are said to daylight.

It...