Engineering Rock Mechanics

322 Design and analysis of surface excavations

Upper angle limit:

90"

to slope dip, yi

boundary of failure criterion

Dip direction of slope

(b)

30" friction and 75" slope dip

Figure 18.9 Construction of instability overlay for flexural toppling.

construction is the same, the location of the overlay is different in the
two cases. This is because the discontinuities dip in the same direction as
the slope for plane instability, but into the slope for flexural toppling
instability.