322 Design of surface excavations
sliding, wedge sliding and direct toppling. The maximum slope angles
are given in the following table.
Slope dip direction Maximum slope angle Critical angle Critical mode
plane wedge
000 15 10 10 wedge
015 15 13 13 wedge
030 15 13 13 wedge
045 75 12 12 wedge
060 75 10 10 wedge
075 90 8 8 wedge
090 90 10 10 wedge
105 90 11 11 wedge
120 90 12 12 wedge
135 38 20 20 wedge
150 38 35 35 wedge
165 38 28 28 wedge
180 90 24 24 wedge
195 90 22 22 wedge
210 90 20 20 wedge
225 90 20 20 wedge
240 90 22 22 wedge(^255 90 23 23) wedge
270 90 15 15 wedge
285 65 12 12 wedge
300 65 10 10 wedge
315 90 9 9 wedge
330 90 8 8 wedge
345 90 9 9 wedge
All angles in degrees.
Again, toppling instability is found to be unimportant. However, what
is clear now is just how troublesome wedge instability has become. We
find that, over the entire range of azimuths, wedge instability is the critical
mode, and that avoiding it drives the slope angle down to very low values.
418.5 Use the results from 418.3 to draw a plan of the slope crest
around the quarry excavation assuming that the floor of the quarry
is circular. Determine the best orientation for a rudiul access road
to the quarry floor (assume that the road can be constructed in any
direction and that the optimal orientation is for a road with the
steepest possible side slopes - so that excavation associated with
the road is minimized).
Repeat part (b) for an unknown friction angle, as was the case in
Q18.4.
A78.5 If we assume that the walls of the quarry are of uniform height
H, then the horizontal distance from the crest of the slope to the toe is
given by H/ tan @, where @ is the slope angle. In addition, the volume of