Engineering Rock Mechanics

Questions and answers: design of surface excavations^323

excavation required for this slope is
given by H2/2 tan $ per unit length of
slope crest.
Thus, to sketch the quarry we can
draw a circle of some convenient dia-
meter to represent the quarry floor, and
then mark a radial distance outwards
from this at each of the azimuths in the
stability tables, such that the distance
is proportional to 1/ tan$. Connecting the points thus marked will give
an approximation to the crest of the slope. In order to determine the
optimal trend for the access road, we simply use the equation above to
compute the area of excavation required for the two side slopes, and
choose the direction for which this is a minimum. The result of these
calculations is given in the table below, together with a sketch of the
slope crest around a circular quarry.

k

Hltan ly

4

Slopedipdirection 000 015 030 045 060 075 090 105 120 135 150 165

Slopeangle, 1cI. 55 57 63 70 65 52 45 38 35 35 35 35

l/WlCI) 0.70 0.65 0.51 0.36 0.47 0.78 1.00 1.28 1.43 1.43 1.43 1.43

1/2 rn(1cI.I 0.35 0.32 0.25 0.18 0.23 0.39 0.50 0.64 0.71 0.71 0.71 0.71

Slopedipdirection 180 195 210 225 240 255 270 285 300 315 330 345

Slope angle 47 57 75 90 90 87 75 65 60 57 53 52

1/W*) 0.93 0.65 0.27 0.00 0.00 0.05 0.27 0.47 0.58 0.65 0.75 0.78

1/2W@) 0.47 0.32 0.13 0.00 0.00 0.03 0.13 0.23 0.29 0.32 0.38 0.39

Opposingslope 000, 015, 030, 045, 060, 075, 090, 105, 120, 135, 150, 165,

dipdirections 180 195 210 225 240 255 270 285 300 315 330 345

Combinedexca- 0.82 0.65 0.39 0.18 0.23 0.42 0.63 0.87 1.00 1.04 1.09 1.10

vation volume

I accessroad .\,