326 Design of surface excavations
For each of the azimuth values under consideration, we identdy
the maximum slope angle that will avoid instability for this particular
mechanism, and then tabulate the results, as shown below.
Slope dip direction Maximum slope angle Critical angle critical mode
flexural toppling all modes
000
015
030
045
060
075
090
105
120
135
150
165
180
195
210
225
240
255
270
285
300
315
330
345
90
90
90
90
90
90
90
90
55
90
90
90
90
90
90
40
40
90
90
90
90
80
80
8055
57
63
70
65
52
45
38
35
35
35
35
47
57
75
40
40
87
75
65
60
57
53
52wedge
wedge
wedge
wedge
wedge
wedge
wedge
wedge
wedge
plane
plane
plane
wedge
wedge
wedge
flexural toppling
flexural toppling
wedge
wedge
plane
wedge
wedge
wedge
wedgeAll angles in degrees.
We see that flexural toppling does indeed become a dominant po-
tential failure mode at two of the azimuth orientations, namely 225"
and 240".418.7 A trial design for a proposed 100 m deep roadstone quarry
can be approximated in plan by a circle. The quarry has been
designed with a number of 10 m high benches, such that the overall
slope angle is 45O and the individual bench angles are 60°.
Preliminary mapping of the site has established that the rock
mass contains four dominant sets of fractures, having the following
mean Orientations:
Feature Gavage Joint set A Joint set B Bedding
Dip 36O 75O 45O 280
Dip direction 01 5O 330° oaoo 260°(a) Using kinematic feasibility techniques, determine whether or
not conditions exist that could lead to instability in the proposed
slopes.