Civil Engineering Reference
In-Depth Information
N
1.5
2.4
.8
5
.3
.4
.5
1.0
3
.3
2
.5
4
1
1
5
4
3
2
>5
Notes:
a. Black triangles mark most likely position of poles of five sets
of discontinuities present in rock mass.
b. Shaded area surrounding pole position defines extent of
scatter in measurements.
c. Factors of safety for each combination of discontinuities are
shown in circle over corresponding intersection of great circles.
d. Dashed line surrounds area of potential instability (FS < 2).
Figure 7.16
Stereoplot of geological
data for the preliminary design of
highway slopes.
analysis can be carried out to determine the bolt-
ing force required to increase the factor of safety
to an acceptable level.
The stereoplot in Figure 7.17(a) can be used to
find the maximum safe slope angle for the slopes
of any dip direction. This stereographic analysis
involves positioning the great circle representing
the slope face for a particular dip direction in
such a way that the unstable region (shaded)
is avoided. The maximum safe slope angles are
marked around the perimeter of this figure and
their positions correspond to the orientation of
the slope face (Figure 7.17(a)). For example, if a
through-cut for a highway is planned in this rock,
the slope on the south side of the cut would be an
angle of 30
◦
and the slope on the north side would
be at 85
◦
(Figure 7.17(b)).
7.6 Comprehensive wedge analysis
7.6.1 Data for comprehensive analysis
If the friction-only wedge stability charts show
that the factor of safety is less than 2.0, then a
comprehensive stability analysis may be required
to calculate, for example, the bolting force to
achieve a required factor of safety. This analysis
takes into account the dimensions and shape of
