Civil Engineering Reference
In-Depth Information
Figure 6.7
A tension crack
behind a sliding rock mass in
which significant horizontal
displacement has occurred
(above Kooteney Lake, British
Columbia).
In summary, the presence of a tension crack
should be taken as an indication of potential
instability and that, in the case of an important
slope, this should signal the need for a detailed
investigation of stability.
surface, if it were to occur, would follow minor
geological features and, in some places, pass
through intact material, how can the inclination
of such a failure path be determined?
The first assumption that must be made con-
cerns the shape of the slide surface. In a weak
rock slope or a soil slope with a face angle less
than about 45
◦
, the slide surface would have a cir-
cular shape. The analysis of such a failure surface
is discussed in Chapter 8.
In steep rock slopes, the slide surface is approx-
imately planar and the inclination of such a plane
can be found by partial differentiation of equa-
tion (6.4) with respect to
ψ
p
and by equating the
6.3.4 Critical slide plane inclination
When a persistent discontinuity such as a bedding
plane exists in a slope and the inclination of this
discontinuity is such that it satisfies the conditions
for plane failure defined in Figure 6.2, stability of
the slope will be controlled by this feature. How-
ever, where no such feature exists and a sliding
