Environmental Engineering Reference
In-Depth Information
Scarp
Failure surface
Original surface
Slumped mass
(a)
(b)
Scarp
Failure
surface
Rock debris
(c)
FIGURE 9.2
Slide forms in rock masses. (a) Rotational slide failed
through joints and weak basal horizontal bed.
(b) Translational sliding of blocks along a weak planar
surface such as shale. (c) Planar slide failed along steeply
dipping beds after cutting along lower slope. (d) Wedge
failure scar. Failure occurred along intersecting joints and
bedding planes when cut was made in obliquely dipping
beds (see
Sections 9.2.3
and
9.2.4).
(d)
rotational slides (
Table 9.2)
.
Planar slides in rock masses commonly reach veloc-
ities of 10 to 50 m/h (Banks and Strohn, 1974). Large planar slides in rock masses
can achieve tremendous velocities, at times of the order of 200 m/h, as has been
computed for the Vaiont slide (see Section 9.2.3). Habib (1975) considers these
high velocities to be the result of movement of the rock mass over a cushion of
water that negates all frictional resistance. The cushion is caused by heat, gener-
ated by shearing forces, which vaporizes the pore water. Such velocities are the
major reason for the often disastrous effects of planar rock slides. Slide failures
are usually progressive, and can develop into failure by lateral spreading, as well
as into avalanches and flows.
