Environmental Engineering Reference
In-Depth Information
Figure 2.28.
Typical conditions likely to result in landsliding of slope in weathered granite (based on
Patton & Hendron, 1973).
Deere and Patton (1971) describe weathering profiles developed in most common rock
types and show how landsliding often occurs within them.
Many valleys (particularly in Europe and North America) have been subjected to
glaciation, in relatively recent geological times (see Section 3.12). The resulting deepening
and steepening has in some cases contributed to rockfills and landslides.
There are many different forms and mechanisms of landsliding and it is beyond the
scope of this topic to describe them. For useful accounts readers are referred to Turner
and Schuster (1996), Varnes (1958, 1978), Selby (1982), Hunt (1984) and Hutchinson
(1988). Stapledon (1995) provides some guidelines for geological modelling of landslides,
and examples of their application.
2.10.1
First-time and “reactivated” slides
A distinction can be made between “first-time” landslide activity which develops at “intact”
sites like that shown on Figure 2.28, and that which is simply reactivation or increased activ-
ity of an old landslipped mass which has become stabilised or is subject to only small occa-
sionally active movements.
This distinction is important because there is a very large difference between the pre-
dictability and characteristics of the two kinds of sliding.
2.10.1.1
Reactivated slides
ICOLD (2002) has shown that in at least 75 percent of cases, disturbance of an old inac-
tive or occasionally active landslide e.g. by cutting into or inundating its toe, causes reac-
tivation or increased rates of movement. Hence if there is clear evidence that all or part of
a slope is an old slide mass, a high risk of reactivation by construction activities or reser-
voir operation must be assumed, at least until geotechnical conditions in the slope are suf-
ficiently well known to prove otherwise.
