Geology Reference
In-Depth Information
Monitoring can be conducted in the real time, for example, using
total systems that record movements at short intervals automatically
or vibrating wire strain gauges with data transferred to the respon-
sible person, as discussed in
Chapter 4.
Alternatively, periodic
examinations using inclinometers, radar or photogrammetry can
all be effective.
Very large rock slope failures often involve some zones where
sliding on discontinuities is happening whilst elsewhere the rock
mass may be acting as an isotropic fractured mass in a Hoek-
Brown way and in other areas intact rock may be failing.
Explaining such complex failures is a much easier task than pre-
diction. Many large failures have been studied in detail, and these
cases are probably the best place to look for ideas and inspiration
when dealing with large slopes (e.g. Bisci
et al
., 1996; Eberhardt
et al
., 2004).
For soil slopes, where the ground mass can be regarded as essen-
tially isotropic within each unit or layer (stratum), analysis
involves searching through the slope geometry, looking for the
potential slip planes with the lowest FoS. This can be done
easily using available software such as SLOPE-W and Slide. In
weathered rock and indeed many soils, stability might well be
controlled by adverse relict joints and other weak discontinuities
so that a variety of possible failure modes need to be addressed.
An example of hazard models requiring particular analysis within
cut slopes in Eocene mudstone at Po Chang in Korea is given in
The slope shown in
Figure B6-5.1
is within a development site near Po Chang, South Korea. The rock
comprises weak to strong bedded mudstone containing strong rounded concretions. The slope was
excavated several years prior to the photograph and in some areas is deteriorating very rapidly, with
large screes of disintegrated mudstone debris.
Apart from bedding, the main discontinuities are orthogonal vertical sets of joints, probably
formed during burial. There are also conjugate shear fractures, inclined at steep angles. As
Figure
B6-5.2
shows, the same rock is exposed in unprotected slopes adjacent to main roads on the
outskirts of Po Chang. There are evident recent failure scars in some of the slopes.
This case provides an example of how a single slope or series of slopes may contribute several
different hazards, each of which needs to be considered in a different way, as illustrated in
Figure
