Engineering Geology

E n g i n e e r i n g G e o l o g y
at a particular time, whereas others provide an indication of the possibility of landslide occurrence
(Fig. 8.8). The latter are landslide susceptibility maps and involve some estimation of
relative risk (Van Westen et al., 2003).
Effective landslide hazard management has done much to reduce economic and social losses
due to slope failure by avoiding the hazards or by reducing the damage potential (Schuster,
1992). This has been accomplished by prohibition, restrictions or regulations placed on development
in landslide-prone areas; application of excavation grading, landscaping and construction
codes; use of remedial measures to prevent or control slope failures; and landslide warning systems.
These measures may be used in a variety of combinations to help solve both existing and
potential landslide problems. They are generally applicable to flows, slides and falls. Recurrent
damage from landslides can be avoided by permanently evacuating areas that continue to experience
slope failures. Structures may be removed or converted to a use that is less vulnerable to
landslide damage. Various types of land-use and land-development regulations can be used to
reduce landslide hazards. They are often the most economical and most effective means available
to a local government. Landslide-prone areas can be used as open spaces or the density
of development can be kept to a minimum to reduce the potential for damage. Zoning and subdivision
regulations, as well as moratoriums on rebuilding, can be used to meet these objectives.
As the same preventative or corrective work cannot always be applied to different types of
slides, it is important to identify the type of slide that is likely to take place or that has taken
place. Also, it is important to bear in mind that landslides may change in character and that
they are usually complex. When it comes to the correction of a landslide, as opposed to its
prevention, since the limits and extent of the slide are generally well defined, the seriousness
of the problem can be assessed. In such instances, consideration must be given to the stability
of the area immediately adjoining the slide. Obviously, any corrective treatment must not
adversely affect the stability of the area about the slide.
If landslides are to be prevented, then areas of potential landsliding must be identified, as
must their type and possible amount of movement. Then, if the hazard is sufficiently real, the
engineer can devise a method of preventative treatment. Economic considerations, however,
cannot be disregarded. In this respect, it is seldom economical to design cut slopes sufficiently
flat to preclude the possibility of landslides.
Landslide prevention may be brought about by reducing the activating forces, by increasing
the forces resisting movement or by avoiding or eliminating the slide. Reduction of the
activating forces can be accomplished by removing material from that part of the slide that
provides the force that will give rise to movement. Complete excavation of potentially unstable
material from a slope may be feasible; however, there is an upper limit to the amount of material
that can be removed economically. Although partial removal is suitable for dealing with
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