Geoscience Reference
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for steep-land farmers for whom non-use and relocation are not viable options. If
physical landslide models are to contribute to slope stabilization in tropical,
agricultural watersheds, then a driving cause for instability must be identi
ed, along
with the probability that a slope will fail. Importance of causal information is borne
out by physical slope-stability models that do consider the influence of dynamic
hydrology and plant growth. These models are computationally intensive and, to
our knowledge, have only been applied to engineered or
slope
formations (Duncan 1996; Collison et al. 1995; Anderson et al. 1990 ). Nonetheless,
results of these modeling exercises are relevant to
characteristic
field-level management. Collison
et al. (1995) found that planting trees on an engineered embankment only enhances
the embankment
is stability if soil hydraulic conductivity is relatively high. For
deep-soiled embankments with low hydraulic conductivity, planting trees was, in
fact, detrimental to stability. Macro-pore flow along tree roots increased perme-
ability, leading to elevated pore pressures in and below the rooting zone, while roots
themselves did not penetrate deeply enough to anchor against deep-seated slope
failure. Under such conditions, it is preferable to vegetate the embankment with
grass, or some similar shallow-rooted ground cover, that sheds water off the
saturated portion of the slope. Water management can be more important than
physical reinforcement for weathered and frequently saturated soils. Drainage
ditches, or water-shedding ground cover, may offer better slope stabilization than
trees. Information on the soils and hydrology of a landslide-prone area is therefore
necessary for the development of appropriate management recommendations;
simply reporting the probability of failure is not enough (Collison et al. 1995).
Landslide mitigation and control measures depend on detailed investigations,
including identifying of the causative factors (Bhandari 1988). The landslide
mitigation work can be broadly classi
'
ed into two categories: control work and
restriant work (Valdiya 2006). The control works involve modi
cation of the
natural conditions such as topography, geology, ground water, and other conditions,
that indirectly promote landslide. Restraint works cover construction of structure
such as surface and sub-surface drainage works, removal of earth from the unstable
area, and building buttress walls, piles, anchors, and retaining walls. Montgomery
(1986) and Valdiya ( 1987 ) have suggested four-fold strategy of the control of
landslides. This includes—(i)
(i) reduction of the slope angle and placement of addi-
tional supporting material at the foot of the slope; (ii) reduction of the load on the
slope by removing the rock or soil situated high up on the slope; (iii) the utilization
of retention structure; and (iv) removal of fluid by various kind of drainage systems.
Vegetation is being widely used for erosion control, to achieve slope stabilization
along the transportation routes in countries like Japan, Korea and Hong Kong. The
new technique for slope stabilization with the help of vegetation has been adopted
by the Korean Highway Corporation (Sung-Hwan Kim et al. 1997 ). A list of shrubs
and trees that are useful for slope stabilization is given by Gupta ( 1979 ). Vegetation
tur
ng is the most effective and important corrective measures, particularly for the
freshly-exposed surfaces produced by road cutting and mining. Planting of grasses,
shrubs, trees and bamboos, followed by putting of jute net or vegetated stone
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