LANDSLIDES
A landslide is a geological
phenomenon which includes a wide range of ground movement, such as rock falls,
deep failure of slopes and shallow debris flows, which can occur in offshore, coastal and onshore environments.
CAUSES OF LANDSLIDES: - In
general, the factors which influence whether a landslide will occur typically
include slope angle, climate, weathering, water content, vegetation,
overloading, geology, and slope stability. Typically, a number of elements will
contribute to a landslide, but often there is one which triggers the movement of material.
Natural causes include:
v Elevation of pore water pressure by saturation of slope material from either intense or prolonged rainfall or seepage.
v Vibrations caused by earthquakes.
v Undercutting of cliffs and banks by waves or river erosion.
v Volcanic eruptions.
Human causes include:
v
Removal of vegetation.
v
Interference with, or changes to, natural drainage.
v
Leaking pipes such as water and sewer reticulation.
v
Modification of slopes by construction of roads, railways,
buildings, etc.
v
Overloading slopes.
v
Mining and quarrying activities.
v
Vibrations from heavy traffic, blasting, etc.
v
Excavation or displacement of rocks.
PREVENTION OF LANDSLIDES: -Listed below are some common
remedial methods used when landslide-prone slopes cannot be avoided. There is
no guarantee that any one method or combination thereof will completely
stabilize a moving hillside.
(i)
Improving
surface and subsurface drainage: Because water is a main factor in landslides, improving surface
and subsurface drainage at the site can increase the stability of a
landslide-prone slope. Surface water should be diverted away from the
landslide-prone region by channeling water in a lined drainage ditch.
(ii)
Excavating
the head: Removing the
soil and rock at the head of the landslide decreases the driving pressure and
can slow or stop a landslide.
(iii)
Buttressing the toe: If the toe of the landslide is
at the base of the slope, fill can be placed over the toe and along the base of
the slope. The fill increases the resisting forces along the failure surface in
the toe area.
(iv)
Constructing
piles and retaining walls:
Piles are metal beams that are either driven into the soil or placed in drill
holes. Properly placed piles should extend into a competent rock layer below
the landslide.
(v)
Removal
and replacement:
Landslide-prone soil and rock can be removed and replaced with stronger
materials, such as silty or sandy soils.
(vi)
Preserving
vegetation: Trees,
grasses, and vegetation can minimize the amount of water infiltrating into the
soil, slow the erosion caused by surface-water flow, and remove water from the
soil.