Geoscience Reference
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Consequently the angle of internal friction is far less than the regional slope
(60
) that sets in instability. Cohesion is very less and that cannot bind the soil
effectively.
°
With the onset of monsoon rill cutting as well as gully erosion starts and the run-
off, concentrating through these denuded portions, becomes the dominant agent
of soil erosion.
The geological deformation due to the pushing effects of the Damuda Series of
rocks of lower Gondwana period against the Daling Series.
Existence of very fragile rock-soil composition (rock waste of quartz-mica-
schist) over the slope surface.
Coarse textured soil with very low amount of cohesive substances like salt,
calcium, and magnesium with high degree of percolation and leaching of upper
soil materials to the bottom leading to disintegration and displacement of soil.
Unscienti
c coal dust drills and tunnels leading to rupturing of basal support.
Depletion of vegetation covers which increases surface run-off and soil erosion.
Concentration of settlement along the Hill Cart Road (NH-55) and their illegal
household activities over steep mountain slope and immense pressure over the
fragile slope materials by man-made concrete structure.
Physiographic con
guration (arcuate) of the Paglajhora sinking (major landslide
section) area provides favourable condition to produce hydrostatic pressure.
Proximity to Main Central Thrust (MCT).
Existence of intensely fractured and sheared nature of the bed rock.
Toe cutting and headword erosion of debris covered slope by a fast flowing
tributaries which losses the basal support.
Moderate to steep slope gradient which favours the concentration of water and
drainage.
Improper drainage network orientation throughout the region.
Accumulation of highly anisotrophic materials with a great thickness and low
shearing resistance.
Disintegration of phyllite and its surcharge with water caused by heavy
downpour.
Hill face, composed of phyllite and mica-schist, lost its shearing strength due to
saturation and tends to move downward in the name of failure.
The entire tea garden area is dominated by steep slope (>60
°
) and toe cutting by
narrow channels.
1.6 Types and Classi
cation of Landslide
The movement of the slope materials varies from place to place. Landslide can be
classi
ed based on the rate of movement of slope materials, the shape of the slope
surface, the materials in the slope movements and other criteria involved in causing
slope movement. Considering all these many researchers such as Heim (1882),
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