Geoscience Reference
In-Depth Information
Table 2.13 Result of laboratory analysis (GSI Lab.) of collected soil samples from Tindharia
Sample
Cohesion (C)
Friction
angle (
Dry soil
density
(gm/cm
3
)
Wet soil
density
(gm/cm
3
)
Water holding
capacity (%)
φ
)
I
0.64
22
°
30
′
2.20
2.43
35
II
0.25
19
°
2.10
2.29
29
II
0.08
24
°
1.99
2.21
28
expansion are low than the pore space. The pore space even at the depth of 60
80 cm
is prevailing above 35 %. The easy percolation of water through the subsurface soil
pore spaces creates the slope more vulnerable to soil erosion and slope instability. On
the other hand, near railway station and other places of Tindharia there is higher rate
of water holding capacity ranging between 40 and 55 % (Table
2.13
) up to the depth
of 40 cm. where the percentage of pore space is experiencing 30
-
50 %. The water
holding capacity is reduced with decreasing the pore space beyond the depth of
60 cm. The volumetric expansion takes place in proportion to pore space and water
holding capacity and it is high (>10 %) above the depth of 40 cm and shows the
gradual decreasing tendency below the depth of 40 cm.
In the Shiviter T.E. the moderate to high percentage of pore space helps soil to
hold the moisture content and to expand moderately. The presence of sand, silt and
clay at moderate amount within the soil has helped to retain the moisture for a long
time without downward movement and has caused slope material more vulnerable
to soil loss. In the middle section of the watershed the water holding capacity as
well as the pore spaces is very high but there is a uniform rate of decreasing
tendency of both the parameters. The volumetric expansion is not as high as the
water holding capacity and pore spaces. The water holding capacity and pore space
is more than 50 % up to the depth of 40 cm when the volumetric expansion ranges
between 10 and 20 %. Beyond 40 cm water holding capacity and pore space are
experiencing 45
-
10 % volumetric expansion takes place. The
decreasing of volume expansion, pore space and water holding capacity are in the
same rate at Upper Paglajhora and Tindharia T.E. The percentage of pore space is
very high up to the depth of 30 cm and that is why the water holding capacity is
reduced sharply and beyond 60 cm depth the pore space is being decreased
remarkably which causes easy saturation of surface soil and volumetric expansion
also takes place within the sub-surface soil. Such condition reduces the cohesion
and internal friction of the slope materials and makes the slope very much prone to
shallow soil slip. It is to be concluded from the present study that the average
percentage of sand and granules up to the depth of 100 cm are 35 and percentage of
silt is around 15 which promotes the soil layer to be saturated very easily and also
reduces the cohesion and shearing strength of the soil. Pore spaces, water holding
capacity and volumetric expansion decrease with increasing depth everywhere
which indicates that the near surface soil layer is saturated easily that reduced its
cohesion and shearing strength.
15 % where 0
-
-
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