Geoscience Reference
In-Depth Information
Table 2.15 Volumetric expansion of the landslide with strength properties from Shiviter
Landslide
number
Volume
(1986)
(m
3
)
Volume
(June, 2006)
(m
3
)
Volume
(August,
2010) (m
3
)
Slope
angle
(
Ѳ
)(
°
)
Cohesion
(c)
Friction
angle
(
φ
)(
°
)
Water
holding
capacity
(%)
I
390
450
540
57
0.05
25
24
II
1,200
1,350
1,400
62
0.13
18
33
III
300
500
620
59
0.52
21
35
Source Laboratory test result
Table 2.16 Cohesion (c) and landslide potentiality index (LPIV)
Classes
Number of
pixels (F
1
)
No. of landslide
affected pixels (F
2
)
Landslide potentiality index
(LPI) = (F
2
/F
1
×
100)
<0.01
3,381
691
20.44
0.01
-
0.11
3,786
668
17.64
0.11
0.20
3,695
451
12.20
-
0.20
0.29
3,352
522
15.57
-
0.29
-
0.38
3,899
344
8.82
0.38
0.47
3,741
286
7.64
-
0.47
0.55
2,450
110
4.48
-
0.55
-
0.64
3,987
221
5.54
0.64
0.73
4,021
120
2.98
-
0.73
0.90
1,519
60
3.94
-
adopted from the
field experiences done by Deoja (Mountain Risk Engineering
Handbook,
1991
) and Speci
c Yield from Basic Ground-water Hydrology. Here,
the wet soil density was derived after Brasher (
1966
). Higher the density, greater is
the propensity of landslide occurrences. Wet soils help to liquify the mineralogical
properties present in the soil and reduce the cohesive strength.
The wet soil density plays a signi
cant role in changing chemical properties,
cohesion (c) and friction angle (
) of the soil particles. It is proved that greater is the
wet soil density, lesser is the cohesive strength of the soil because after wetting the
soil, it loses internal bonding capacity and becomes more susceptible to landslide.
In Shivkhola watershed, wet soil density is higher (>2.00 KN/m
3
) in the areas of
Tindharia, 14 Miles Bustee, Paglajhora, Sepoydhura, Gitingia and Upper Paglajh-
ora (Fig.
2.16
). All these places are dominated by drainage concentration. Such
drainage concentration helped to increase the wet soil density and to reduce the
cohesive strength. The study on landslide potentiality shows that soils having high
wet soil density are very much prone to landslide phenomena (Table
2.17
).
φ
Search WWH ::
Custom Search