Geoscience Reference
In-Depth Information
geo-technical attributes include surface inclination (
ʲ
), soil depth (z), cohesion (c),
angle of internal friction (
φ
), soil saturation index (m), soil density (
ʳ
s
) and density
of water (
ʳ
w
). Before planning any land use, the better understanding and inves-
tigation of geo-tectonic parameters and the preparation of a stability distribution
map by applying GIS tools are very much popular and accepted approach in the
present time. The major objective of the present study is to study geo-technical
parameters and to identify the potential stability sites in the Shivkhola Watershed
through estimating the strength parameters and the application of 1D slope Stability
model to prepare landslide susceptibility maps. The validity of the prepared land-
slide susceptibility maps under dry, semi-saturated and saturated condition were
evaluated by means of a frequency ratio (FR). Finally, an accuracy assessment was
made by ground truth veri
cation of the existing landslide locations where the
classi
cation accuracy for dry, semi-saturated and saturated condition was 93.86,
94.58 and 85.44 % respectively.
6.2 Materials and Method
6.2.1 Slope Stability Model Concept
Two forces are responsible to determine the stability condition i.e. driving force
(shear stress) and resisting force (shear strength). Shear stress is given as,
˄
=
ʳ
D sin
⊝
cos
⊝
(where
ʳ
, soil density; D, depth of the soil;
⊝
, slope angle) and
shear strength of Mohr and Columb de
ned as, S = c +
˄
tan
φ
(where c: cohesion;
φ
: shear stress). Saturated slope material increases instability with
increasing pore water pressure. The pore water pressure depends on unit weight of
water (
: friction angle;
˄
ʳ
w
) and the height of water (D
w
) above the failure plane surface. The height
of the water shows the ground water condition in the soil. In this case the shear
resistance of the soil is given by the following:
2
S=c+
ð
cc
w
m
Þ
D
cos
€
tan
u
ð
6
:
1
Þ
where, m is saturation index which shows the saturation condition of the soil.
If the value of m equals to 1, the soil is completely saturated and the value of 0
indicates complete dry condition.
In many investigations of natural slope stability, infinite slope analysis had
frequently been used because of its relative simplicity where the thickness of the
soil is smaller than the length of the slope.
For realistic modeling 3D failure mechanism should be considered which
includes different depth of sliding surface throughout the slope failure mass. Soeters
and Westen (
1996
) recommended using in
nite slope stability analysis in order to
conduct deterministic analysis of the large area and due to complication in estab-
lishing vertical depth of failure plane in 3D mechanism. Monte Carlo Method, a
simpli
ed approach was considered by them reducing 3D depth to 2D equivalent
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