Geoscience Reference
In-Depth Information
Table 2.3 Rock properties
Rock types
Strength (MN/m
2
)
Bulk density (Mg/m
3
)
Porosity (%)
Compressive
Tensile
Shear
Granite
100
250
7
25
14
40
2.6
2.9
0.15
1.5
-
-
-
-
-
Gneiss
50
200
5
20
2.8
3.0
0.5
1.5
-
-
-
-
-
Slate
100
-
200
7
-
20
15
-
30
2.6
-
2.7
0.1
-
0.5
Sandstone
20
170
4
25
8
40
2.0
2.6
5
25
-
-
-
-
-
Shale
100
200
7
20
15
30
2.0
2.4
10
30
-
-
-
-
-
Source Attewell and Farmer (
1976
)
geological report on the hill slope stability in and around Darjiling Himalaya.
Attewell and Farmer (
1976
) studied compressive, tensile and shear strength of
various rocks and concluded that slate and shale have low range of shear strength
(Table
2.3
). Sandstone is characterized by high range of shearing strength. The bulk
density (Mg/m
3
) in most of the rocks varies from 2.00 to 2.9. In the Shivkhola
Watershed, Damuda and Swialik rock groups depict high range of shearing strength
where porosity ranges from 5 to 25 %.
2.2.5 Analysis of Lineaments and Landslide Potentiality
The lineaments exhibit the zone of weakness surface providing some linear to
curvilinear features such as fracture, joint, fault etc. in the geological structure
(Fig.
2.5
). To extract lineaments of the Shiv-khola watershed PCI-GEOMATICA
Software of GIS was used and in the extraction process 3 bands of wavelength were
taken into account such as Near Infrared (Band-I; 0.7
1.3
µ
m), Red (Band-II;
-
0.6
0.7
µ
m) and Green (Band-III; 0.5
0.6
µ
m). The algorithm used to prepare
-
-
lineament map is
. The lineaments at the places of Lower
Paglajhora, Gayabari lower, Tindharia, 14 Miles Bustee, Shiviter Lower slope,
Sepoydhura, and Norbong T.E. are closely spaced. The lineaments are absent at
extreme north, north-east and eastern marginal part of the Shivkhola Watershed.
The LPIV of each lineament class exhibits that the greater the distance from the
lineaments lesser is the probability of landslide phenomena. The distance of 125 m
from lineaments is dominated by high percentage of landslide affected pixels as
well as high landslide potentiality index value of more than 17. The distance of
more than 600 m from lineaments is less affected by landslide where LPIV ranges
from 0 to 10 (Table
2.4
).
'
lineament extraction
'
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