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Himalayan Geology, Vol. 31
(2), 2010, pp. 125-132, Printed in India
Surface and sub-surface characterization of Byung landslide in Mandakini
valley, Garhwal Himalaya
SHIPRA CHAUDHARY, VIKRAM GUPTA*, Y.P. SUNDRIYAL
Dept. of Geology, H.N.B. Garhwal University, Srinagar (Garhwal): ypsundriyal@yahoo.co.in
*Wadia Institute of Himalayan Geology, 33, G. M. S. Road, Dehra Dun
*Email:
vgupta_wihg@yahoo.com
Abstract: The Byung landslide located in vicinity of village Khumera
on the National Highway (NH-109) in the Mandakini valley was triggered
following 16th July 2001 cloudburst and is active since then. It is a
typical example of ‘Complex landslide’. The landslide zone measures about 80
m in length, 110 m in width and has maximum vertical displacement of 3.10m.
The total surface area affected by the landslide is about 0.363 km2. The
granulometric analyses indicate that the soil within the subsidence zone
contains lesser proportion (~ 20.3%) of fines (silt + clay) than the soil in
the environs (~32.2% - 37.8%). The lesser proportion of fines in the
subsidence zone may be attributed to their washing away by continuous
percolation of water into the hill slope by four drainage channels viz,
Khumera, Dhom, Dhom-1 and Syul located within the landslide zone. However,
the shear-strength characteristics of the soil in the landslide zone
indicate their resistances against sliding with cohesion and friction angle
ranging between 30.32 kN/m2 and 48.08 kN/m2 and 23.91° and 38.29°,
respectively. The Ground Penetrating Radar (GPR) sub-surface data confirms
that the subsidence is not caused by any sub-surface structural feature. The
high percentage of fines constituting the hill slope combined with short
duration high intensity rainfall leading to cloudburst on 16 July 2001 is
mainly responsible for initiation of this landslide.
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