Himalayan Geology, Vol. 42 (2), 2021, pp. 372-381, Printed in India
Geological and geotechnical studies of landslides located near Ichhari Dam Reservoir on Tons valley, Uttarakhand Himalaya
GAMBHIR SINGH CHAUHAN1*, H.C. NAINWAL1, VIKRAM GUPTA2
1Department of Geology, HNB Garhwal University, Srinagar Garhwal, Uttarakhand, 246174, India
2Wadia Institute of Himalayan Geology, Dehradun, Uttarakhand, 248001, India
*Email (Corresponding author): gambhirchauhan89@gmail.com
Abstract: Geological and geotechnical study of Ichhari and Pathua landslide zones located along the Minas road near the reservoir of Ichhari dam was carried out to delineate the causes of landslide, and to determine the Factor of safety (FOS). Ichhari landslide is a planar slope failure consists of rocks and debris. The Pathua landslide is a circular failure, and it contains debris material. Uniaxial compressive strength (UCS) and triaxial compressive strength (TCS) tests of rock core samples were performed to determine the shear strength (C and f). Sieve analysis of soil and debris material was carried out for grain-size analysis and the direct shear test of debris was used to determine shear strength. Liquid limit test was done for fine material. The results show that UCS and shear strength of rock mass in the Ichhari landslide varies at a large extent due to variation in weathering pattern and deformation of rocks. In the Pathua slide, the coarse-grained material of landslide shows low moisture content and liquid limit due to low proportion of fine material. It reflects that soil cannot remain stable under high water saturation condition. Study of tropical rainfall measuring mission (TRMM) data of monsoon season shows that maximum rainfall in the study area occurred in 2011 and 2013 is about 1420 mm and 1203 mm respectively. The Factor of safety (FOS) of Ichhari rock slide was determined using Limit equilibrium method. The value of FOS of 1.47 was obtained for saturated slope condition. The FOS of circular failure of Pathua slide was identified using the circular failure chart (CFC) method. The FOS value of 0.95, 0.91 and 0.84 were found for dry, 25%, 50% saturated slope conditions respectively. These results show that there are multiple causative factors responsible for landslides. Both landslides are stable under dry condition but become unstable after water saturation during raining season that causes reduction in the shear strength of landslide material.
Keywords: Landslide, Geotechnical study, Reservoir, Factor of safety, Tons valley, Uttarakhand Himalaya
