Chethanamba K.R. and G.R. Dodagoudar 1359 STABILITY ANALYSIS OF A LANDSLIDE USING DISTINCT ELEMENT METHOD Shilpa Pal 1 , Rajinder K. Bhasin 2 , Amir M. Kaynia 3 and Dilip.K. Paul 4 ABSTRACT In the present study an endeavour has been made to model Surabhi Landslide (longitudes 78 o 02 ’ and 78 o 04 ’ E and latitudes 30 o 28 ’ and 30 o 31 ’ N) in the Dehradun and Tehri districts of Uttaranchal located in Mussoorie, India. 2-D model has been simulated to understand the mechanism of the slide with the Distinct Element Method (UDEC) to decipher the weak zones (fractures) in the sliding area. Understanding the behaviour of this landslide will be helpful for planning and implementing landslide mitigation measures. In this study the area identified as the zone of detachment is the most vulnerable part of the landslide. With reduced friction angle due to ingress of water caused by heavy rainfall, the top layer of the zone of detachment starts moving. The total volume of the rock mass that becomes unstable is estimated as 11.58 million m 3 . The effect of degradation of discontinuities on the stability of the slope is simulated. In addition, the dynamic environment based on the amplification of the input loading, results in the instability of the top layer of the slide. Both sliding and rotation contributes to the failure of the blocks. The above studies have provided an insight into the deformation mechanism of the blocks formed by rock discontinuities. The discontinuum modelling presented in this study has helped to gain a better understanding of the stability of the landslide. INTRODUCTION It is often difficult to distinguish between earthquakes triggered landslides and static slope instabilities on the basis of geological environment and geomorphologic features alone. Indeed, both the size and the type of landslides induced under static or seismic conditions are quite similar. On the other hand, it seems that the location of the landslide scarps may provide indications about the origin of the mass movement. Landslides are one of the frequently occurring natural hazards 1 Asstt. Prof., Department of Civil Engineering, GCET, Greater Noida (U.P.) India sh6281pa@gmail.com Ph. No.:+918800325860 2 Senior Geologist, Rock and Foundation Engineering, NGI, PO Box 3930, Ullevaal Stadion, 0806 Oslo, Norway Rajinder.Kumar.Bhasin@ngi.no 3 Group leader, Earthquake Engineering and Numerical Modelling, NGI, PO Box 3930, Ullevaal Stadion, 0806 Oslo, Norway Amir.M.Kaynia@ngi.no 4 Professor, Department of Earthquake Engineering, IIT Roorkee, Roorkee – 247667 (Uttarakhand) India dpaulfeq@gmail.com