Analyses of Different Slope Failures along the Road Sections of West Sikkim, India using Rock Mass Classification and Kinematic Analysis Approach

Abstract

Slope failures along the road sections cause huge problems every year in Sikkim. A slope instability analyses was performed along the road sections in parts of West Sikkim. The study was supported by geotechnical analyses like rock mass rating (RMR) and slope mass rating (SMR). In order to identify different failure types stereographic plotting based kinematic analyses was performed. Out of 33 study sites for the geotechnical analyses, 24 sites were identified as wedge failure and the remaining 9 sites were identified as the planar failure. Highly metamorphosed rocks like quartzite, phyllite and gneiss were the common rocks found in the area, comprising the discontinuities like joints were found up to 4 sets in certain locations. Other tectonic discontinuities include main central thrust (MCT), Tista lineament and other inferred thrust. Several such structural discontinuities and the weak lithology have made the area extremely vulnerable. The RMRbasic values varies from 26-60 in the study area which falls in the good to average category rocks. Adjustment factors were added to the RMR_basic to calculate the SMR values, which ranges between 26- 74 and falls in good to bad rock mass description. Based on the different values for the SMR ratings, supportive measures were recommended for the different study locations. These are spot or systematic bolting, spot shotcrete, systematic anchors, systematic shotcrete, toe wall, dental concrete, systematic reinforced shotcrete, re-excavation, deep drainage, etc. and bioengineering treatment.