An investigative assessment of the stability of natural and road-cut rock slopes using empirical rock mass classification systems and numerical methods: case study of NH-07 from the Garhwal Himalayas, India

The Garhwal Himalayan region of India is increasingly susceptible to landslides due to the highly deformed and weathered nature of the discontinuity infested rock slopes with complex geological settings and active tectonics. Unscientific planning and construction of the road-cut rock slopes coupled with heavy monsoonal rainfall in the region often trigger landslides causing loss of lives, property damages, and disruption of traffic movements. In the present study, a road stretch (of ~ 61 km length) along NH-07 between Karnaprayag and Langsi in Garhwal Himalayas of Uttarakhand, India was studied and 25 slopes exhibiting potential failure mechanisms were identified whose stability grades were assessed qualitatively using empirical rock mass classification techniques such as Geological Strength Index (GSI), Rock Mass Rating (RMRbasic), Slope Mass rating (SMR), Continuous Slope Mass rating (Co-SMR), and Chinese Slope Mass Rating (CSMR). Furthermore, numerical modelling of the identified slopes was also carried out by deterministic and probabilistic approaches using both limit equilibrium method and finite element method, following which the results of the qualitative and quantitative analyses were compared. The results of SMR and Co-SMR techniques were found to be in close agreement with the field conditions. Lastly, engineered rock slope designs were proposed for a few slopes in the form of support system using rock bolts. The coherent methodology of this study using analytical and numerical methods shall provide critical assessment of the slopes for formulating necessary guidelines for the appropriate design of control measures.