Integrated empirical and numerical approach for stability and failure analysis of cut slopes in seismically active Uttarakhand Himalayan, India

Abstract

In the recent past, the upper range of the Himalayas witnessed numerous cases of disasters (such as Kedarnath tragedy) and was responsible for huge destructions and instability of many slopes along the National Highway (NH-7) Uttarakhand, India. The crucial part of the road passes through cut slopes comprised of highly jointed rock mass and strong variation in persistence, spacing, and degree of fracturing observed at different locations. As the area is located in the seismically active Lesser Himalayan region, where numerous slope failures of great magnitude may be anticipated. This study was carried out to predict the potential instability of eight different slopes along NH-7 from Kaudiyala to Karakot, Uttarakhand, using empirical and numerical methods. Preliminary stability assessment includes rock mass characterization, kinematic analysis, and continuous slope mass rating (CoSMR), where rocks are generally blocky (fair surface) and undergoes mostly wedge failure. CoSMR and Qslope, both indicate that three locations are partially stable, while the rest of the other locations are unstable. Results of newly developed [BQ] and [BQ]GSI systems are closely associated and classify slopes under partially stable (class III & IV) and unstable (class V), respectively. Afterward, an exhaustive study was carried out with numerical methods to inquire into failure mechanism and associated damage zone. The factor of safety was estimated from limit equilibrium, finite element stress-based approach, and continuum finite element method, where the majority of slopes are critically stable and unstable except few stable slopes. Further, the application of seismic loading substantially incited the slope instability, and result shows that the reduction in a static factor of safety is ranging from 22.22 to 50%, with an average of about 34.24% using different numerical methods. Additionally, seismic forces also alter the profile of stress–strain, strength, displacements, and other parameters predicted under the condition of gravity. Nonlinear Generalized Hoek-Brown failure criterion supersedes Mohr-Coulomb criterion failure almost in each profile and provides most vulnerability and authentic result in seismically active jointed rocks of Himalayan.