A geotechnical investigation on a recent gigantic rock avalanche at the Patalganga-Langsi site on the Badrinath highway of chamoli, Uttarakhand (Garhwal Himalaya), India

Garhwal Himalaya is one of the most landslide-prone regions in the Himalayan Belt due to its seismo-tectonic background, geological complexity, climate, geomorphological setting and large-scale human interference. A gigantic rock avalanche happened on July 10, 2024, near Patalganga-Langsi Tunnel on the Badrinath Highway (NH-7) of the Chamoli district and disconnected the Joshimath, Badrinath, and Nanda Devi National Park for a few hours. This road corridor is a significant gateway for valued pilgrimage destinations and Indo-Tibet Border security. A detailed investigation has been done on the recent reactivated rock cum debris avalanche at the Patalganga-Langsi Tunnel site. The Artificial Neural Network (ANN) model identifies this area as a high landslide susceptible zone, and the entire Patalganga-Langsi is tectonically controlled by the Main Central Thrust (MCT) and other proximity minor thrusts. Rainfall and exposed slope conditions are the primary triggering factors behind this rock avalanche, and geologically, this slope is still vulnerable as the Factor of Safety (FoS) is near the threshold value (1.019). Subsequently, the Schmidt hammer rebound test showed poor rock strength (approximately 30 or sometimes below 30), and the rocks have numerous structural signatures, which make them more vulnerable. Results of kinematic analysis for the two studied road cut slopes (Slope 1 and 2) emphasized a tendency to wedge failure. After the geo-technical study and the hazard potential of the slide site, sustainable geo-environmental management techniques should be immediately executed to maintain the socio-economic lifeline as well as Indo-Tibetan Border security management. Geo-technical parameters of the Patalganga-Langsi site reflect that there is a very high probability of wedge-type rockfall and rock-cum-debris fall.