Geotechnical Insights of the Cut Slopes Along Silchar-Haflong National Highway, Assam, India

Insufficient geological research and a limited understanding of ground conditions during the design phase often led to slope failures and subsequent repair costs. This issue is notable in the 104 km Silchar-Haflong National Highway in Assam, India, located in the northwestern part of the Assam-Arakan folded mountain range. Over 158 slope failures have occurred due to various geo-climatic factors aggravated by human activities. A comprehensive engineering geological investigation was conducted on a 25 km section, using techniques like RMR_basic, SMR, Q_slope to assess slope conditions at several locations. Stability analyses were carried out using finite element numerical method for both dry and saturated conditions, revealing four potentially unstable slopes (L3, L5, L7, and L8). Critical SRF values ranged from 1.15 to 1.72 for dry conditions, while they varied from 0.95 to 0.98 for saturated conditions. The study also examined rockfall analysis for slope L7, considering parameters such as translational velocity, rebound height, kinetic energy, and travel distance. The findings indicated a potential for falling blocks to reach the road and pose a significant risk. The study emphasizes the need for implementing appropriate measures to address informal slope excavation, or else there is a likelihood of increased frequency and scale of rainfall-triggered roadside slope failures.