Multidisciplinary Slope Stability Assessment in Weathered Metamorphic Rocks: A Case Study of the Highland Complex, Sri Lanka

Slope failure along road cuts on elevated terrains with structurally controlled weathered rock masses poses a significant geotechnical challenge. While rapid stability assessments are crucial, the intricate geotechnical behavior of rock masses complicates such evaluations. Kinematic analysis, Slope Stability Probability Classification (SSPC), Rock Mass Rating (RMR), Slope Mass Rating (SMR), Geological Strength Index (GSI), Q-slope methodology, and the limit equilibrium technique are widely employed in rock slope stability assessments. The application of these methods in structurally controlled, weathered, high-grade metamorphic terrains in tropical conditions, such as those found in Sri Lanka, has not been adequately researched. This study aims to bridge this gap by evaluating the stability of twenty-two road cuts along the Kandy-Randenigala and Kandy-Mahiyanganaya roads in Sri Lanka utilizing the aforementioned techniques. Results were compared with the actual stability conditions of the slopes and assessed the reliability of each method. The SSPC orientation-dependent analysis, Discrete SMR, Continuous SMR, and limit equilibrium analysis showed over 82% agreement with actual slope stability conditions. In contrast, the Q-slope method, based on maximum slope angle (β), proved unreliable in this context. Among these, Discrete SMR was the most reliable for assessing stability in structurally controlled weathered metamorphic terrains. The SSPC orientation-dependent probability analysis could also be recommended, particularly in scenarios without significant wedge failures.