Stability reassessment and optimization of construction procedure for left bank dam shoulder slope

The stability of the left bank dam shoulder slope of the Kala Hydropower Station is critically assessed due to the significant unloading and disturbance from excavation. This study integrates geological analysis, numerical modelling, and stability assessments to propose an optimized construction procedure. The results of the stability analysis indicate that, under natural conditions, the safety factor of the slope section is 1.20, with potential slip instability zones identified between elevations 2050m to 2210m. When subjected to excavation, the safety factors for two proposed support schemes under natural, saturated, and seismic conditions are 1.14, 1.06 and 1.06 (scheme 1); 1.30, 1.22 and 1.22 (scheme 2), respectively. The findings demonstrate that reducing the excavation height does not compromise slope safety, provided appropriate reinforcement measures are applied to the natural slope within the upper 100 meters, and support scheme 2 is recommended to apply when excavated to EL. 1995m. Numerical simulations using the Strength Reduction Method (SRM) and the UDEC model reveal that slope stability is controlled by outward dipping unloading cracks (e.g., Lc72 and Lc122) and fractured rock masses. Both support schemes propose anchor bolt and cable reinforcements to mitigate instability risks. This study provides valuable insights for improving the construction procedures and ensuring the long-term stability of the dam shoulder slope.