Analysis of the Deformation Mechanism of the Top Slope at the Inlet of the Lijiaxia Hydropower Station Diversion Tunnel

After long-term operation of the Lijiaxia Hydropower Station in Qinghai Province, following reservoir impoundment, the upper surface of the slope at the inlet of the diversion tunnel has exhibited noticeable deformation and tension cracks, posing a significant threat to the operational safety of the hydropower facility. To investigate the deformation mechanisms, evolution process, and underlying causes, as well as to evaluate the safety and stability of the slope, this study employed a comprehensive approach including drilling, testing, and field inspection. Detailed investigations were conducted on the slope's topography, stratigraphy, lithology, geological structures, deformation signs, geostress conditions, and hydrogeological characteristics. Based on monitoring data from nine observation points, three-dimensional modeling and numerical simulations were performed, complemented by stability analyses using limit equilibrium and strength reduction methods. Additionally, the potential height of landslide surges was calculated and predicted. Results indicate that the slope is currently in a critical state, with primary deformation modes being shallow surface collapse and overall creep-slip movements. Under natural conditions, the likelihood of a full-scale slide is low, and potential landslide surges remain controllable. Nearly six years of operational monitoring confirm that the slope deformation has largely stabilized, supporting the reliability of the prior mechanistic analysis and safety assessment. The methodologies and findings presented in this study provide a valuable reference for the analysis and evaluation of similar reservoir slope deformations.