Prediction and early warning analysis of reservoir bank slopes based on anti-sliding stability evolution

The stability of reservoir bank slopes during the impoundment period has become a critical issue in the construction and operation of large-scale hydropower projects. A predictive and early warning method for reservoir bank slopes is proposed, based on slip resistance stability evolution analysis. Using a refined three-dimensional numerical calculation model of the bank slope, the creep damage model is employed for simulation and analysis, enabling the derivation of stress field and strain field evolution from bank slope excavation to the long-term impoundment period. Subsequently, for the stress field of the bank slope at any given moment, the safety factors of the sliding blocks are determined by using the multigrid method and vector sum method. Accordingly, the evolutionary law of the sliding safety factor for the bank slope can be derived. By integrating the long-term stability evolution trend of the slope with specific engineering practices, the safety factors for graded warning can be determined. Based on the time correspondence, the graded warning moment and the deformation warning index for slope measurement points can be determined. In this study, the proposed method is applied to the left bank slope of the Jinping I Hydropower Station. The results indicate that from excavation to June 2022, the left bank slope exhibits a strong correlation with excavation elevation and the number of reservoir water cycles. The initial, maximum, and minimum safety factors are 2.01, 3.07, and 1.58, respectively. The deep fracture SL_44-1 serves as the primary stress-bearing slip surface of the left bank slope, while the safety margin of the fault f_42-9 and lamprophyre X is slightly insufficient. Based on the long-term stability evolution trend of the slope and in accordance with relevant standards, the safety factors for graded warning indicators—K_w1, K_w2, K_w3, and K_w4—are determined as 1.350, 1.325, 1.300, and 1.275, respectively. Correspondingly, the estimated warning times are 12/30/2066, 12/30/2084, and 12/30/2120. Accordingly, the deformation graded warning indexes for slope measurement points are established.