Study on deformation mechanism and parameter inversion of a reservoir bank slope during initial impoundment

The stability of reservoir bank slope during impoundment is significant for the safe operation of hydropower stations. The deformation evolution of a slope adjacent to dam is analyzed based on the field monitoring data. The main influencing factors and spatial distribution of the slope deformation during impoundment are identified based on the multiple regression model and K -means cluster analysis, respectively. Subsequently, the deformation mechanism of the slope is analyzed by three-dimensional nonlinear finite element method. Then, an inversion analysis method based on improved adaptive genetic algorithm and back propagation neural network is proposed. The measured deformations of 44 monitoring points are used to inverse a total of 27 mechanical parameters, including deformation parameters, strength parameters and Biot coefficients of 9 materials. Finally, the influence of sample numbers on the prediction accuracy and the robustness of the neural network are discussed. The results indicate that the deformation rate of the slope is substantially associated with the impounding process. The water pressure component and aging component of the deformation account for a relatively high proportion while the temperature component is negligible. The deformation is mainly affected by material softening and effective stress of shallow-buried fractured rock mass, in which the latter dominates. The water load on the dam surface is the deformation inducement of the deep rock mass. The proposed inversion method can reasonably obtain the weakening rate of materials and make the numerical model accurately fit in with the actual state of the slope.