Analysis of the stability of the Xingguang bank slope in the Xiluodu Hydropower Station, China, under dry–wet cycles

The first impoundment of the Xiluodu Hydropower Station on the Jinsha River in Southwest China commenced in May 2013. A month after the first impoundment, the Xingguang bank slope began to deform and continues to do so to this day. This endangers the lives and properties of residents as well as the operation of the reservoir. The change in the shear strength index of the rock mass in the water level fluctuation zone under multiple saturation and drying conditions was studied using the dry–wet cycle test, and it was concluded that after 25 cycles, the shear strength index of the rock mass in the water level fluctuation zone of the bank slope decreased to the minimum. The cohesion and internal friction angle decreased by 29.77% and 20.31%, respectively. The Fast Lagrangian Analysis of Continua in three dimensions (FLAC3D) software was used to analyze the influence of water level change on bank slope stability. According to the simulation calculation, the stability coefficient of the bank slope decreased from 1.87 to 1.76 when the water level increased from 540 m to 600 m. However, the interior of the bank slope did not develop into a consistent shear strain increment concentration zone, indicating that an increase in the water level resulted in a decrease in the stability coefficient of the bank slope, but the bank slope remained stable as a whole. The results of the dry–wet cycle test were introduced into the numerical simulation. The results demonstrate that when the calculation time was more than 25 years, the maximum displacement of the extremely strong dumping area of the bank slope suddenly increased from 169 cm to 1691 cm, and the stability coefficient decreased to 1.11. According to the dry–wet cycle test and numerical simulation results, it can be determined that water storage in the reservoir area is a major cause of bank slope deformation and failure, and the bank slope may be unstable in the next 25 to 30 years. The bank slope may be destroyed in advance if the reservoir water level rises and falls frequently.