Dynamic response and phreatic line calculation model of groundwater in a reservoir landslide: Exemplified by the Shiliushubao landslide

Reservoir water and rainfall directly lead to the change in groundwater levals, which is the main factor inducing landslide. Most of the existing studies discuss the influence of reservoir water and rainfalls on landslide deformation based on monitoring data, and fail to reveal the groundwater response law of the reservoir landslide. The groundwater saturation line calculation model does not consider the influence of rainfall and reservoir water at the same time, and the boundary conditions of the model are quite different from the actual situation of the reservoir landslide. The research is to reveal the dynamic response law of groundwater in a reservoir landslide, and construct a calculation model of groundwater phreatic line closer to the actual situation. The dynamic monitoring of the groundwater levels in the Shiliushubao landslide of the Three Gorges Reservoir was carried out, and the results reveal the dynamic response law of the groundwater levels of the landslide under the conditions of the reservoir water rise and fall and rainfall. The groundwater seepage field is similar to the laminar flow. The groundwater levels in the front and middle of the landslide are almost synchronized with the reservoir water level. The groundwater levels in the rear of the landslide are mainly affected by rainfall. Daily rainfall of 30 mm will cause obvious changes in the groundwater levels. The differential equation of landslide groundwater unsteady seepage under the coupling condition of periodic reservoir water level fluctuation and random rainfall is analyzed and established. Subsequently, the calculation model of the groundwater level infiltration line of the landslide of the reservoir is set up and used for the actual monitoring results to verify the accuracy of the modified model. The calculation results of the calculation model are employed to analyze the seepage field of the landslide under different working conditions, and it is concluded that the reservoir water level can affect the landslide within about 145 m from the front edge. The rainfall and reservoir water level change the thresholds that trigger groundwater changes are 0.03 m/d and 0.1 m/d, respectively, and there are certain differences in the impact of rainfall and reservoir water level on the groundwater levels under different combinations of working conditions.