The Water−Holding Characteristics of Moraine in the Subsidence Area of Pulang Copper Mine

Moraine is the main sediment in the subsidence area of Pulang Copper Mine and the source of underground debris flow. Its unsaturated characteristics are related to the stability of subsidence area and occurrence of debris flow. Therefore, the soil−water characteristic experiments of moraine with different dry densities were carried out for the first time by the pressure plate instrument method, and the applicability of the Van Genuchten (VG) and Fredlund & Xing (FX) models for fitting the soil−water characteristic curves(SWCC) of moraine was evaluated. The evolution of the seepage field in the collapse area of Pulang Copper Mine within 24 h under different rainfall intensities was analyzed based on saturation−unsaturated mechanics. Higher dry density enhances water−holding capacity, increasing the intake air value and residual moisture content. Both VG and FX models effectively describe water−holding characteristics of glacial debris, with correlation coefficients greater than 0.95. However, However, the predicted value of the VG model in the residual stage is greater than the measured value. The topographic effect in the subsidence area is significant, and there is an obvious lateral seepage phenomenon during rainfall. The pore water pressure in the western region increases sequentially from the bottom of pit to the surface during rainfall, and the shape of the wetting line resembles that of the subsidence area. In the east, due to the terrain slope greater than 40°, a complete transient saturation zone would be formed inside the glacial debris, the variation of pore water pressure is controlled by rainfall density and tomography, and the wetting line gradually changes from irregular to similar to the shape of the subsidence area. The results can provide certain theoretical basis for the prediction of expansion of subsidence areas and the occurrence of underground debris flows.