Rainfall-Induced Seepage and Drainage Stabilization of a Cold-Region Internal Waste Dump Slope Under Prescribed Moisture and Temperature States

Rainfall-induced seepage instability is a major concern for internal waste dump slopes in cold-region open-pit coal mines, where slope performance is influenced by groundwater conditions, moisture state, and seasonal temperature variations. This study investigates the internal waste dump slope of the Chaoyang open-pit coal mine and evaluates its seepage and stability responses under prescribed moisture and temperature states before and after rainfall, together with the effectiveness of drainage control. Soil specimens with moisture contents of 14%, 17.6% (natural), 23%, and 26% were tested at ambient temperature, −5 °C, and −15 °C by uniaxial compression and direct shear tests. The mechanical parameters measured under the prescribed moisture and temperature states were assigned to a GTS NX seepage–stability model. Twenty-four parametric cases, comprising four moisture contents, three temperature states, and pre- and post-rainfall conditions, were evaluated using the strength-reduction method, and an HDPE perforated drainage scheme was subsequently assessed. Under the ambient-temperature parameter state, increasing specimen moisture content from 14% to 26% reduced the pre-rainfall factor of safety from 1.41 to 1.18 and the post-rainfall value from 1.38 to 1.17. Parameter sets obtained from low-temperature-conditioned specimens produced higher calculated factors of safety; however, these cases represent prescribed mechanical states rather than the actual winter condition of the full-scale slope. Under the idealized drainage boundary, the pre- and post-rainfall factors of safety increased from 1.22 and 1.18 to 1.40 and 1.39, respectively. The results demonstrate the relative effects of laboratory-derived mechanical parameters, rainfall-induced seepage, and idealized drainage under the prescribed scenarios.