Temperature–moisture–rainfall effects on internal dump slope stability in a cold-region open-pit coal mine with drainage validation

Internal dump slopes in cold-region open-pit coal mines are subjected to moisture variation, freezing temperatures, rainfall infiltration, and groundwater seepage. This study developed an integrated experimental-numerical-field framework to evaluate these effects for the Chaoyang open-pit coal mine in Heilongjiang Province, China. Unconfined compression and direct shear tests were conducted under four moisture contents of 14.0%, 17.6%, 23.0%, and 26.0% and three temperatures of 23 ± 2°C, −5°C, and −15°C. The measured elastic modulus, cohesion, and internal friction angle were incorporated into a three-dimensional GTS NX model to assess slope responses before and after 72 h of rainfall.At room temperature, increasing moisture content reduced the elastic modulus from 1802.4 to 1003.6 MPa and cohesion from 18 to 10 kPa, while the pre-rainfall factor of safety decreased from 1.405 to 1.176. Under subzero conditions, stiffness and cohesion increased because of pore-ice bonding, whereas the internal friction angle varied only modestly and non-monotonically. At −15°C, the post-rainfall factor of safety ranged from 1.478 to 1.537, and rainfall-induced reductions under all subzero conditions remained below 0.60%. Under the room-temperature natural-moisture condition, drainage pipes increased the factors of safety before and after rainfall from 1.221 and 1.184 to 1.413 and 1.384, respectively. Field monitoring recorded an average drainage discharge of 2.51 × 10 4 m 3 /day and groundwater-level drawdowns of 12.19 and 9.94 m in the upper and middle aquifers.The results demonstrate that moisture weakens unfrozen dump materials but can enhance frozen-state strength through ice bonding. The integration of laboratory-derived temperature-moisture parameters, three-dimensional rainfall analysis, and field hydraulic validation provides a practical framework for stability assessment and drainage control of cold-region internal dump slopes.