Characteristic of the infiltration recharge effect in coal mine under reservoirs

To address the critical scientific gap in quantifying fracture-dominated seepage mechanisms under reservoir dynamic loading, this study proposes an integrated methodology combining in situ double-ring infiltration experiments (n = 68), particle gradation analysis, and a novel fracture-porosity dual-domain model to assess groundwater recharge and reservoir leakage risks during coal mining beneath the Hongyanhe Reservoir. Key findings reveal: The vadose zone lithology (loess/weathered sandstone/silty clay) exhibits extremely low permeability (K = 6.52 × 10⁻⁷-3.47 × 10⁻⁸ cm/s), providing effective anti-seepage barriers; saturation-driven flow is gravity-dominated, with infiltration rates of 0.000029-0.000563 m/d across lithologies; Reservoir seepage loss at the 4105 working face is 5.9 ± 0.7 m³/d (95% CI), which is lower than conventional model predictions and poses no risk to mine safety; Field observations suggest that fracture density and silt layer thickness are primary controls of seepage variability. This work establishes the first physics-based framework for safe coal extraction under reservoirs, releasing 2.1 million tons of otherwise stranded resources while ensuring reservoir integrity. Results provide a decision-making benchmark for global mining under water bodies.