Depth-dependent mechanical-seepage behavior and safety mining distance of the steeply inclined coal mine underground reservoir

Coal mine underground reservoir (CMUR) technology mitigates water scarcity in China’s coal-rich western regions but lacks tailored solutions for steeply inclined coal seams. This study develops a novel framework of steeply inclined coal mine underground reservoirs (SICMUR), which is a paradigm shift from conventional CMUR that the coal seam itself serves as the reservoir floor, challenging conventional designs due to depth-dependent permeability and mechanical constraints. Triaxial mechanical-seepage tests on Xinjiang Wudong coal samples (100, 200, 300 m depths) revealed a 3.5 MPa triaxial strength increase per 100 m depth and a 58-fold post-peak permeability surge at 300 versus 100 m. Similar model simulations revealed mining-induced stress redistribution and significant deformation effects, particularly subsidence and water-conducting fractures during lower coal seam mining. Results indicate a minimum 40 m safety distance between reservoirs and lower coal seams. Critical construction parameters were investigated for Wudong mine SICMUR as collapse zone heights (9.9–12.31 m) and water-conducting fracture zone heights (31.96–37.40 m). This work systematically bridges SICMUR concepts to field implementation, offering a framework for water preservation in steeply inclined mining while addressing safety concerns, providing a new approach for water reservation in steeply inclined coal mining.