Coal mine underground water reservoirs: A sustainable water storage solution for mining areas

Mine-based underground water reservoirs exhibit diverse designs and applications worldwide. Such water storage systems, constructed in active or abandoned mines, can significantly reduce water resource wastage and pollution in mining areas while improving water utilization efficiency. This review focuses on a typical form of coal mine underground water reservoir (CMUWR) composed of coal pillars and artificial concrete dams. From the micro, meso, and macro perspectives, this review systematically summarizes the qualitative and quantitative influences of mine water properties, load disturbances, wet-dry cycles on the stability of coal pillars, artificial dams, and surrounding rocks. At the microscale, specific attention is given to the deterioration mechanisms of rock and coal mineral particles under groundwater conditions with varying pH and salinity, revealing the physicochemical processes of water–rock reactions and categorizing typical degradation patterns with corresponding mitigation measures. At the mesoscale, based on laboratory mechanical experiments, the review outlines the loading conditions corresponding to different reservoir structures and synthesizes the quantitative weakening effects of loading mode, wet-dry treatments and duration, load magnitude, rate, and frequency on the strength of coal pillars, artificial dams, and surrounding rocks, while discussing the scaling relationship from laboratory to engineering practice. In the discussion section, from the macro engineering perspective, multiple practical cases of mine-based reservoirs worldwide are compared, the key technologies, advantages, and limitations of different reservoir types are summarized, and the current research gaps are highlighted. Finally, future directions are proposed, emphasizing the integration of experimental, modeling, and field-scale approaches to advance the development of CMUWR.