A review of mine water stratification in abandoned flooded coal mines

Mine water stratification is a common natural phenomenon in flooded coal mines, with important implications for managing water inrush pollution and harnessing geothermal resources in abandoned mines. Based on a thorough review of nearly 60 years of domestic and international research, this study systematically summarizes the progress in understanding the characteristics of mine water stratification, its formation mechanisms, stability assessment methods, disturbance response processes, research approaches, and practical applications. The research results indicate that: ① mine water stratification is primarily driven by density differences caused by variations in temperature and salinity, and is jointly influenced by geological structures, connectivity patterns, roadway layouts, and recharge modes. ② Buoyancy ratio, buoyancy frequency, and Richardson number are three representative parameters used to assess the stability of stratified water bodies, each reflecting different physical mechanisms within the system. ③ Existing observational methods include field sampling, laboratory experiments, and numerical simulations, with the double-diffusive convection model being widely accepted and applied. ④ Mine water stratification enables accurate pollutant identification, layer-specific extraction, and targeted treatment in mine water pollution control, improving cost-effectiveness and efficiency. In geothermal development, it supports optimized pumping layouts and the efficient utilization of low-temperature thermal energy. ⑤ In response to engineering needs, future research should focus on key challenges such as the full evolutionary mechanism of mine water stratification, mine water stratification behavior under complex multi-layer and multi-source recharge conditions, mine water stratification patterns in interconnected multi-mine roadway systems, disturbance mechanisms, and the development of artificial regulation strategies.