Confined water migration and failure of the extra-thick sandstone aquifer above multilongwall faces -A case study

The overburden extra-thick sandstone confined aquifer in underground coal mines also functions as a key stratum. Its failure and the associated confined water migration have a substantial impact on mine safety. A field case involving an overburden extra-thick Luohe confined aquifer (LHA) was introduced, and long-term ground monitoring up to 6 years of water level in LHA was conducted. A comprehensive analysis was carried out on the failure process of the overburden extra-thick LHA and its relationship with confined water migration. The influence of the confined water drainage in the extra-thick LHA on the mining-induced stress field and the reasonable panel size under the extra-thick LHA were discussed. The results indicate that water-level variations in LHA exhibit a phased pattern and significant changes in LHA water level and goaf water inflow occur when the panel goaf reaches the square stages, especially when the LHA breaks. The mining-induced drainage of confined water in the LHA transfers a greater portion of the roof load to the surrounding rock, intensifying stress concentration and the risk of dynamic disasters. For mine water conservation and dynamic disaster prevention, panel dimensions beneath the extra-thick LHA should be scientifically predetermined.