Evolution of mining-induced fractured zone height above a mined panel in longwall coal mining

The accurate determination of the height of a fractured zone is vital in preventing water inrush and reducing the risk of disasters. However, understanding the fractured zone height evolution process remains a significant challenge in mining activities. In this study, the caving characteristics of overlying strata were investigated experimentally to determine the height of a fractured zone based on the geological conditions of No. 4308 Face ChengZhuang Coal Mine, China. The fractured zone heights were compared with those measured using physical experiment, 3DEC simulation, and a time-dependent energy model, and their results were verified against one another. The gas drainage method was used to validate the mining-induced height evolution and boundary. The results showed that the height of the fractured zone exhibits a stepped increasing trend. It increases slowly at the beginning of strata collapse and when mining-induced fractures approach the key stratum. The key stratum considerably affects the evolution of fractured zone height and may also influence the destressed zone boundary in the horizontal direction. In the destressed zone with a lower height, longwall mining rapidly affects strata, and the gas stored in lower overlying strata, which is unstable due to the movement of strata, is released rapidly. The cross-measure boreholes can drainage more gas in the middle of the mining-induced fractured zone because of the relatively stable strata and penetrating fracture. Overall, the results provide references for assigning cross-measure boreholes and a high gas drainage gallery to ensure safe conditions in a coal mine.