A New Method of Predicting the Height of the Fractured Water-Conducting Zone Due to High-Intensity Longwall Coal Mining in China

Violent movement of the roof rock and severe damage to the overlying strata occur in the large mined-out space left by rapidly advancing, high-intensity longwall coal mine extraction, as the goaf forms. Knowing the height of the fractured water-conducting zone (FWCZ) above the goaf is vital in the safety analysis of coal mining, particularly under a water body. The processes of overburden failure transfer (OFT) were analyzed for such high-intensity mining, divided into two stages: transmission development, and transmission termination. Rock failure criteria were used in theoretical calculations of the maximum lengths of 'suspended' (i.e., unsupported) rock strata, and of the maximum 'overhang' (i.e., cantilever) length of each stratum. Based on this, mechanical models of the unsupported strata and the overhanging strata were established. A new theoretical method of predicting the height of the FWCZ in this form of coal mining is put forward, based on OFT processes. A high-intensity mining panel (the 8100 longwall face at the Tongxin Coal Mine, Datong Coal Mining Group) was taken as an example. The proposed theoretical method, a numerical simulation method and an engineering analogy method were used to predict the height of the FWCZ. Comparison with in situ measurements at the Tongxin mine showed that the theoretical and numerical simulation results were in close agreement with measured data, verifying the rationality of the proposed approach.