Precise zoning control of coal seam gas in discontinuous mining face of strong outburst coal seams group

As shallow coal seams and easily exploitable coal resources gradually deplete, many old mines face challenges in gas management due to the complex gas occurrence in coal seams and irrational mining plans in the early stages. This results in stress accumulation affecting adjacent working faces during subsequent mining operations. Taking the Lu Ling Coal Mine Ⅱ944 working face as a case study, the author used numerical simulation methods to analyze the stress distribution caused by the residual coal pillars formed after discontinuous mining of upper and lower protruding adjacent layers. The study also obtained the permeability distribution characteristics in stress concentration zones through theoretical analysis, proposing the key technology of “disaster zoning for precise prevention”. The research reveals that the stress distribution of the Ⅱ944 working face shows a non-continuous spatiotemporal zoning pattern. When the temporal sequence of mining and leaving coal pillars in the upper and lower adjacent layers changes, the low-stress concentration zone in the middle coal layer can transform into a prominently stressed concentration zone, and the depressurized zone can transform into a stress concentration zone. These zones can be categorized as depressurized zones, local depressurized zones, and stress concentration zones. The maximum vertical stress in the stress concentration zone reaches 102 MPa, with a significant decrease in permeability. Prior to gas management, the maximum coal seam gas pressure was 3 MPa, and the maximum gas content was 16.72 m³/t. Based on stress distribution, permeability, and gas occurrence characteristics, targeted zoning and precise gas management technologies were developed. This resulted in a working face gas precise management model, involving protective layer depressurization, hydraulic flushing, and grid-pattern pre-drainage. In the locally depressurized zone, gas pressure was reduced to 0.18 MPa, and gas content decreased to 2.45 m³/t after pre-drainage through grid-pattern cross-layer drilling. In the stress concentration zone, gas pressure was reduced to 0.15 MPa, and gas content decreased to 2.50 m³/t through hydraulic flushing and grid-pattern cross-layer drilling. No gas exceedance accidents occurred throughout the entire mining period, achieving safe and efficient mining under the stress distribution induced by non-continuous mining. This research holds significant importance in guiding precise gas management in challenging engineering conditions of protruding coal seam groups.