Structural Evolution, seismogenic mechanisms, and control technologies of deep thick-hard roof strata

The combined effects of high static stress, complex key-strata structures, and mining disturbance pose major challenges to deep coal mining. In deep mining, the superposition of high static stress and dynamic loads induced by strata fracturing can trigger high-energy microseismic events, seriously affecting safe and efficient mine production. Taking the frequent high-energy microseismic events during mining of the No. 2215 goaf-side longwall face in Yingpanhao Coal Mine as the engineering background, field microseismic monitoring, theoretical analysis, and engineering verification were combined to investigate the occurrence characteristics of thick-hard key strata and the morphology and evolution of their grouped structures. The spatial distribution, triggering mechanisms, and key influencing factors of high-energy microseismic events were identified, and an integrated control strategy combining mining-speed control, in-roadway blasting, and in-face blasting was proposed. The results show that 54 high-energy microseismic events, defined using an energy threshold of 8.0×10⁴ J, occurred at the No. 2215 longwall face from January to July 2022, of which 41 occurred ahead of the face, accounting for 75.93%. Under double-face mining conditions, the high-position thick-hard roof formed a large-scale “O”-shaped suspended structure, while the low-position roof on the goaf side formed an “S”-shaped or nearly “L”-shaped asymmetric suspended structure. These structures jointly caused concentrations of stress and elastic strain energy within 40–120 m ahead of the face and near the small coal pillar on the goaf side. Sudden increases or decreases in mining speed altered the migration rate of abutment pressure and the rhythm of roof fracturing, and were important triggers of frequent high-energy microseismic events. After implementing mining-speed control, in-roadway blasting, and in-face blasting, the number of 10⁵–10⁶ J events decreased from 20 to 4, representing a reduction of 80.00%, and high-energy microseismic events were effectively controlled.