Study on the Co-Evolution Mechanism of Key Strata and Mining Fissure in Shallow Coal Seam Mining

Shallow coal seam mining makes the evolution form of mining fissures in rock and soil layers diversified, which leads to the easy penetration of mining fissures as the main channel of water, sand inrush, and air leakage. In order to reveal the co-evolution mechanism of broken rock beam structure and mining fissures in key strata, taking Hanjiawan Coal Mine as the research background, the relationship between mining fissures and rock beam structure, fissure activation period, propagation characteristics, and connectivity of working face was studied by means of field observation, physical similarity simulation, and theoretical derivation. The research shows that the fracture structure of key strata in shallow coal seam mining mainly includes hinged rock beam and step rock beam structures. Through the analysis of the rock beam structure, we found that the types of mining fissures in the overlying strata of key strata were up and down I-I and I-II mining fissures, and the heights of fissure development were 44.38 m and 98.35 m, respectively. The key block rotation made the mining fissures undergo five dynamic activation processes. The calculation formula of the fissure activation cycle was established, and the rock breaking angle, mining fracture lag distance, and fissure penetration discriminant were obtained and verified by field measurement results.