During the extraction of coal from thick seams in deep longwall faces, both high in-situ stress and a massive main roof are common. The progressive fracturing in this massive main roof leads to an increase in the front abutment stress and changes in the strain energy of the coal seam which can lead to dynamic disasters such as rockbursts. Based on the mining conditions observed in Panel 5301 of the Xinhe Coal Mine, microseismic (MS) and borehole stress monitoring, along with numerical simulations, was used to propose an evolution law for coal mine roof fracture, front abutment stress, and strain energy. Results indicate that as the roof collapses during the progress of extraction, the transmission point for overburden load moves forward such that the peak front abutment stress advances to 20–25 m in front of the working face. The coal mass within 22–90 m in front of the working face was observed to accumulate 176.2 kJ of strain energy, with the peak strain energy increasing from 80.15 kJ to 136 kJ. The data collected and analyzed in this research provides a theoretical basis for forecasting the location of mining-induced rockburst based on observed fracturing in the main roof.
Using the FLAC3D numerical simulation method, the characteristics of mining stress evolution, fault activation patterns, and fault energy evolution characteristics are simulated and analyzed in the process of the footwall and hanging wall working face heading to a normal fault. The study shows that the fault cut off the mining stress propagation of overlying strata, and the stress blocking effect due to the fault is evident. When working faces head towards a fault, the abutment pressure and the vertical stress of the surrounding rock increase first and subsequently decrease. The abutment pressure of the coal wall and fault is highest when the distances to the fault are 40 m and 30 m for the footwall and hanging wall working faces, respectively. Moreover, the hanging wall mining stress is higher than the footwall mining stress. Fault activation in high-located strata precedes that in low-located strata when working faces head towards the normal fault. Energy is gradually accumulated before unstable fault events take place because of mining, and fault instability quickly releases a lot of energy. The mining stress concentration and fault activation due to faults easily result in rock bursts and mine seismicity, Wu Quan-sen, Jiang Li-shuai and Wu Quan-lin., and Obsahuje bibliografické odkazy