EFFECTS OF MAIN ROOF FRACTURING ON ENERGY EVOLUTION DURING THE EXTRACTION OF THICK COAL SEEMS IN DEEP LONGWALL FACES

摘要

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.