Research on load reduction and rockburst prevention technology in areas with square composite structures of extra-thick coal seams under strong impact

To reveal the impact risk when mining advances into special areas of strong-impact extra-thick coal seams and to enhance rockburst prevention safety during the mining process, the square composite structure area of the 401106 working face at Hujiahe Mine was taken as the engineering background. Through a combination of theoretical analysis and field measurements, the spatiotemporal evolution characteristics of microseismic events in the square composite structure area were investigated, and the mechanism of rockburst induction was explained. It was found that the load concentration in the square composite structure area was relatively high, with a significant increase in both the frequency and energy of microseismic events. Coal-rock fractures were more developed, and microseismic activities were more intense compared to conventional areas. The average maximum energy and energy released per meter of microseismic events increased by 20.1% and 26.3%, respectively, and exhibited a parabolic distribution. Under the combined effects of the square structure effect, tectonic forces, hard overlying strata, and adjacent goafs, the impact risk of the coal-rock mass increased. Based on the principle of "source separation and classified prevention", a "regional + local" load reduction and rockburst prevention technology was proposed. Specifically, for hard overlying strata that generated dynamic and static load sources, a coordinated prevention and control approach using underground long-hole regional hydraulic fracturing and roof pre-split blasting technologies was applied. For the coal body in the square composite structure area, which accumulated static load sources, side and floor destress blasting techniques were used. These measures reduced the periodic weighting step and dynamic load factor, improved the overall stability of the surrounding rock, and enhanced safety during mining operations.