Research on the Mechanism of Rockburst Incubation and Risk Identification in Isolated Working Faces within the Axis Zone of Synclines in Extra-Thick Coal Seams

This study employed an integrated approach combining theoretical analysis, numerical simulation and field monitoring to address the issues of high stress concentration and rockburst risk during the mining of isolated panels within a synclinal axis. This methodology was employed to systematically investigate the evolution of the overburden structure in this geological setting. The spatiotemporal distribution characteristics of mining-induced stresses were clarified, revealing the mechanism of rockburst in isolated panels within extremely thick coal seams in synclinal axes. Based on existing microseismic monitoring, a comprehensive, modified method for identifying rockburst risk was developed and implemented. The results indicate that, when mining the working face in the synclinal axis area, the overburden structure exhibits a long-arm 'F' type characteristic when the minimum pillar width is greater than 36.5 m (95 m in this case). As the working face gradually moved closer to the transport roadway along the synclinal axis, the maximum principal stress peaked at 42.1 MPa, an increase of 29.1% on the initial value of 32.6 MPa, with the corresponding stress concentration factor rising to 2.34. During this process, the combined effect of stress concentration in the front abutment area and the strong dynamic load released by the fracture of the key strata resulted in a substantial decrease, or even a shift towards tensile stress, in the minimum principal stress σ ₃. This enabled the coal-rock mass to fail at a lower maximum principal stress σ ₁, ultimately triggering a rockburst. A multi-indicator microseismic risk identification model was constructed based on the preceding analysis. This model raised the working face's early-warning accuracy from 84.1% to 94.9%, significantly enhancing its rockburst risk identification. The findings can provide a reference for isolated working faces with similar geological and mining conditions.