Zonal load transfer controlled by an L-shaped irregular coal pillar and the mechanism of rockburst induced by...

Under the condition of slicing mining in extra-thick coal seams, the presence of irregular coal pillars is likely to cause stress redistribution in the roadway region and induce rockburst. Taking the "3·22" rockburst event that occurred in the haulage roadway of the 250,101-2 working face in Huating Coal Mine as the engineering background, this paper investigated the occurrence mechanism of roadway rockburst under irregular coal pillar conditions by combining source mechanism inversion, numerical simulation, and theoretical analysis. The results show that the double-couple component is dominant in the moment tensor inversion results, indicating that the source type of this event was shear-type, and that the essence of the rockburst instability was the sudden shear slip of the coal-rock mass under high-stress conditions. The PFC simulation results show that, under the control of an L-shaped irregular coal pillar formed by a 20 m residual section pillar and a 34 m residual pillar, the overburden load developed a zonal load transfer pattern. Specifically, the 20 m pillar constituted the main load transfer channel, while the compacted zone above the 34 m pillar regained a certain bearing capacity after compaction of the caved rock mass and exerted an auxiliary reloading effect on the underlying surrounding rock, resulting in the haulage roadway not being in a fully destressed state. On this basis, a two-segment bearing model of the L-shaped irregular coal pillar was established, and the static stress distribution characteristics in the roadway region under the combined action of the two-segment loads were analyzed based on half-plane elasticity theory. Furthermore, by incorporating the attenuation law of vibration waves, a stress increment estimation model under dynamic loading disturbance was established, and the dynamic stress increment generated on the roadway surface by the "3·22" rockburst event was calculated to be about 4.06 MPa. Finally, the stress concentration characteristics and stress deflection effect under the control of the L-shaped coal pillar structure were discussed. The results show that an increase in the right-wing thickness of the L-shaped coal pillar structure enlarges the stress deflection zone and enhances stress redistribution toward the roadway, thereby increasing the possibility of rockburst under the combined action of high static stress and dynamic disturbance. The research results reveal the occurrence mechanism of roadway rockburst under L-shaped irregular coal pillar conditions, and can provide a theoretical reference for identifying rockburst hazard zones and optimizing working face layout parameters under similar engineering conditions.