Research on the mechanism and prevention of rock burst in asymmetrical isolated working faces with sawtooth coal pillars

Addressing phenomena such as high stress and high impact risk in asymmetric isolated longwall faces, this study, based on a certain mine's isolated longwall face, employed theoretical analysis, numerical simulation and field practice to investigate the evolution characteristics of the overlying strata in asymmetric isolated longwall faces, clarified the variation law of support pressure under asymmetric constraints, revealed the rockburst mechanism of jagged coal pillar asymmetric isolated longwall faces, and proposed targeted collaborative pressure-relief measures to reduce impact. The results show that when the coal pillar width W₁≤36.5m, the overlying strata form an asymmetric "T" structure; when W₁>36.5m, the overlying strata form a long-arm "F" structure; support pressure on the face displays an inclined "double-peak" distribution from the material gate side to the return gate side; when W₁ increases from 20m to 170m, the peak stress at the ends of the transport and material gates increases by 5.9% and 8.5% respectively, with stress concentration coefficient peaks of 2.20 and 3.05; the degree and range of end stress concentration increase and the strong dynamic load released due to the key layer fracture easily trigger rockbursts on the face. A pre-split roof blasting and large-diameter borehole dynamic pressure-relief scheme was developed to prevent impact, and after construction, microseismic activity intensity and energy density on the face were significantly reduced, lowering the risk of rockburst. The research conclusions can provide reference for the mining of isolated longwall faces under similar conditions.