Roof-blasting control technology for rockburst prevention in the final mining stage with composite hard roof

Under the conditions of a composite hard roof, the risk of rockburst at the end of the working face is significantly elevated due to the coupled effects of coordinated fracturing of overlying hard strata, high-stress concentration in isolated coal bodies, and the presence of wide protective coal pillars in the retreating roadway. Analyses indicate that frequent high-energy microseismic events induced by roof fracturing, along with stress concentration in isolated coal pillars, are the primary triggers of rockburst. Through theoretical analysis and field monitoring, the mechanism of roof-blasting-based rockburst mitigation has been elucidated, and a roof blasting control strategy has been proposed to interrupt stress transmission pathways in critical overlying strata, thereby providing effective protection for retreating roadways and isolated coal bodies. Numerical simulations were conducted to compare the stress evolution and plastic zone distribution in the surrounding rock under three scenarios: no blasting, high-position single-hole blasting, and combined “high + low-position” blasting. The results demonstrate that roof blasting substantially mitigates the effects of stress concentration during the end-of-face stage, with the “high + low-position” combined blasting exhibiting optimal performance by achieving the greatest reduction in peak stress and a notable contraction of the plastic zone. Parameter optimization indicates that a combination of high-position (53 m) and low-position (33 m) hole depths, initiation heights of 19.3 m (high) and 13.0 m (low), and inclinations of 60°(high) and 40°(low) simultaneously enables optimal evolution of plastic failure in the strata and effective stress reduction in coal pillars. Field applications have shown that the peak and concentration of support pressures were significantly decreased, with the maximum monitored coal body stress reaching only 12.7 MPa and exhibiting smooth stress variation. Additionally, the frequency and cumulative energy of high-energy microseismic events were reduced by 30% and 35%, respectively, with no events exceeding 10⁴ J. Multi-parameter monitoring confirmed that the proposed approach effectively improved the stress environment during the end-of-face stage, reduced dynamic load intensity, and achieved coordinated protection of retreating roadways and isolated coal bodies.