Deformation characteristics and outburst mechanism of coal mass ahead of working faces under dynamic disturbance induced by roof fracturing

Abstract

For working faces in soft coal seams closely (especially directly) overlain by hard rock strata, intense dynamic disturbances induced by roof fracturing not only increase the susceptibility of coal and gas outbursts, but also lower the critical gas threshold for disaster initiation. However‌, existing studies on the outburst mechanisms of such working faces remain insufficient, resulting in low pertinence‌ and poor practical effectiveness of prevention measures. In view of this, systematic study was carried out through numerical simulation and theoretical analysis, with a typical working face as the engineering background. Discrete element software (PFC) was adopted to conduct numerical simulations on the critical process of coal mass deformation and failure under the dynamic disturbance induced by roof fracturing. On this basis, the evolutionary process and initiation conditions of outbursts were analyzed, thereby elucidating the outburst mechanism. The results show that under dynamic disturbance induced by roof fracturing, the coal mass with an approximately triangular cross-section in the upper zone near the working face rib undergoes preferential failure accompanied by more intense damage. Combined with relevant existing research, it can be inferred that dynamic disturbance increases the gas desorption rate and initial expansion energy of coal mass, aggravates the outburst susceptibility and reduces the critical gas threshold for disaster initiation, and this effect is most pronounced in the upper area of the working face. On this basis, engineering implications for the prevention and control of such outbursts are drawn. Key emphasis should be placed on the upper coal zone, which serves as the critical outburst-prone area of the working face. Meanwhile, dynamic stress induced by roof fracturing should be mitigated while implementing gas drainage and static stress relief. Accordingly, a targeted outburst prevention scheme using near-roof boreholes is proposed, and field industrial tests confirm its feasibility and effectiveness. This study provides a theoretical basis and engineering reference for the mechanism understanding and disaster prevention of outbursts at working faces under dynamic disturbance induced by roof fracturing.