Gas drainage optimization via fracture network characterization in coal mining

The collapse of overlying strata in the goaf creates fractures that facilitate gas migration and accumulation in the upper corner, increasing the risk of gas overlimit. This study used physical simulations to analyze the distribution of the “three vertical zones” in the 11308 working face. The caved zone height is 28.5 m, and the fractured zone height is 54.4 m. The “voussoir beam” structure of mining-induced fractures was identified as the primary gas migration channel. An innovative fracture classification method was proposed to clarify their development and distribution, revealing that the low-level “rectangular terrace” acts as a gas accumulation “sweet spot,” guiding borehole extraction. Numerical simulations indicated that gas mainly accumulates in the high-level of the fracture zone (7–10 times the mining height). Based on these findings, a “low-level interception-high-level extraction” directional long borehole layout was designed, along with a dynamic balance model of “airflow-borehole extraction-gas migration.” Field application in the 11308 working face showed a 123% increase in gas extraction and a stable gas concentration of 0.08% in the upper corner, significantly reducing the risk of upper corner gas exceeding the limit. These results provide valuable guidance for managing gas risks in similar geological conditions in coal mines.