Analysis of advancing speed effect in gas safety extraction channels and pressure-relief gas extraction

Combined with the coal mining process of a high gas coal mine in Jinzhong, Shanxi Province, this paper discussed the evolution mechanism of the gas safety extraction channels induced by the mining of overburden fissures in the fully mechanized mining working face and carried out the physical similar simulation test. According to the theory of mining fracture elliptic paraboloid zone, the working face advanced speed as the key parameter, mathematical modelling of the gas safety extraction channel profile was performed. The effect of advancing speeds on the evolution of gas safety extraction channels in overburden fissures was comprehensively analysed. The results suggested that increasing advancing speed reduced the height of the caving, fractured and bending zone, enlarged average weighting intervals, and the range of development was small. What's more, with increasing advancing speed, gas safety extraction channels presented gradually reduced bed-separation volume and continuity, and the fractal dimensions (7.0 < 5.0 < 3.0 m/d) also decreased. By conducting on-site high-level drilling field tests, parameters of the high-level boreholes were optimized based on specific advancing speeds, which ensured production safety and efficiency of the mining working face. The present work contributes a theoretical guides for the identification of gas extraction area under different advancing speeds.