Research on gas drainage effect in goaf by deephole presplitting

Aiming at the problem of gas overlimit caused by hard roof suspension in goaf of long span working face, taking the geological condition of Luning mine as engineering background, the study on gas control in goaf is carried out by numerical simulation and field test.The results of FLAC^3D simulation show that the initial step distance reaches 60 m when no treatment measures are taken on the roof.Based on the principles of deep hole blasting and high level borehole extraction in goaf, the field test results show that the working surface incline to step distance is out of synchronization after the deep hole presplitting, and the initial step distance is reduced to 31-45 m.After the pressure is applied, the maximum gas drainage concentration and pure flow rate of the high-level drilling hole increased by 1.8 times and 5.6 times.The roof pressure can promote the extraction of high borehole and intubation, but the impact on the high-level drilling is more obvious, and the gas control is mainly based on the extraction after the pressure.