Directional drilling replacing tailgate gas drainage technology in gassy fully-mechanized coal mining face

In view of the problem of gas overrunat the upper corner under the condition of U-shaped ventilation in gassy fully-mechanized mining face, the necessity and feasibility of directional drilling replacing tailgate drainage and pressure relief are analyzed, and the principle of relieved gas drainageis expounded. With physical simulation and theoretical analysis, the evolution law of mining-induced fracture in mining overburden is analyzed, the directional drilling parameters are determined, and the field engineering application has been carried out. The results show that as the working face advances, the mining face of the test working face forms irregular caving zone, regular caving zone, fracture zone and continuous bending deformation zone in the overburden of the test working face. The height of regular caving zone is 17.9 m (4.48 times of the mining height), and the height of fracture zone is 60.36 m (15.09 times of mining height). The horizontal distance between the directional drilling and the return air roadway is 8～20 m, and the average vertical distance between the drilling and the coal roof is 18.5 m. Directional drilling rig has been used to construct drilling with small offset and accurate positioning. The average gas drainage volume is 6.37 m3/min, accounting for 8.59% of the gas emission. The effect of directional drilling instead of the tailgate gas treatment has been achieved to ensure safe mining in the working face.