Research on Gas Control Technology of “U+ Omni-Directional Roof to Large-Diameter High-Level Drilling Hole” at the End Mining Face of Multi-Source Goaf

Aiming at the gas over-run problem in upper corner of “U-type ventilation” end-mining working face multi-source goaf #15 coal seam Phoenix Mountain Mine, site survey and numerical simulation methods were adopted, which showed that maximum caving zone height is 14.87 m, fissure 51.63 m. On this basis, control scheme “U+ omni-directional large-diameter high-level borehole along roof strike” was formulated. After adopting scheme, extracted concentration each will reach 5–20%, extraction flow rate 1 m3/min–2.5 m3/min, be controlled below 0.54%, return airway 0.35%, achieving expected effect control.