Study on rational layout of floor gas drainage gateway in high gassy-outburst seam

In order to solve the rapid heading and safe and high efficient mining in the high gassy-outburst seam of Xintian Coal Mine, a floor gas drainage gateway headed along strike direction of the coal mining face was provided. An ultra high hydraulic slotting and permeability improved technology was applied to the gas pre-drainage along the seam gateway. Meanwhile,during the mining period, the seam gateway could be applied as an air return gateway with a Y type ventilation mode. The theoretical calculation of the floor slip line field and the FLAC3D numerical simulation were applied to calculate the floor failure depth and to determine the layer location of the floor gas drainage gateway with a distance of about 14 m to the floor of No.4 seam. The excavation disturbance stress concentration zones of the numerical simulation gateway were within a 5 m scope along the two sidewalls of the gateway. A superposition of the stress concentration zone in the gateway could be avoided. The layout scope of the floor gas drainage gateway was defined. And the total length expression of each borehole raw was established and the best solution was conducted as 125 m. Finally, the horizontal distance to the transportation gateway was determined as about 10 m. The results showed that the hydraulic slotting, pressure released and permeability improvement of the floor gas drainage gateway could realize the 15 days gas drainage target of the transportation gateway. The deformation volume of the roof and floor in the floor gas drainage gateway were about 20 cm and 15 cm and late the gateways were stabilized. Thus，a safety and high efficient mining of the coal mining face could be ensured.