Gas control technology of ground drilling extraction in fully-mechanized caving face of extra thick coal seam

According to the double disasters of the gas and coal spontaneous combustion in a top coal caving mining face with small coal pillars in ultra thick seam of a coal mine in Shanxi Province,with an analysis on the disaster and control methods of the coal mining face,a construction technology to change the surface borehole was provided.Meanwhile,the control methods of the gas drainage from the crack zone and roof falling zone were provided.A microseismic technology was applied to divide the fracture zone of the coal mining face.The optimum gas drainage location of the surface borehole was determined.The results showed that the optimum gas drainage distance of the surface boreholes was about two periodic strata weighting spans of the coal mining face.But the gas drainage scope of the surface boreholes would be imbalance and the distance of the hysteresis effect was 3.3 times of the advance effect distance.The importance of the high distinguishing and low pressure gas drainage system was proved.Under the same condition of treatment effect,taking DN300 ground drilling as an example,the construction speed is eight times that of rock roadway excavation,the construction cost is 1/26,ground drilling has obvious advantages.