Gas drainage technology with high level borehole at coal mining face in gassy thin seam

In order to solve gas emission problem occurred in adjacent seams and goaf of coal mining face in gassy thin seam, based on moving failure law of overbur den strata in goaf,high level boreholes in roof of No.4 seam were applied to gas drainage to release gas pressure. A study was conducted on borehole initial drilling locatio n,borehole final location,borehole final height,distances between boreholes drilled and other gas drainage parameters. In combination with analysis on gas drainage effect of high level boreholes,crack zone height in roof of No.4 seam obtained was about 12 m,the first roof weighting distance of No.401 coal mining face was 20 ~ 30 m," O" ri ng edge width of coal mining face was about 30 m and space between opening boreholes of each high level borehole group would suitable be 8 ~ 12 m. The site applicatio n results showed that with high level boreholes with rational designed construction parameters in crack zone of goaf,drained gas pure volume of single borehole was 0. 01 ~ 0.24 m3/ min,gas concentration at top corner was reduced from previous 0. 89% to about 0. 31%,gas concentration of return airway in coal mining face was reduced fro m previous 0. 65% to about 0.20% and gas over limit occurred in return airway and top corner of coal mining face was eliminated.