Abstract: In order to improve the gas permeability of outburst coal seam and solve the problem of gas drainage in low permeability outburst coal seam in China, the relationships between static expansive agent, additional stress and gas permeability were studied theoretically, and the effective stress reduction and gas permeability increase after injecting static expansive agent into the borehole of outburst coal seam were deduced. A comparison of the gas drainage effect parameter of the single hole was made between the zone of expansion and crack and the zone of regular drainage in the M3 outburst coal seam in the right of 1235 working face.The result shows that the gas drainage result is obviously improved by the static expansion and crack in the M3 outburst coal seam, the single hole drainage parameters of the expansion and crack zone is obviously better than the parameters of the drainage hole of the regular drainage zone in the right of 1235 working face, that under this test condition, in the different drilling diameter test scheme which with the same μ, the expansion crack zone increases with the drilling diameter, the single hole gas drainage parameters show an obvious rising trend, mean value of gas drainage flow is 0.104 m³/min and the mean value of gas drainage volume fraction is 63% in the Φ94 mm No.1 drainage hole in the expansion and crack zone, the expansion and crack effect of the drainage hole is the best, compared with the Φ94 mm No.6 drainage hole in the regular drainage zone, the mean values of gas drainage flow and volume fraction is improved by 39% and 15%.

Key words: outburst coal seam, static expansion and cracking, additional stress, gas drainage parameter, gas drainage effect