Study on control technology of gas overrun inmining face of contiguous seams

In order to prevent the gas overrun in the mining process of contiguous seams, the gas overrun mechanism was analyzed by the pore structure and adsorption capacity test of the coal in Songzao mining area of Chongqing.On-site tests were conducted to compare the effect of preventing gas overrun by the following three methods: high-level drainage borehole, high-level drainage roadway and gob drainage borehole.The results showed that the coal pores and fissures are not developed and the permeability is low,the gas pre-drainage effect is poor, and the mining pressure relief causes gas overrun.With the method of high level drainage roadway in fractured zone, the average amount of gas drainage was 12.6 m3/min and average gas concentration was 32.75%, which was 5 times and 2.8 times higher than that of the high-level drainage borehole method. The drainage hole in the gob is connected with the falling belt, which causes the working face air to enter the high level drainage roadway. The average gas drainage concentration is thus reduced to 28.19%, and the drainage volume is 11.38 m3/d.The high level drainage roadway method reduce the average gas concentration in the tail of the working face by 63.2%, and the average concentration of the gas in the corner are reduced by 19.6%. This prevented the occurrence of gas overrun accidents on the working face, and the average efficiency of single-month working face increased by 46.7%. The total drainage of direct usable gas in ten months reached 4.417 million m3, and achieved good economic and social benefits.