Gas Drainage Technology of Mining Fractured Zone in High Gassy and Contiguous Seams

In order to solve gas content over limit problem occurred in a coal mining process of high gassy and contiguous seams, a theoretical analysis and numer ical analysis combined method was applied to analyse the mining cracking evolution law of No.4 seam mining in the south wing of Shaqu Mine and the rational layout of the high level cracking drill hole group was determined.The results showed that a roof falling zone and a cracking zone in the goaf were 8 m and 36.5 m in height indivi dually, there was a vertical height of 8 ~ 23 m from the cracking zone connected to the roof of coal mining face.There was a vertical height of 23 ~ 42 m from a cracking zone no connection to the roof of the coal mining face. The cracks was closely distributed and the complete structure of overburden strata were relative stable in the roo f about 22 m above the coal mining face.A drill hole expanded to this region would effectively improve the concentration of the gas drainage, increase the drainage qua ntity and have a stable gas drainage operation.The site practices showed that with the application of a DDR-1200 mode over 1 000 m directional drilling equipment, drill ing holes were made about 22 m above the coal mining face. The gas drainage effect was remarkable, the average concentration of the gas drained was 90.68%, the av erage pure volume was 11 .58 m3/min.