1.Mine Safety Technology Branch,China Coal Research Institute,Beijing ,China;2.State Key Laboratory of Coal Mining and Clean Utilization,Beijing ,China;3.College of Mining,Liaoning Technical University,Fuxin ,China

This paper is devoted to improve the efficiency of gob gas drainage using directional high-level boreholes in Chengzhuang mine.The evolution and development range of roof cracks are studied using both theoretical calculation and numerical simulation. The gas drainage efficiency and gas control effect are studied when the high-level boreholes are placed at different layers of the fracture zone to determine the best horizontal location of the high level borehole.The results show that the caving and fissure development of roof strata are arch distributed and the fracture zone is between 21.90 and 62.54 m. When the high-level boreholes are located 45 m away from the roof of the coal seam, the high concentration gas can be extracted efficiently while the gas in the upper corner can be well controlled. The concentration and purity of gas extraction can be maintained at a high level for a long period of time after the directional high-level boreholes are constructed.This gas extraction technology ensures a safe production during mining the working face, which is evidenced by the maximum gas concentration in the upper corner of 0.69%.