Technology feasibility of gas drainage with comb-shaped long borehole in floor instead of translayer borehole

Drainage technology of translayer borehole in floor roadway and directional long hole are the most important gas control measures in high gas and outburst-prone mining face at present. The coal seam in Zhaozhuang mine has the characteristics of being soft and low gas permeability. It is difficult to drill and form holes in a coal seam. For gas control, the major method is to drill a translayer borehole to eliminate gas outburst, supplemented by in-seam gas drainage boreholes. However, there are shortcomings such as large engineering volume, long construction period and high cost of drilling in floor rock roadway. The directional long borehole has technical defects such as uneven drainage and insufficient coverage. In order to compare and investigate the drainage effects of the long borehole and the borehole in the floor rock roadway, the drainage effect of two gas control methods in mining face 1307 was investigated. The results show that under the same mining conditions and coal body range, the total amount of gas extraction by five comb-shaped long boreholes accounted for 75.4% of the total gas drainage of the translayer boreholes through the floor, while the economic input of the comb-shaped long boreholes accounted for only 29.2% of the translayer boreholes in the floor. In the case that the extraction effect is basically the same, the comprehensive economic benefit of the comb-shaped long hole is higher. From this it is concluded that the gas drainage technology of the comb-shaped long boreholes to replace the translayer boreholes is feasible. The study provides a practical reference for the technical feasibility of substitution of the translayer boreholes with comb-shaped boreholes, a more economical and feasible treatment scheme for the gas control in gas outburst-prone coal mines with soft and low permeability coal.