Determination Method of Drainage Radius of Pre-draining Boreholes Based on Standard Evaluation of Drainage Capacity

In view of the problem of poor practicability of the existing method for measuring the effective drainage radius of coal seam, especially the problem of high sealing requirement in the pressure drop method, a new method is proposed to determine the extraction radius based on the extraction time required by the extraction standard. Through the test of the variation of the gas extraction volume with the extraction time, the total extraction time is determined and the extraction time of different extraction intervals is obtained. Finally, the reasonable extraction distance is determined, and the present field test is carried out in the coal mine of Zhengzhu Coal Mine. Field tests showed that the pre-pumping time of drainage distance of group 2 m, group 3 m and group 4 m were 236 d, 260 d and 273 d respectively. According to the fitting formula between the spacing of the extraction boreholes and the time of pumping and the standard time, when the design time is 240 days, the effective extraction radius is 1 m.