Study on time effectiveness of gas drainage by crossing layer drilling in floor rock roadway with one hole and multi-purpose

In order to To improve the utilization rate of cross-layer boreholes, based on the evolution law of mining fracture field and stress field under the dynamic behavior of coal and rock, a multi-application gas drainage technology with one hole in floor rock roadway with full life cycle was proposed. It can realize the functions of pre-draining coal seam gas before mining, draining coal seam gas during mining,and draining coal seam gas from goaf. Taking the 1604 fully-mechanized mining face of Guhanshan Mine as an example,field tests have been carried out and the results show that:the gas drainage effect of one hole multi-application test drilling hole has obvious timelines characteristics.In order to To analyze the timelines effect law of test boreholes qualitatively and quantitatively, the whole life cycle of gas drainage can be divided into seven stages, namely, initial pre-draining period, high-efficiency pre-draining period, rapid attenuation pre-draining period, high-efficiency pressure relief and flow increase period, low flow depletion period, after mining gas volume recovery period,and after mining gas volume decline flow period. High efficiency pre-draining period is the most critical stage in the whole life cycle, the second stage is the high-efficiency pressure relief and flow increasing period, and the average gas drainage volume can reach 61.4% of the average gas drainage volume in the pre-drainage high-efficiency period. The range from 70 m in front of the working face to 40 m behind the working face is the area affected by mining pressure relief. In the range of 35 to 40 m in front of the working face, the concentration and volume of gas drainage reached the peak. In the stage of mining while pumping, the average gas drainage volume capacity of the test boreholes 20 to 70 m in front of the mining face is 5 times higher than that before pressure relief. In Guhanshan Mine, the reasonable pre-draining period is 260 d, the reasonable drainage while mining period is 46 d, and the reasonable goaf gas drainage period is 26 d. Through a multi- application drill hole in the rock roadway at the bottom of the coal seam to drainage coal seam gas, the goal of reaching the pre-drainage standard and reducing the gas emission from the working face was realized, which has good popularization and application value.