Application of hydraulic fracturing pressure relief technology in surrounding rock control of double-U roadway retaining

Due to the influence of many disturbances in the process of retaining the roadway outside the double U layout working face, taking 2502 working face of Zhangcun Coal Mine of Lu’an Group as the engineering background, the field tests of directional hydraulic fracturing technology for single row of fracturing boreholes with different spacings were designed and carried out, and the influence of drilling spacing on fracturing effect was explored. In the tests, four reasonable fracturing sections were set for each borehole, and the fracturing was carried out step by step from the bottom to the opening of the borehole, which effectively solved the problem of hard roof rock hanging and difficult to span. The results of field tests proved that directional hydraulic fracturing forms cracks in roadway roof rock, which weakens the strength of local surrounding rock, abates the stress concentration of roadway roof and reduces working resistance of the end bracket effectively. The density of borehole has a small influence on the unloading effect of shallow surrounding rock, but it has a big impact on deep surrounding rock. The pressure relief effect of roadway is increased by 53% after drilling density increased by 3 times, and comprehensive comparative analysis shows that the drilling spacing of 14 m is the most economical and reasonable under certain conditions. After directional hydraulic fracturing, the displacement of roadway roof and floor and two sides is decreased by 45% and 26% respectively, which has good effect on controlling roadway deformation.