Study on fracturing timing of hydraulic fracturing top-cutting and pressure relief in roadway with strong dynamic pressure

Hydraulic fracturing technology has been used more in the project of strong dynamic pressure roadway in recent years.In the process of hydraulic fracturing top-cutting and pressure relief in the roadway with strong dynamic pressure, the fracture propagation direction is finally consistent with the direction of maximum principal stress, and the magnitude and direction of maximum principal stress will be changed by the influence of advanced stress in the working face.How to keep the final crack direction consistent with the roadway axis is the key to ensure the effect of pressure relief.In this paper, the 3 D stress evolution law of roof with the advance of working face is measured and analyzed in the 3310 Return Air Roadway of Wangpo Coal Mine, China, by using the improved hollow inclusion stress meter with full bore grouting and anchoring.The results show that the relative value of principal stress at the roof 15 m above the coal pillar is influenced by mining at the distance of 250 m from the working face, and the azimuth and inclination of 3 D principal stress are adjusted at the distance of 200 m from the working face.The relative principal stress value at the roof above 15 m of the working face begins to be influenced by mining at 252 m from the working face, and the azimuth and inclination of 3 D principal stress are basically adjusted at 180 m from the working face, due to the influence of mined-out area, the azimuth gradually appears counter-clockwise deflection within 50 m from the working face.The relative principal stress of the roof above the roadway begins to be influenced by mining at 164 m from the working face, and the closer the relative principal stress is to the working face, the more significant the influence is, especially within 57 m from the working face.The azimuth angle and inclination of 3 D principal stress have been adjusted at the distance of 140 m from the working face, and the angle between σ₁ azimuth and the axial direction of the roadway is smaller between 140 m and 80 m, and is 13°-20°,which is the best time for hydraulic fracturing.At the same time, it does not affect the advance support installation at the mining roadway.