Application & research on hydraulic fracturing and cutting top pressure relief technology in large mining height retained roadway

In view of the characteristics of the fifth panel of Sihe coal mine, such as the repeatedly strong mining effects, small size of coal pillars, long service period and high degree of stress concentration in the axis of the syncline, the stress state of surrounding rock was improved by hydraulic fracturing cutting and unloading technology. It improves the stress state of the surrounding rock and provides a new way for the surrounding rock deformation control of the large mining height roadway. The nature of hydraulic fracturing cutting and unloading technology in large mining height retaining roadway was studied. A “quasi-fracture surface” was formed in the overburden of the coal pillar using the high pressure water before the working face is recovered. While the working face is mined, the gob roof broke along "the quasi fracture surface" under the influence of periodic weighting, which reduces the span of the cantilever beam and transferred the high stress of the lateral cantilever beam to the retaining coal pillar. Considering a number of influencing factors such as narrow underground working space, high working face drilling, and ground L-type drainage wells, the hydraulic fracturing topping pressure relief scheme was proposed. The fractured borehole is arranged on both sides, and the deep hole length is 40 m. The shallow hole length is 32 m. In order to ensure the fracturing effect, the fracturing construction is carried out on the front working face 50～100 m, and the reverse fracturing is separated by 2～3 m. Through monitoring and analyzing the pressure relief effect of hydraulic fracturing and cutting, it is concluded that the crack initiation pressure of the roof rock layer is about 24 MPa and the expansion pressure is 21～23 MPa. After the topping is relieved, the amount of movement of the two ribs is reduced by 53%, the amount of roof sag is reduced by 33%, and the amount of bottom drum is reduced by 18%. At the same time, the magnitude of the force change of the anchor cable is significantly reduced. After the fracturing, the vertical stress of the coal pillars peaks from 50 m in the leading working face to 50 m in the lagging working face. The peak point of the vertical stress of the unfractured coal column appears in the range of 150 m to 350 m on the lagging working face.