Underground directional hydraulic fracturing of near-field hard roof in coal mines: rockburst prevention mechanism

To address the unclear rockburst prevention mechanism of underground directional hydraulic fracturing (UDHF) in the near-field hard roof, this study was conducted based on the hard roof working face of the MC Coal Mine. Using numerical and theoretical models of UDHF, it analyzed the characteristics of overburden movement, fracture development, structural fracture, and stress evolution in the stope, discussed the rockburst prevention mechanism, and carried out field test. Key fndings include: (1) The increments of rock fractures and displacement are significant, with growth rates gradually decreasing upward from the fracturing-controlled area and peak growth rates of 414% and 178%, respectively. (2) The length of the cantilever bearing structure of inferior key stratum -1 decreases by 34.3 m, a reduction of 73.4%; the front abutment pressure peak decreases by an average of 3.13 MPa, a reduction of 8.4%. (3) After the main key stratum fractures, the distance from the peak point to the working face is reduced by 3.87 m, a reduction of 24.2%; the distance by which the stress recovery point in the goaf lags behind the working face is reduced by 23.5 m, a reduction of 14.9%. (4) After field fracturing, the peak and average Er values of the rock strata increase by 52.3% and 34.6%, respectively; the frequency of hazardous microseismic events decreases by 30.1%. UDHF can reduce the rockburst risk in the stope by controlling the movement and fracture modes of rock strata. Therefore, it can be widely used for near-field hard-roof rockburst prevention.