Abstract:
In the mining of steeply inclined coal seams with hard roofs, the large dip angle of the coal seam leads to large-scale roof hanging of the hard roof, resulting in elevated clamping stress within the coal and dynamic impact loads from the fracture of thick and hard roofs, which readily triggers rock bursts in steeply inclined coal seams. To achieve regional control of the thick hard suspension plate structure in steeply inclined coal seams, a ground inclined well regional fracturing technology for rockburst prevention was proposed to weaken the impact source and reduce the impact risk. Taking the Wangjiashan Coal Mine in Gansu Province as the engineering background, the paper analyzed historical rock burst incidents and microseismic energy events, the characteristic manifestations of rock burst in steeply inclined coal seams were identified. The evolution of overburden structures and the dynamic load transfer mechanisms in steeply inclined coal seams were investigated, thereby identifying the key stratum for rockburst control. The evolution of stress and energy fields in the coal-rock mass before and after ground fracturing were obtained by simulation. The mechanism of regional weakening and rockburst prevention through ground fracturing in steeply inclined coal seams with thick, hard overburden. The results indicate that steeply inclined hard overburden exhibits significant stress and energy concentration. Under the rotational squeezing effect of its large-scale hanging roof structure, the stress extremes at the "fulcrum" of the low-high level cantilevers reach 26.7 MPa and 28.6 MPa. The regional volumetric fracture network formed through ground inclined well fracturing, disrupts the stress transfer pathway and redirects stress toward deeper coal-rock masses, leading to an improved stress environment in the stope. Following fracturing, the peak stresses in the low-high level hanging roof structures are reduced by 14% and 44%, respectively, while the peak energy values decrease by 10.5% and 20.9%, indicating significant pressure relief and energy release effects. A method for identifying key control layers for ground fracturing has been developed, and a full trajectory equation for ground inclined well was established, and engineering practices were conducted. The results demonstrate that ground fracturing can generate a volumetric fracture network distributed along the dip direction and extended along the strike of the rock layers, with dimensions reaching 400 m×200 m×50 m. The thick hard overburden was regionally fractured, completely eliminating 10
4 J level high-energy events. Seismic computed tomography results further indicate that the velocity anomaly coefficient (
An) in the fractured zone remains below 0.20, corresponding to a stress concentration level rated as medium or lower, and the velocity gradient coefficient (VG) remained below 0.05, confirming an absence of rockburst risk. The research results demonstrate the feasibility of the ground inclined well regional fracturing technology for rockburst prevention. A scientific design methodology for ground inclined well regional fracturing was established, providing an innovative technical approach for rockburst control and improving the existing rock burst prevention and control system in steeply inclined coal seams.