Arching Characteristics of a Raw-Coal Bunker and Local Failure Mechanism and Blockage-Removal Parameters of High-Pressure Water Jets

Stable arching and blockage can occur in raw-coal bunkers containing high-moisture coal. Taking the surface raw-coal bunker at the Panxi Coal Mine as an engineering case, this study adopts a sequential multi-method framework. The DEM, CFD, and SPH are used separately to investigate bunker arching and local destabilization, water-jet propagation and attenuation, and the initial dynamic failure of coal, while field tests assess the engineering feasibility of a blockage-removal procedure combining mechanical drilling and high-pressure water jets. The results show that increased moisture content enhances interparticle friction and adhesion. At 15% moisture content, stable coal arches form mainly about 3–5 m above the discharge outlet. Among the disturbance cases examined, a nominal disturbance radius of 500 mm markedly disrupts the arch load-bearing structure and restores discharge. Among the eight water-jet operating combinations investigated, 46 MPa, a total system flow rate of 44 L/min, and a nozzle diameter of 1.14 mm provide relatively favorable axial propagation, with a nozzle-exit velocity of approximately 303.3 m/s and a centerline dynamic pressure of approximately 38 Mpa at 500 mm. Under the adopted coal parameters and initial millisecond-scale impact conditions, SPH predicts a local failure sequence of surface impact, axial erosion, radial crack propagation, and fractured-zone enlargement. A reference velocity of 300 m/s is used in the incidence-angle analysis, for which angles of 60–90° produce relatively favorable local failure. The main coal arch observed in the field is approximately 3.7 m above the outlet, broadly consistent with the DEM prediction. The combined drilling-assisted high-pressure water-jet procedure, using a 45 Mpa, 44 L/min pump, ultimately restores discharge and releases approximately 1841 t of raw coal.