Engineering application of a load-induced beam-type bearing model for deep water-bearing coal specimens

To investigate the bearing characteristics of deep coal mass under long-term spray-water conditions, this study took the rib coal mass at the head area of the third belt conveyor in a kilometer-deep roadway of the Huainan mining area as the research object, and conducted wave velocity tests, mechanical tests, and acoustic emission monitoring experiments on both dry and water-bearing coal specimens. The results show that although the peak strength of deep coal specimens decreases under water-bearing conditions, the overall continuity and load transfer capacity are enhanced compared with shallower specimens. During loading, larger-scale fracture structures develop internally, ultimately leading to structural instability through tensile opening of the dominant fractures. Based on these experimental phenomena, a load-induced beam-type bearing model applicable to deep water-bearing coal specimens was selected, and the strength formula of the bearing model was calibrated considering parameters such as moisture content and fracture dimensions. The calculated results are close to the experimental data, demonstrating potential for field application. Subsequently, taking the moist coal pillar in a sectional roadway with possible underground fractures as the research object, COMSOL software was further used to simulate the bearing instability and grouting process of the pre-cracked water-bearing coal pillar, and the fracture propagation and slurry diffusion laws under different grouting pressures were analyzed. The simulation results show that the stress concentration at the fracture tip during the initial stage of fracture propagation is close to the calculated value from the formula, which to some extent verifies the engineering applicability of the load-induced beam-type bearing model. The slurry diffusion effect under 2 MPa grouting pressure is better than that under 1 MPa, without inducing dominant fracture propagation or overall coal mass uplift due to excessively high grouting pressure. Based on the above simulation results, field tests were carried out, which effectively alleviated rib spalling and floor heave in the test area. The research findings can provide a reference for surrounding rock control and grouting design in deep water-rich roadways.