Optimization of pressure-relief windows in roadway ribs under high stress

At present, research on pressure-relief support for the two ribs of deep high-stress roadways mainly focuses on surrounding rock modification or pressure-relief design of active support components. However, quantitative research on the relationship among "weakening zone size, layout position, stress redistribution, and stability boundary" in passive support surface layers such as steel mesh remains insufficient. To address the above problems, a control scheme involving preset "pressure-relief windows" in the roadway rib support surface layer was proposed. Based on the assumption of an idealized continuous medium, a stress analysis model under the disturbance of rib pressure-relief windows was established, and the influence of pressure-relief window positions on the coordinated control of corner stresses in the roof and floor was discussed. FLAC3D was used to establish a three-dimensional numerical model, and the support surface layer was simulated using the equivalent continuous thin-layer method. Working conditions with different pressure-relief window sizes were simulated by locally deleting thin-layer elements. The results showed that: ① The pressure-relief window size had a critical safety threshold of approximately 0.5 m. When the window size was below this value, the pressure-relief window and surrounding rock maintained a relatively stable coordinated load-bearing structure. When the pressure-relief window size exceeded this value, the central area of the pressure-relief window gradually became dominated by tensile stress, and stress concentration in adjacent non-windowed regions increased significantly. ② The 0.9 m condition showed the strongest stress relief effect, but obvious instability tendencies were observed, and therefore it was not suitable as a recommended engineering size. Based on the theoretical analysis and numerical simulation results, it was concluded that arranging the pressure-relief window in the middle of the roadway rib was more favorable for the coordinated control of corner stresses in the roof and floor. The recommended window size for engineering applications was approximately 0.5 m. Field application results showed that after adopting the pressure-relief window scheme, the overall deformation of the roadway surrounding rock was controlled to a certain extent. The roof separation remained generally small, and no obvious through-going separation or large-scale roof fall was observed. The deformation rate of the two ribs gradually decreased with time, and the roadway surrounding rock gradually became stable.