Research and Application of Large-Span Roof Support Technology for Ⅳ Grade Broken Rock Mass

To specifically address the support challenges posed by large-span roofs in Class IV fractured rock masses, a composite support scheme was proposed based on the principles of structural closure, arching effect, and span reduction. The scheme integrates a combination of anchor mesh, shotcrete, prestressed rock bolts, and prestressed anchor cables to achieve comprehensive reinforcement. A non-associated elasto-plastic analysis of the secondary stress field in the surrounding rock was performed based on the Mohr-Coulomb failure criterion. Considering the partitioned boundary conditions, analytical expressions were derived to determine the radii of the loosened zone and the plastic reinforcement zone. The calculated thicknesses of the loosened and plastic zones were 2.53 m and 2.83 m, respectively. Based on these results and relevant engineering standards, the support parameters for the roof were rationally designed. To verify the feasibility of the proposed scheme, a numerical model of Stope #9 was developed using FLAC3D software to simulate three scenarios: no support, the original support design, and the proposed support scheme. Simulation results indicated that the minimum principal stress in the supported roof area under the proposed scheme was reduced to 0~0.25 MPa, which is significantly lower than the tensile strength of the rock. The height of the plastic zone was reduced to 3.6 m, representing a 62.5% decrease compared to the original support design. An industrial-scale trial was subsequently carried out in Stope #9 based on the proposed design and simulation outcomes. During the excavation process, no roof collapse was observed, and the roof exhibited good integrity and stability. These results confirm the rationality and practical feasibility of the proposed support system and provide a valuable reference for similar underground mining projects.