Deformation and failure laws of surrounding rock in branch roadways of backfill mining faces in coal mines

To explore the spatiotemporal evolution law of surrounding rock deformation and failure in the branch roadway of a working face during backfill mining, this paper takes the 1# backfill working face of a certain mine in Lu'an mining area of Lu'an Group as the research background. A numerical model including the backfill mining working face and its surrounding rock was established using FLAC^3D software to simulate the processes of gateway and branch roadway mining, floor pulling, and backfilling. Combined with on-site displacement monitoring, the deformation characteristics and deformation amounts of the branch roadway during each service stage of backfill mining were analyzed, and further research was conducted on the law of surrounding rock deformation and failure during the branch roadway mining process. The results show that after the gateway excavation, the maximum vertical displacement of the surrounding rock in the roadway is 32.2 mm, and the horizontal displacement is 70.2 mm. The plastic zone failure depth reaches 1.5 m in the roof, 4.0 m in the floor, and 2.0 m in the two sides. The early stage of floor pulling in the branch roadway has a significant impact on the convergence deformation of the surrounding rock on both sides. After the first round of branch roadway mining, the maximum vertical displacement is 95.0 mm, and the horizontal displacement is 83.0 mm; the plastic zone failure depth is 2.0 m in the roof, 2.0 m in the floor, and 5.0 m in the two sides. During the floor pulling process of the 22# branch roadway in the second round, the first 80 meters of floor pulling have the greatest impact on the convergence deformation of the surrounding rock on both sides, and the maximum convergence deformation of the surrounding rock on both sides after floor pulling is 100.9 mm. In on-site monitoring, as the floor pulling progresses, the deformation of the surrounding rock in the branch roadway is relatively concentrated in the 20～90 m section of the branch roadway, with the maximum deformation amount reaching 90 mm, which is consistent with the numerical simulation results.