Analysis of Characteristics of Plastic Zone and Mechanical Properties of Anchor Structure in Hydraulic Tunnels with High Ground Temperature

In order to explore the characteristics of plastic zone and the mechanical properties of anchor structure during the construction of hydraulic tunnels with high ground temperature, the high-temperature section of the diversion tunnel of a hydropower station in Xinjiang was studied. Based on the temperature data and the axial force data of the bolt on-site, the Drucker-Prager constitutive model and the finite element method were adopted to simulate and analyze the temperature-stress coupled field and the initial anchoring support during the construction of the high ground temperature tunnels. The results showed that, after the excavation of the tunnel, a crescent-shaped plastic zone first appeared at the hance, then expanded to the spandrel and vault, and finally formed an irregular ring-shaped plastic zone around the tunnel. The higher the initial temperature of surrounding rocks, the larger the plastic deformation and the range of the plastic zone. When the temperature exceeded 80∘∘C, the plastic zone was more likely to expand to the spandrel and vault; and meanwhile, when the bolt was closer to the hance, the neutral point was closer to the cavity wall. As the stress was released, the neutral point moved from close to the cavity wall to away from the cavity wall. Anchoring support can effectively limit the development of plastic zone in surrounding rocks under high ground temperature. After 10 days of anchoring support at 60∘∘C, 80∘∘C, and 100∘∘C, the range of the plastic zone decreased by 9%, 20%, 24%, respectively, and the maximum axial force of a single bolt was 19.4 kN, 20.1 kN, and 23.8 kN, respectively. The higher the temperature, the higher the strength of the bolt.