As the demand for transportation increases in China，more and more highway tunnels adopt the form of super-large section.However，there is still a lack of clear guidance for the design and construction of super-large section tunnels with four lanes or more in the current highway tunnel specifications. There is still a need for in-depth research on the section shape，construction methods，and construction mechanics of super-large section tunnels. Existing research indicates that the use of the benching method for excavation construction of super-large section tunnels is feasible. To obtain the optimized schemes for bench length and anchor rod spacing，numerical simulation was performed in this study to investigate seven different scenarios based on the upper and lower bench construction sections of a certain super-large section flat structure tunnel.The scenarios included bench lengths of 30 m，40 m，50 m，and 60 m，as well as anchor rod longitudinal spacings of 1.0 m，1.5 m，and 2.0 m. The distribution patterns of the plastic zone in the surrounding rock mass，the stress of the surrounding rock，and the deformation of the surrounding rock were analyzed.The study results indicate that the overall maximum principal stress around the tunnel shows a trend of “arch foot>arch waist>arch crown”.An increase in bench length or anchor rod spacing leads to a significant increase in the maximum principal stress at the arch crown. Overall，the settlement and horizontal convergence values of the tunnel arch crowns increase with the increase in bench length. An increase in anchor rod spacing requires other support structures in the initial support to exert stronger control over surrounding rock deformation，potentially leading to the destruction of the support structure. Based on the numerical results and on-site monitoring data，considering factors such as construction efficiency and rock stability，the optimized scheme with a bench length of 50 m and an anchor rod spacing of 1 m was applied in the construction site.The results of this research has high reference value for the optimal selection of excavation and support parameters for super-large section flat structure tunnels.

http://www.goldsci.ac.cn/article/2024/1005-2518/1005-2518-2024-32-2-330.shtml