Abstract
In order to keep pace with fast urbanization and explosive growth of highway traffic volume in China, more and more super large-span tunnels are constructed or will be constructed in the coming years. It is of great significance to employ a suitable construction method for ensuring construction safety when tunnelling in a complicated geological environment. Based on the reconstruction and expansion project of Binlai in China, this paper aims at studying deformation behaviors and mechanical properties of super large-span and shallow tunnel constructed using the upper-bench CD method. The study results showed that the crown settlement of the pilot tunnel was larger than that of the rear guide tunnel, and the deformation of rock mass tended to be stable after 60 days of excavation. The structural stress changed greatly in the construction stage, the stress distribution of steel rib was mainly under compression, and the maximum compressive stress of shotcrete appeared at the tunnel vault. The supporting structure was always kept in a safe state, and its safety factor was higher than 1.5. However, the upper-bench CD method has poor performance in controlling surface subsidence and horizontal convergence. The study of this paper provides a new construction method and useful reference for similar super large-span tunnels.
Highlights
With the rapid development of national economy and the urgent demand of highway transportation development in China, existing single-hole two-lane highway tunnels can no longer satisfy the transportation needs, resulting in the emergence of double-hole eight-lane tunnels in many new or extension projects, such as Qingxi Tunnel, China Hanjialing Tunnel, and Longtoushan Tunnel [1,2,3]. e excavation spans of double-hole eight-lane tunnels are generally larger than 18 m, which are defined as super large-span tunnels
With the improvement of tunnel construction standard, more attention has been paid to the reasonable construction method of super large-span tunnels in complex geological environment [4,5,6,7,8]
It is still unclear for the mechanical properties and structural safety of super largespan tunnels constructed by the upper-bench CD method in the construction process. erefore, it is necessary to study deformation behaviors and mechanical properties of super large-span tunnels and explore the application scope of the upper-bench CD method based on the Letuan Tunnel in the reconstruction and expansion project of Binlai in China. e deformation data on rock mass and structural stress of supporting structures were obtained through field tests, and the mechanical properties and safety analyses of the supporting structures are performed by numerical simulation
Summary
With the rapid development of national economy and the urgent demand of highway transportation development in China, existing single-hole two-lane highway tunnels can no longer satisfy the transportation needs, resulting in the emergence of double-hole eight-lane tunnels in many new or extension projects, such as Qingxi Tunnel, China Hanjialing Tunnel, and Longtoushan Tunnel [1,2,3]. e excavation spans of double-hole eight-lane tunnels are generally larger than 18 m, which are defined as super large-span tunnels. Compared with traditional CD method, the upper-bench CD method has the advantage of shortening cycle time, which greatly improves construction efficiency and saves the construction cost by reducing temporary support [25]. It is still unclear for the mechanical properties and structural safety of super largespan tunnels constructed by the upper-bench CD method in the construction process. Erefore, it is necessary to study deformation behaviors and mechanical properties of super large-span tunnels and explore the application scope of the upper-bench CD method based on the Letuan Tunnel in the reconstruction and expansion project of Binlai in China. Is study can provide reference for similar engineering construction of super large-span tunnels
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