Study on Bearing Mechanism and Coupling Mechanism of Steel Arch-concrete Composite Structure of Initial Support System of Large Section Tunnel

Fully utilizing and developing underground space is an important direction of future world development. In order to meet the increasing traffic demand, there are more and more super-large section tunnel projects such as two-way eight-lane tunnel. In the initial support system of NATM, “steel arch + concrete shotcrete” is widely used in engineering as one of the most common forms of support. But at present, in the study of supporting system, most researches are based on mechanical analysis of single steel arch, and few of them consider the spatial combination of multi-arch and the influence of concrete shotcrete. Therefore, in order to grasp the spatial combination effect of multi-arch and the influence of concrete shotcrete layer on the bearing mechanism of initial support system, and to establish the analysis and calculation model of initial support system, this paper carries out numerical tests on the mechanical characteristics of three composite steel arch + concrete shotcrete initial support system, and clarifies the spatial combination effect of multi-arch and the effect of concrete shotcrete on initial support. Based on the bearing capacity of the initial support system, the influence of concrete shotcrete strength, arch spacing and longitudinal connection spacing on the mechanical properties of the initial support system is comprehensively analyzed. The research results can provide theoretical basis for the design and application of related engineering.