The Initial Support Mechanism Of Long-span Tunnel And The Influence Of Tunnel Construction On Its Mechanical Characteristics

The paper relies on the tunnel project of Chongqing city rail transit route crossing,based on the combination of theoretical analysis,numerical simulation and field measurement,analyzes the mechanical principle of the initial support(anchor,sprayed concrete,steel support)and the surrounding rock.Combined with the actual engineering case,the influence of the construction of the small span tunnel on the stress and strain characteristics of the initial support is studied.The main research contents and achievements are as follows:(1)Study on the mechanism of all-stick bolts in the initial support of long-span tunnels Based on the theory of tunnel surrounding rock deformation and the theory of anchor neutrality,the interaction mechanism between bolt and surrounding rock in large span tunnel is studied.It is found that there are significant differences in the displacement distribution pattern between the arch and the side wall of the large span tunnel,which leads to the different role of the bolt at different positions of the tunnel.Based on the finite element analysis and the theoretical derivation,the design parameters of the bolt in the cross section of the long-span tunnel are put forward.(2)The research on the supporting mechanism of the shotcrete with the support of the long-span tunnel is carried out.The effect of the shotcrete in the initial support is analyzed by using the curved beam as the elastic foundation curved beam structure and the elastic foundation rock theory.Based on the analysis of the mechanical characteristics of shotcrete,the internal force analysis formula of shotcrete structure is deduced by measuring the contact stress of tunneling concrete and surrounding rock.(3)This paper studies the mechanism of steel support in the early support of longspan tunnel,analyzes the characteristics and force characteristics of the combined support of tunnel steel support and shotcrete,and establishes the foundation rock beam with initial support for steel support and shotcrete Mechanics model,the elastic foundation rock beam theory is used to calculate the internal support value of the steel support value obtained by on-site monitoring.The final formula of the long-span tunnel is solved by using the formula.(4)The research on the mechanical properties of the initial support of the long-span tunnel is carried out,and the three-dimensional finite element model is established to analyze the large-span tunnel and the small-distance tunnel.Under different height difference,And the influence of the bending moment,the shear force and the axial force of the shotcrete on the initial support structure of the super-large span tunnel are studied.