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Analysis of Stress Characteristics and Stability of Initial Support Arch of Tunnels with the Spatial Effect of Truss Structure Taken into Consideration
(China Railway 16th Bureau Group Co., Ltd., Beijing 100018)
Abstract By now, no standard has been established for structural design of initial support of tunnels. During actual construction, selection of the parameters of initial support arch mainly relies on previous construction experience,and the structural calculation often simplifies the arch as an ideal uniaxial member. In order to provide the theoretical basis for fine design of the initial support arch, the common structural forms of initial support arch are gathered in this paper, and the common geometric parameters of three-string and four-string lattice girder and section steel arch are presented. After the relation between crown settlement and surrounding rock pressure is established, the concept of support rigidity of initial support arch is proposed. With the restraining action of arch feet lock adequately considered, the hingeless arch model and two-hinged arch model under the action of uniform centripetal load have been built. The instability mechanism of initial support arch in the two models has been analyzed, and the method to determine the stability factor of hingeless arch and two-hinged arch has been given; it is believed that the critical load can be used as a criterion for determining the stability of arch system. On this basis, how the diagonal web member will affect the compressive stiffness and flexural stiffness of arch in the basic configuration of Pratt type and Warren type lattice girders has been analyzed. As the results suggest, compared with the ideal state, when the shear deformation of lattice unit is considered, the critical load of the support with lattice girder decreases. The mechanical structural model of steel reinforcement with "8"-shaped knot has been built, decompositional projection of the forces on the structure has been conducted, and the methods to calculate the axial compressive stiffness, flexural stiffness and shear stiffness of the crossed lattice unit of chord-free member has been put forth. After numerical simulation and calculation of engineering cases, it is believed that the analytic formula can be used to accurately calculate the destabilization load of support arch and the arch stiffness. The study results are helpful for scientifically understanding the bearing characteristics and stability of initial support of tunnel, and are valuable reference for selection and operation of initial support structure.
Abstract：
By now, no standard has been established for structural design of initial support of tunnels. During actual construction, selection of the parameters of initial support arch mainly relies on previous construction experience,and the structural calculation often simplifies the arch as an ideal uniaxial member. In order to provide the theoretical basis for fine design of the initial support arch, the common structural forms of initial support arch are gathered in this paper, and the common geometric parameters of three-string and four-string lattice girder and section steel arch are presented. After the relation between crown settlement and surrounding rock pressure is established, the concept of support rigidity of initial support arch is proposed. With the restraining action of arch feet lock adequately considered, the hingeless arch model and two-hinged arch model under the action of uniform centripetal load have been built. The instability mechanism of initial support arch in the two models has been analyzed, and the method to determine the stability factor of hingeless arch and two-hinged arch has been given; it is believed that the critical load can be used as a criterion for determining the stability of arch system. On this basis, how the diagonal web member will affect the compressive stiffness and flexural stiffness of arch in the basic configuration of Pratt type and Warren type lattice girders has been analyzed. As the results suggest, compared with the ideal state, when the shear deformation of lattice unit is considered, the critical load of the support with lattice girder decreases. The mechanical structural model of steel reinforcement with "8"-shaped knot has been built, decompositional projection of the forces on the structure has been conducted, and the methods to calculate the axial compressive stiffness, flexural stiffness and shear stiffness of the crossed lattice unit of chord-free member has been put forth. After numerical simulation and calculation of engineering cases, it is believed that the analytic formula can be used to accurately calculate the destabilization load of support arch and the arch stiffness. The study results are helpful for scientifically understanding the bearing characteristics and stability of initial support of tunnel, and are valuable reference for selection and operation of initial support structure.
SUN Yi
.Analysis of Stress Characteristics and Stability of Initial Support Arch of Tunnels with the Spatial Effect of Truss Structure Taken into Consideration[J] MODERN TUNNELLING TECHNOLOGY, 2023,V60(3): 34-43
2023, Vol. 60 