Study on the influence of steel casing backspin construction between parallel tunnels based on DEM-FDM coupling method

This paper adopted a discrete element method (DEM) and finite difference method (FDM) coupled numerical method to study the influence of steel casing backspin construction between parallel tunnels. A numerical model is established according to an field test, and the validation of the numerical analysis method is verified by comparing the simulated value with the measured value. The load and deformation characteristics of tunnel and soil layer under three working conditions, i.e., double tunnel - static pressure, double tunnel - spinning and single tunnel - spinning are analyzed by numerical model. The results indicate that the transverse displacement caused by steel casing spinning condition is 163.5% of the static pressure condition, and the transverse and vertical deformation of single tunnel condition is increased by 32.7% and 53.4%, respectively, compared with that of double tunnel condition. Compared with static pressure condition, spinning can effectively reduce the convergence deformation of segments, and the convergence displacement under single tunnel condition is twice that under double tunnel condition. Under spinning conditions, the rotation index increases first and then decreases with the vertical displacement of the steel casing, and the maximum value occurs near the displacement of the casing to the tunnel arch. Under static pressure conditions, the dislocation of the segment caused by vertical rotation should be focused. For the double tunnel - spinning condition, the stratum displacement caused by soil horizontal displacement in the initial stage of construction should be concerned, and the possible mechanical overturning and the vertical error of steel casing caused by soil vertical displacement in the later stage of construction should be focused. The stress distribution area and characteristics of tunnel segment are closely related to the dynamic construction process of steel casing, and corresponding segment reinforcing measures should be adopted in different stages.