Abstract:Under the complex geological conditions of seabed,the pressure on surrounding rock of shallow double-arched tunnel is usually unsymmetrical,especially when the tunnel is connected to land and surrounded by soft rock. Consequently,the stability of the surrounding rock will be affected by the unsymmetrical pressures. In this paper,the pre-support function of pipe shield on unsymmetrical pressure section of double-arched tunnel was analyzed by using three-dimensional elasto-plastic contact finite difference method. The calculation results with different parameters of the pipe shield or tunnels were compared to analyze the effect of pipe shield. The mainly numerical results include:(1) the plastic zone and crown subsidence of the tunnel with/without pipe shield were simulated,respectively;(2) comparison of the deformation and moment of pipe shield according to design parameters or optimized parameters of pipe shield is conducted;and (3) comparison of crown subsidence and horizontal convergence displacement of FEM results with the corresponding item of actual measured results is performed. Pipe shield and grouting-reinforced rock can reduce the plastic zone around tunnel caused by unsymmetrical pressures effectively and it is necessary for double-arched tunnel in soft rock under unsymmetrical pressures to adopt pipe shield pre-support. Unsymmetrical pressures usually bring different stresses to lateral cavities of tunnel and the deformation of surrounding rock is uniform. Unbalanced design should be adopted for pipe shield in order that the deformation and stress can be controlled effectively. The result of numerical simulation is in accordance with the actually measured data,and it is proven that optical design of pipe shield is reasonable.