Abstract: The design of underwater tunnel has special requirements for the thickness of the frozen wall. To improve the frozen wall design of the cross-passage in the Maliuzhou waterway section of the Zhuji Intercity Rail Transit Project, based on the fluid-solid coupling theory, the finite difference method is adopted to analyse the stability of the underwater tunnel numerically. By simulating underwater tunnel with different frozen wall thickness, the responses of underwater tunnel stability to the thickness of frozen wall are discussed and the optimizaitons of frozen wall thickness are done. Some findings are as follows. Compared with the non-permeability model, the fluid-solid coupling model has the same distribution of stress on the frozen wall, but the overall values are obvious larger, which means the effect of water cannot be ignored. Due to the existence of water, the frozen wall tends to be “homogeneous”, and the stress concentration phenomenon is alleviated, but the distribution range of high shear stress is expanded, which increases the risk of shear damage; the frozen wall is changed to be under the tension from the pressure, which decrease structural stability. The deformation of the frozen wall is intensified under influence of the fluid-solid coupling and increase with the decreases of the thickness until the thickness of the model reaches 2.0 m or more, where the deformation of the frozen wall is basically stable. The plastic zones of the fluid-solid coupling models mostly exist at the arched areas on both sides, no plastic zone is formed in the models with 3.0 m and 2.5 m thickness, the plastics are formed in the opposite sides of the model with 2.0 m thickness, the plastic zone is almost going through in the models with 1.5m thickness, the damage zone is formed obviously at frozen wall arch of the model with 1.0 m thickness. The thickness of 2.5 m is selected as the optimized thickness of the frozen wall. This optimized thickness is directly applied to the design of the No.4 cross-passage, which is constructed by a freezing method. Through the on-site monitoring test, the validity and the effectiveness of the optimization scheme are verified, which means this optimization scheme has essential promotion and application value for the design of frozen wall thickness in similar projects.

Key words: underwater tunnel, fluid-solid coupling theory, frozen wall, thickness optimization