Abstract:The unsaturated soil was conceptualized as three-phase medium, which consists of fluid, solid and gas, and the shield tunnel was simplified as an infinite Flügge cylindrical shell. The Helmholtz decomposition theorem was used to solve the governing equations of unsaturated soil and the separation-of-variable method was used to solve the motion equations of the Flügge shell. Based on the continuity boundary conditions of displacement and stress, a semi-analytical model for calculating the dynamic response of a tunnel buried in an unsaturated full-space was proposed. The dynamic response of the soil-tunnel system and the effect of saturation on the dynamic response were analyzed. The results show that the soil saturation has a great effect on the magnitude of soil displacement, soil stress, excess pore water pressure and critical velocity. Therefore, it is necessary to take the effect of saturation into account when calculating the dynamic response.