Effects of tunnel shapes in structural and hydraulic interaction

Determining tunnel shapes requires the consideration of various factors such as ground and groundwater conditions, usage, economic efficiency, and constructability. In the case of particularly high water pressure environments, a circular tunnel is generally adopted to avoid the generation of stress concentration in the lining. However, because the circular cross section is difficult to construct and is not space efficient, a horseshoe- or egg-shaped cross section is usually employed. The effect of pore water pressure on tunnel linings has not been clearly identified yet. Furthermore, there are no established design guidelines for determining water pressure acting on the lining. In this study, the water pressure development mechanism and the effect of tunnel cross section is investigated using a coupled numerical analysis. It is found that the mode of water pressure and its effect on the lining are strongly dependent on tunnel shapes and hydraulic boundary conditions. Based on the analysis results a method for evaluating pore water pressure on the lining is proposed.