Improved shield tunnel design methodology incorporating design robustness

This paper presents an improved design methodology for shield tunnels. Here, a new framework for three-dimensional analysis of shield tunnel "performance" (defined herein as the structural safety and serviceability of each tunnel ring) is developed, which considers the effect of the longitudinal variation of input parameters on the tunnel performance. Within this framework, random fields are used to simulate the longitudinal variation of input parameters, and the three-dimensional problem of shield tunnel performance is solved through a two-stage solution involving a one-dimensional model (for tunnel longitudinal behavior) and a two-dimensional model (for performance of segment rings). Furthermore, the robust design concept is integrated into the design of shield tunnels to guard against the longitudinal variation of tunnel performance caused by the longitudinal variation of input parameters. In the context of robust design, a new measure is developed for determining the robustness of the tunnel performance against the longitudinal variation of noise factors. A multi-objective optimization is then performed to optimize the design with respect to the design robustness and the cost efficiency, while satisfying the safety and serviceability requirements. Through an illustrative example, the effectiveness and significance of the improved shield tunnel design methodology is demonstrated.