Influence of soil-structure interaction on wave-induced responses of a submerged floating tunnel: The role of soil torsional resistance

초록

This study investigates the dynamic response of a Submerged Floating Tunnel (SFT) by incorporating soilstructure interaction, with a particular emphasis on the influence of torsional soil resistance. While conventional guidelines often neglect torsional resistance for buried pipelines, its role in the global behavior of longspan SFTs remains largely unexplored. A series of time-domain dynamic analyses were conducted using a Morison-equation-based finite element framework, where soil resistance was modeled using discretized nonlinear springs. The results demonstrate that neglecting torsional resistance leads to a significant overestimation of horizontal deflections and torsional rotations, failing to converge to idealized fixed-end behavior even at an embedment length of 300 m. In contrast, the inclusion of the torsional spring model allows for faster convergence to fixed-end-like responses and effectively alleviates internal bending and torsional moments. Furthermore, torsional resistance significantly increases the natural frequencies of coupled horizontal-torsional modes, shifting them away from the dominant wave energy frequency. Sensitivity analyses indicate that torsional stiffness has a limited influence on global motions, whereas torsional capacity governs the critical embedment length at which the response begins to increase rapidly. Based on these findings, a dimensionless stability index (Pi stability) and a serviceability-based criterion for critical embedment length are proposed.

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