Submerged floating tunnel (SFT) is a new type of transportation infrastructure for crossing sea straits of relatively deeper water. Comparing with the fixed tunnel, the main challenge in designing a SFT is the stability maintaining in complex hydrodynamic environment, especially for the wave-induced dynamic load. In this study, a series of 2D experiments were conducted to investigate the hydrodynamic responses of the SFT under regular waves. The influence of several governing parameters is thoroughly analyzed, including the wave height and period, submergence depth, buoyancy to weight ratio (BWR), and the mooring line angle. The results show that the motion amplitudes of SFT increase with wave height increasing. The effect of wave period is related to the natural period of the structure. The sway, heave and roll of the SFT submerged beneath the water surface are much smaller than that of SFT on the water surface. With the increase of BWR, the motion of SFT decreases. The motion amplitude increases with mooring line angle increasing.


The submerged floating tunnel (SFT) is a concept going back at least 150 years and probably even further back. Historic records show that a rather complete understanding of this idea was brought forward by Sir James Reed, UK in 1886 and later in 1924 by Trygve Olsen Dale, Norway. Due to its complexity, practical SFT project has not yet been built all over the world. However, as a new type of transportation facilities, the SFT has so many advantages in terms of construction, economics and ecology for long span or deep water fiord conditions.

SFT is considered as one of alternatives for crossing sea straits of relatively deeper water. Compared to available strait-crossing techniques, namely bridges, immersed or undersea tunnels, the SFT offers many advantages such as lower environmental impact, less sensitivity to wind and seismic actions, higher adaptability to site morphology (Mandara et al., 2016). Moreover, SFT turns to be economically more affordable when long distances are to be covered (Martire et al., 2010), and even in those cases where a long suspension bridge is not feasible and undersea tunnels have to cope with hard geotechnical problems.

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