A preliminary study on design optimisation of submerged floating tunnels

This paper systematically studies the submerged floating tunnel, a concept initially proposed in the 19th century, only sporadically built, but possibly more viable potential in the future. The first part of this paper presents a literature review on submerged floating tunnel concepts with different design variables, where various type, plane alignment, cross-sections, tethers, and anchoring systems are discussed. Critical parameters for potential design are discussed, including submergence depth, Buoyancy-Weight-Ratio, and cross-section dimensions. The second part introduces an optimisation model of the complex engineering system of submerged floating tunnel, with a balanced approach to address appropriate type selection, weight balance consideration, structural deflection, tether capacity and slack prevention, and uplift/sliding stability of gravity type foundation taken. With given environmental parameters of water depth, crossing length, and wave/current characteristics, the optimal solution with minimum cost is obtained, with design variables including the tunnel's outer and inner diameters, tether's diameter and layout, and anchor mass optimised.