In this paper, the behaviors of the ground-tunnel interface of submerged floating tunnels (SFTs) and traditional bored subsea tunnels are investigated through numerical analyses. The analyses consider both permanent loads (self-weight, hydrostatic pressure, buoyancy etc.) and environmental loads (currents, waves, tides etc.). In order to simulate accurate subsea conditions, the magnitude, influence factors, governing formula and characteristics of each load type are discussed and determined. The analyses show the maximum stress and maximum displacement distributions along the ground-tunnel interface. The results can be used to suggest a three-dimensional ground reinforcement scheme based on additional stiffness requirements and ground deformation ranges.
Ongoing globalization has increased the demands for maritime and aviation transportation of humans and natural resources. Transportation using conventional shipping vessels and aircraft is limited by environmental disasters and mostly focus on mass transit. In recent years, subsea tunnels have become a major alternative that can overcome the aforementioned weaknesses. With the advances in offshore geotechnical engineering and construction technologies, the concept of Submerged Floating Tunnel (SFT) which can create linear paths through the sea has become a potential solution. In order to utilize SFTs and maximize their advantages, it is vital to connect the tunnel path to existing or artificial islands. The connection to the ground is an economically viable option for necessary ventilation systems, emergency exits or rest stops, especially for long-span SFTs (Mazzolani, et al., 2010). When the SFTs are connected to the underground tunnel built in the island, two tunnels show different behaviors. The SFT moves dynamically due to the wave or traffic loads (Hongsheng et al., 2016). Unlike the SFT, the subsea bored tunnel inside the island shows less static displacement because the surrounding ground prevents the displacement of the tunnel. Since the two tunnels show different behaviors, the stability of the connection at the boundary between the ground and the ocean is very weak. Therefore, the connecting site has to be designed with additional consideration of the behavior characteristics in two environments. The design should be considered differently depending on the characteristics of the marine environment in which the SFT is located and the characteristics of the ground where the underground tunnel is located. So, it will be analyzed depending on the target site. Usual SFTs construction accompanies the design of anchors and tunnel segments. So, the design of the connecting site between the subsea bored tunnel and SFT has to be conducted with the consideration of the characteristics of the entire construction also.
