Feasibility studies on various SFT in Japan and their technological evaluation

Abstract Submerged floating tunnel (SFT) has been thought as a promising crossing technology and been studied in many countries for its realization. SFT has superior advantages to conventional crossing technologies such as bridge or subsea tunnel but it also requires technological innovation to keep the structural stability against environmental disturbance with safety measures for unexpected emergency. Therefore, various designs of SFT have been proposed for numerous crossing sites and its design standard has not yet been established. In Japan, the society of SFT research in Hokkaido, a consortium of the government, industries and academic organizations, had carried out a variety of feasibility studies through numerical simulations and experiments during the past 20 years in order to evaluate their applicability and to find out appropriate structural design. Geographical combination of water depth and crossing distance is one of the most important factors to decide the structural design as well as environmental conditions such as wave, current and earthquake. On the other hand, the balance of weight and buoyancy of the structure plays an important role to control the dynamic behavior of SFT when tension leg is used to stabilize a structure under water. Then, the materials used for the structure and the tension leg arrangements should be decided in order to satisfy those requirements. In this paper, recommended structural designs as well as their technological evaluation are introduced as a result of those various feasibility studies under different design conditions.