DEVELOPMENT OF DESIGN PROCEDURES FOR SUBMERGED FLOATING TUNNELS

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A submerged floating tunnel (SFT) is a kind of submersible structures moored by tension legs anchored in the sea bed and tensioned by buoyancy of the tunnel. Although SFT has not been constructed, it is expected as one of the most attractive technology for crossing straits. The purpose of this study is to investigate the design procedures for SFT.The important results obtained in this study are summarized as follows ;1) Hydrodynamic force acting on SFT can be evaluated by potential theory as well as by a modified Morison's equation expanded to apply to such problems. The values of the added mass coefficient and the damping coefficient in the modified Morison's equation have been proposed for the design of SFT.2) Analytical Models for 3-and 2-dimensional dynamic analyzes of SFT subjected to wave and seismic action have been proposed.3) In the design of SFT selection of tension leg type and apparent specific gravity is important to prevent slack of tension legs which may cause impact force called snap.4) Wave and seismic action are predominant loads in the design of SFT constructed in the coastal zone of Japan.5) Mechanical and structural characteristics of SFTs with vertical legs, oblique legs and combined vertical and oblique legs are analyzed.6) Fatigue of tension legs due to wave may be critical in the design of SFT.A practical method for checking safety for fatigue of tension legs has been proposed.7) Rigidity of the joint between tunnel elements has large effects on the dynamic properties of SFT.