Construction of an 8.2km motorway between Busan — Korea’s southernmost, second largest city — and the island of Geoje, called the Busan-Geoje Fixed Link Project, is currently underway. As part of this four-lane fixed link, there will be a submerged tunnel section of 3.2km in length. COWI and Daewoo Engineering Co. have formed a joint venture (CDJV) to carry out the design of the immersed tube tunnel (Busan-Geoje Fixed Link Immersed Tunnel). The Immersed Tunnel consists of 18 Tunnel Elements and will be constructed from East to West. The immersed tunnel will become one of the longest in the world to date, especially in an area of significant seismic activity. Each of the 18 elements is identical, although they will be placed in water depths varying from 15m up to 50m subjected to waves and current. The prefabricated tunnel section will be brought to the site in a submerged condition, where it will be suspended from immersion rigs by four wire ropes. Each tunnel section will be lowered and connected to the previously installed element. The immersion rig pontoons and the submerged tunnel element will be moored to stay in position using as many as 14 wire ropes. This paper describes the unique immersion concept specially developed for this project, the salient features of each phase of analysis and the major conclusions. The findings in this study are expected to aid designers of similar immersion process concepts to ensure safe installation.

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