In Korea, a four-lane motorway is being constructed between the city of Busan and Geoje island, reduc- ing travelling times from one hour by ferry to just 10 minutes by car. The so-called Busan-Geoje Fixed Link consists of two cable-stayed girder bridges and a tunnel, crossing the bay of Jinhae. MARIN contributed to this unique infrastructure project with scale model tests and computer simulations.
The tunnel is being built by transporting each of its 18 elements below two pontoons from the construction dock to their final positions and lowering them on to the sea bed. The Busan-Geoje Fixed Link project is unique because the tunnel elements are installed in Jinhae Bay which has direct access to open sea. Therefore, a detailed assessment of the effects of incoming swells and wind seas was required.
Scale model tests in irregular waves were carried out in MARIN’s Shallow Water Basin. A detailed test set-up was constructed, includ- ing the trench in which the tunnel elements are placed. Models of a tunnel element, two pontoons, the mooring system, contraction lines and suspension wires were constructed at a scale of 1:50. Behaviour of the system was investigated under a range of different wave conditions. The motions of the pontoons and the submerged tunnel element were measured, as well as the tensions in the lines. Tests were carried out with the tunnel ele- ment suspended just 0.5 m above the gravel bed and at 1 m below the water’ surface.
After the model tests, a simulation model of the pontoons with the suspended tunnel element was constructed in MARIN’s time- domain simulation tool aNySIM. The large number of mooring lines, contraction lines and suspension wires resulted in a relatively complex model. A sensitivity study was also carried out, investigating the parameters most critical to the operation and the mooring system of the pontoons was further optimised.
To evaluate the operational limits of the tunnel immersion more than 6,500 time- domain simulations were finally carried out. The simulation results included motions, velocities and accelerations, as well as line tensions. The extreme values were used to perform a combined evaluation of more than 10 structural and operational criteria.
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