Mergor, a subsidiary of Strukton, successfully immersed the deepest element of the immersion tunnel near the South-Korean city of Busan on 16 October 2009. The element was placed at a depth of 50 metres. The Geoje Fixed Link connects the second capital of South Korea, Busan, with the Geoje peninsula, reducing the travel time between the two from 2.5 hours to just 50 minutes. The tunnel is 3.2 kilometres long.
The tunnel element is number 13 in a set of 18 elements. Tugboats were used to transport the tunnel element from the mooring location near TongYuong to the immersion point between Jungjuk and Gaduk Island, near Busan, South Korea. The immersion of the tunnel elements is performed with the help of two large catamaran pontoons equipped with an anchoring and positioning system. This system is the only one of its kind in the world.
In order to work at this depth, Mergor uses an innovative survey system that was specially developed for this project. Traditionally, measurements were made with total stations on measurement towers. However, with large distances, that system has significant measurement inaccuracies. With the help of the survey system’s Tautwire and Distance probes, it is possible to position the tunnel to an accuracy of a few millimetres at all times.
The advanced wind and wave prediction system allows Mergor to predict the necessary weather window within five days. During the entire operation, engineers work hard to analyse the available data, making it possible to immerse a tunnel element within a very narrow weather window.
The diving escort and the underwater tests during the immersion operation are performed by Strukton subsidiary OTN (Onderwater Techniek Nederland), which has deployed submarine Aurora for this purpose. This ‘Self-Propelled Diving Bell’ is a completely modernised, well-equipped submarine with modern, on-board navigation systems. It can operate to a depth of 300 metres and is used for underwater inspections and other underwater activities. It can also operate as a diving bell.
The last element will be immersed in March or April 2010 and project owner Daewoo Engineering can then finish the tunnel.