Busan-Geoje Fixed Link tunnel elements successfully positioned

After preparations that have taken more than five years, Daewoo Engineering & Construction has taken an important step towards completing the fifteen kilometre-long road link between Busan (the most important port in South Korea) and the island of Geoje. The first 180 meter-long tunnel elements, which form an important part of the Busan-Geoje Fixed Link, have been successfully sunk into place.

The Fixed Link consists of various sections: a 3.4 kilometre-long tunnel, submerged as deep as 50 metres below sea level, some cable bridges and fixed road links. TEC (a consortium formed by Royal Haskoning, DHV and W&B) staff have been giving technical advice on the design and construction of the tunnel for more than five years. In the opinion of Peter de Haas, a Royal Haskoning consultant, this has been “A technical tour de force in view of the difficult local conditions: a Pacific Ocean wave regime, a soft substrate and some of it above the sea floor. When the Busan Geoje Fixed Link is completely finished, it will be possible to drive from Busan to Geoje in 50 minutes.”

After Seoul, Busan is the second largest city in South Korea and is the country’s most important port. The city is highly industrialised and has a large container transhipment port. Because the city with its more than a million inhabitants is surrounded by high mountains and the ocean, there are hardly any options for expansion for housing, employment, industry and recreation. The population density is almost as great as that of the Randstad—the conurbation of the western Netherlands. Thanks to the direct connection with the islands of Geoje en Gaduk created by the Busan-Geoje Fixed Link, expansion can be realised there for both industry and recreation. The Geoje Fixed Link will provide a four-lane road link between Busan and the island of Gaduk and will also connect the uninhabited islands of Daejuk, Jungjuk and Jeo with each other.

Challenges
The TEC consortium has had to cope with many challenges,” explains Peter de Haas. “It’s not easy working in Korea. The language is a barrier because not many Koreans speak English. Our biggest challenges however were sinking the tunnel elements in the local wave regime and the depth of the sea floor. Sinking a tunnel into place under such extreme conditions had never been done before. The basic design for the tunnel that was finally approved was based on the Oresund tunnel between Denmark and Sweden. The Korean tunnel however has a very different topography such as, soft clay instead of rocky soil, a sea floor that is 50 metres deep instead of 20 metres and not much swell compared with the open waves of the ocean.”

Intensive research
Many alternatives for significantly improving the soft clay were investigated, calculated and designed. In the end, the technique normally used locally provided the best solution. Another challenge was predicting the wave regime for a long enough period to be able to sink the tunnel elements safely. In the end, the Danish Hydraulic Institute was able to provide a reliable system. “A lot of intensive research has been carried out by TEC for this Busan-Geoje Fixed Link,” according to Peter de Haas, “but until the first element was actually sunk into place we were on tenterhooks to see whether everything would go as predicted by our computer programs.” We believe that the knowledge Royal Haskoning has accumulated during this major project will provide new opportunities for designing other submerged tunnels.”

Contact: Peter de Haas
+51 14224941
p.dehaas@royalhaskoning.com

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