Busan-Geoje Fixed Link

The immersed tunnel is part of the Busan-Geoje Fixed Link: a unique project that was conceived in response to major economic and social issues in the region. The project, with a total investment value of EUR 1.5 billion, connects the second capital of South Korea with the Geoje Peninsula via two cable-stayed bridges with spans of 475 metres and 2 x 230 metres respectively and an immersed 3.2-km tunnel.

Client:
Daewoo Engineering & Construction
Location:
Busan
Number of elements:
18
Immersion:
2008
Specials:
50 metres deep
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Project

This was an exceptionally large assignment for Geocon: the contract amount for the immersion operation had been set at EUR 70 million. The principal for the immersion operation was Daewoo Engineering & Construction, a part of the project PPP consortium GK Fixed Link Corporation.

Tunnel segments

Over the course of three years, the Strukton and Geocon team immersed a total of 18 tunnel segments, each of which had a length of 180 metres. The deepest-lying segments were positioned some 50 metres below sea level – exceptionally deep for an immersed tunnel.

Due to the depth and length of the planned tunnel, utilising the more common survey mast and access shaft approach was not an option. The team responded by both developing new custom measurement systems for the project and implementing existing methods and solutions.

Measurement systems

Automated total stations

The primary measurement system used for the first four tunnel segments was based on self-tracking total stations. During the four immersion sessions, the team tested newly-adopted measurement systems like GPS, tautwire, distance sensors and the USBL system against the proven approach based on total stations.

The constant analysis of these new readings played a crucial role in optimising the newly-developed systems in this initial phase.

GPS

During the preparations for the immersion of the tunnel segments and the immersion operation itself, the team used a combination of position receivers and GPS compasses.

Tautwire

Geocon developed a custom tautwire system for this project that allowed for extremely accurate positioning during the immersion of the tunnel segments.

USBL

Using USBL in underwater positioning is hardly unique. What is unique however is using the system for positioning immersed tunnel segments! Like the tautwire, this system was used to direct the segment’s immersion until the guide pin had been inserted in the bracket.

Distance sensors

Connecting the new segment with the previously-immersed segment is one of the most exciting and critical stages in the entire immersion process. Accurate positioning is of paramount importance at this stage. The distance sensors developed especially for this project provide millimetre-accurate data about the precise position of the immersed tunnel segment.

Innovations

This project yielded a large number of innovations in the area of immersion measurement and visualisation including:

Busan-Geoje Fixed Link (part 1 of 2)

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Busan-Geoje Fixed Link (part 2 of 2)

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