Laying giant concrete and steel modules beneath Hong Kong’s Victoria Harbor, one of the world’s busiest fairways, is quite an engineering challenge. With technology so much a part of our lives these days, one may think that boring a tunnel under a narrow waterway is as easy as hopscotching from one square to another. It is not.
The MTR Corp. has started tunneling – or more precisely, brick-laying – beneath the harbor for the HK$80 billion, 17-kilometer Shatin to Central Link that will add a fourth harbor-crossing tunnel to its rail network, after the tunnels of Tsuen Wan Line, Tung Chung Line/Airport Express and Tseung Kwan O Line.
The tunnel, slated to be up and running by 2021 to cut journey time between Hung Hom and Admiralty from 18 minutes to just five, is built by immersing and connecting 11 gigantic precast, reinforced concrete sections, cast in place and fabricated at the Shek O casting yard, along trenches dredged in the seabed across the harbor.
Before being towed one by one into the harbor, these parts will first be transshipped via a holding area near Tseung Kwan O for installation of two 30-meter surveying towers equipped with global positioning system to ensure correct horizontal and longitudinal movements.
Each up to 23,000 tons in weight and around 160 meters in length – like a 50-storey skyscraper being laid down – the first of the 11 giant units for the immersed tube tunnel was installed into the seabed in the vicinity of the Causeway Bay Typhoon Shelter this month.
An immersed tube is a kind of underwater tunnel composed of segments, constructed elsewhere and floated to the tunnel site, attached to floating pontoons equipped with mooring wires and other immersion equipment to be submerged into place and then linked together.
Starting from mid-June, water is to fill the ballast tanks, about 4,500 cubic meters each, fitted inside the tunnel unit for submersion some 20 meters beneath the sea surface in Causeway Bay into the excavated trench.
This phase is quite crucial: the installation of the first batch of units affects the precision of the entire tunnel and the margin for deviation is minimal.
A crew of 50 engineers and operators were deployed for continuous monitoring and tuning of the sinking position. The entire installation is expected to be finished in two years.
The tunnel will then link Hung Hom station with the new Exhibition station at the Wan Chai promenade, extending the century-old East Rail Line from Kowloon to Hong Kong Island for direct train rides all the way from Admiralty to Lo Wu/Lok Ma Chau stations without any interchange.
Having been involved in the construction of three immersed tube tunnels in Hong Kong since 1986, Fumihiro Aikawa, construction manager of MTR Corp., said he is proud to be a part of the project.
“I am privileged to be given such splendid opportunities to work in these challenging projects which form the most valuable memories in my career,” Aikawa said in an MTR press statement.
“I am now very excited to have the opportunity to build an immersed tunnel in Hong Kong again after 20 years and I am proud to work with the team to further enhance Hong Kong’s transport network.”
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Tunnel units are first cast and fabricated at a Shek O quarry and then towed, with the help of global positioning, into the Victoria Harbor for submersion. Photo: MTR