In what is a first for construction in Singapore, ice walls are currently being used for building underground tunnels for the Thomson-East Line (TEL). This was announced by the Land Transport Authority (LTA) on Monday, June 25, at the tunnel toward Woodlands for the TEL at Marina Bay Station.
Two ice walls have been built measuring 1.8 meters in diameter. According to the LTA, this method, which freezes the ground, is necessary to make the earth sufficiently stable to handle tunnels being constructed 40 meters below ground level.
Mr. Ng Kee Nam, LTA group director for Thomson-East Coast and Cross Island Lines, said that this method is necessary due to the type of soil found in the Marina Bay area, which is likely to contribute to water seepage. The ice walls hold the water in, so that workers can do their underground jobs safely.
He said, “We have to maintain this wall for three months to allow the workers to complete the excavation. Throughout this period, we also have to maintain the temperature (of -30°C) to ensure the wall is always there.”
Construction of the ice wall started earlier this year, in March, when 96 freeze pipes were laid into the ground. A salt and water mixture (brine) with a temperature of -30°C was then passed through the pipes, freezing the soil and causing the formation of ice columns. These columns have been growing since March, and have now formed into ice walls.
Once work on the tunnel is finished, the freezes pipes will be shut off, and the ground will thaw.
Over the last two weeks, the ice walls have already allowed the workers to dig through a 6 meter portion of the tunnel. It is expected that these ice walls will be used for another three months, after which work will start on the TEL tunnel portion towards Changi Airport, at a more elevated area which will not need frozen walls for construction. Mr. Ng said that this part has soil consisting of marine clay, so traditional methods can be used again.
The TEL construction site was visited by Khaw Boon Wan, the Transport Minister, yesterday. According to the LTA, the building of the Woodlands North, Woodlands and Woodlands South Stations are on track for their scheduled openings in 2019.
The TEL is expected to be completely operational by 2024. However, it will open in phases starting in 2019. The Marina Bay Station is scheduled to be operational by 2021.