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Ground-freezing to be used for construction of Thomson MRT Line

Sections of the Thomson Line will need to built around existing train lines underground. In a first for rail construction in Singapore, special pipes will be used to freeze the ground to prevent water seepage.

SINGAPORE: From a quiet terminus of the North-South Line, Marina Bay MRT Station has since transformed when its Circle Line station opened in Jan 2012.

When the third phase of the Thomson Line opens in 2021, Marina Bay will become a major interchange serving three lines. However, construction at one section will pose a challenge, as it needs to cross the existing two MRT lines.

Thomson Line will be built below these lines, which means some foundation piles would need to be removed. First, a pedestrian linkway will be built beneath the tunnel. Once sufficient support has been added, about 20 piles in that 40-metre stretch will be removed. Freeze tubes will then be added - a first in the history of Singapore's rail construction.

"The key challenge is in constructing the pedestrian linkway and the tunnels, which run directly below the North-South and Circle Lines' existing tunnels, and coupled with the poor soil condition in the area makes the construction of the Marina Bay station very complex and very challenging, said the Land Transport Authority's Director of Civil Team 4 for the Thomson Line Shaik Sha Marican.

"To alleviate the problem of soil conditions, what we're going to do is ground-freezing, which technically is to freeze the ground to turn the ground water into ice, to form ice wall, so that to facilitate the construction to solidify the ground and to facilitate the construction of the tunnel." This will prevent water from seeping in and weakening the soil.

Construction will then start for the first tunnel, which will be used by the Woodlands-bound train. Finally, the tunnel for the Changi-bound train will be built in between. When completed, the tunnels will be 41 metres below ground surface.

Over at Orchard Road, the already bustling station will also be an interchange of the Thomson Line. The new station will be built on the green patch opposite ION Orchard. There will be two links - a platform linkway for commuters who need to change trains, and an underpass for other pedestrians. During construction, the glass canopy at ION Orchard will be dismantled.

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