SINGAPORE: Ground-freezing technology is being used for the first time by the Land Transport Authority (LTA) to stabilise the earth before tunnel excavation works are carried out in MRT projects, in a bid to minimise disruptions to train operations during construction.
The technique has been used to create ice walls as part of works to construct a stretch of tunnels at Thomson-East Coast Line’s (TEL) Marina Bay station, LTA announced on Monday (Jun 25).
LTA said the ice walls were used to stabilise the ground and ensure that construction works will not impact operations on the Circle Line and North-South Line tunnels located above the TEL tunnels.
"Over the years, LTA has tunnelled through many different kinds of ground conditions, but this is the first time that ground-freezing technology is used in an LTA construction project. The ground here consists of old alluvium clay which is hard to stabilise with cement grouting," said Mr Ng Kee Nam, group director for TEL and Cross Island Line (Civil).
"Before the start of tunnelling works, we carried out multiple site checks and soil investigation works to decide on the best system to stabilise the ground. Ground-freezing method was found to be most suitable,” he added.
According to LTA, the technology was adopted for Marina Bay Station by installing a series of freeze pipes into the ground.
"Chilled brine at a temperature of -30 degrees Celsius is circulated within the freeze pipes, to allow the surrounding soil to freeze and form individual ice columns,” LTA said.
“The columns will then grow in size and join together with neighbouring columns to form one continuous, impermeable ice wall,” it added.
LTA said the ground-freezing process at the TEL Marina Bay Station started in March this year. After about two months, two ice walls about 1.8m in diameter were formed about 40m below ground.
The ice walls will be in place for about three months until the construction of the TEL’s Woodlands-bound tunnel is completed, LTA said.
The freeze pipes will then be deactivated, allowing the ground to thaw before construction works for the Upper Changi-bound TEL tunnels above it commence.
The construction for the TEL Marina Bay Station and its tunnels are expected to be completed in 2021.
The 43km long TEL will add 31 new stations to the existing rail network, with seven interchange stations linking it to all five existing MRT lines.
It is targeted to be fully operational by 2024.