When the Thomson-East Coast Line (TEL) section of Orchard MRT station opens in 2021, commuters can enjoy a seamless transfer between the North-South Line (NSL) and TEL platforms, thanks to a passageway running beneath Orchard Boulevard.
The Land Transport Authority (LTA) revealed yesterday how this is being constructed without disrupting the heavy traffic along Orchard Boulevard or inconveniencing commuters using Orchard MRT station.
A method called pipe-roofing, previously used for the construction of a station on the Downtown Line, was employed. It involves creating an underground canopy of interlocked steel pipes, each with a diameter of 1.2m, around the tunnel.
This allows mining to be carried out without compromising the road or buildings above, according to Mr Henry Foo, the LTA's deputy group director for the TEL and the Cross Island Line.
Micro tunnel-boring machines were deployed to tunnel through the ground to install the pipes. These are about eight times smaller than the regular ones used for MRT tunnelling. The use of interlocking pipes also prevents misalignment and breakage of the pipes.
Prior to the construction of the canopy, work was done to stabilise the ground and prevent water from leaking into the tunnel. Steel frame supports were installed later on.
Mining within this set-up was completed last December and a permanent concrete tunnel is currently being built.
The mining and underpinning being done underneath Orchard MRT station to connect the two platforms are a "major engineering feat", said Mr Foo.
It is done using special drilling machines, which can drill in all directions within a confined space. The work has to be done incrementally so as not to disrupt train services.
Work will also be done to Orchard MRT station to add escalators, a lift and a staircase to link to the TEL platform.
The LTA said "detailed planning and close coordination" were being done with transport operator SMRT so as not to disrupt station operations or inconvenience commuters, adding that most of these works can be done only after service hours.
A separate pedestrian underpass is also being constructed to connect the TEL section of the interchange station to Ion Orchard and Wheelock Place malls.
Senior Minister of State for Transport Janil Puthucheary, who visited the worksite yesterday, said these works showed the innovation and smart engineering being employed in the construction of the TEL.
The expansion of Singapore's rail network is not without its problems, he added.
"As our network becomes denser and longer, the consideration of what we have to do next changes, because we don't want to interfere with what we have today (the existing MRT lines)," he said.
When completed, the 43km-long TEL will have 31 stations stretching from Woodlands North to Sungei Bedok.
It will open in stages from next year, beginning with three stations - Woodlands North, Woodlands and Woodlands South.
Correction note: In an earlier version of the story, we said that pipe-roofing is being used for the first time on an MRT project here. LTA has since clarified that it was previously used on the Downtown Line.