From tunnelling 1.8m under a live MRT line to diverting a canal: LTA sets out TEL3 engineering challenges

A section of an existing canal had to be diverted for the construction of Shenton Way MRT station along stage 3 of the Thomson-East Coast Line. PHOTO: LTA

SINGAPORE - During the construction of Outram Park MRT station along the Thomson-East Coast Line (TEL), engineers had to bore tunnels as close as 1.8m under the East-West Line (EWL).

Called “undercrossing”, the manoeuvre was performed for the first time by the Land Transport Authority (LTA), on a 365m stretch of TEL tunnels between Outram Park MRT station and Havelock MRT station. The distances between the TEL and EWL tunnels along that stretch range from 1.8m to 8m.

Meanwhile, train services on the EWL continued without a hitch, as LTA engineers monitored the “live” tunnels in real-time during tunnelling works to ensure safety.

Before works began, a pre-condition survey was carried out to test the EWL tunnels’ structure and integrity, said Ms Laurencia Syanti Wibawa, LTA’s deputy project manager for TEL Stage 3.

Running from Stevens, through Orchard and Outram Park to Gardens by the Bay, Stage 3 of TEL comprises 13 stations, 11 of which are opening on Nov 13.

Speaking to reporters last Friday, LTA engineers said the construction of each TEL station presented engineers with unique challenges.

For instance, land constraints forced them to use stacked stations in places like Napier. This is where two platforms – one above the other – are needed for a station, instead of the traditional bi-directional platform.

While building Great World MRT station’s Kim Seng underpass, contractors encountered multiple steel beams and plates underground, which did not show up on any historical records or ground surveys.

As a result, they had to shift from using only a micro tunnel boring machine underground to adopting a hybrid method – the machine was deployed where possible alongside a “cut-and-cover” method, which excavates a large trench that is then covered by a concrete deck so work can continue below.

This meant some work had to take place above ground, delaying the opening of three entrances. The station’s Entrance Two will open only at the end of 2022, while Entrance Five will open in the first quarter of 2023 and Entrance Three by the end of 2023 or in early 2024.

“The cut-and-cover method required more time to put in place the necessary traffic diversions for the adjacent condominiums and supporting structures for existing multiple utility pipes,” TEL project manager Lee Kar Guan said.

At Shenton Way station, which is surrounded by glass buildings such as Asia Square Tower 2, workers had to be extra careful, as Tower 2 is just 2m away from a wall of the station.

An aerial view of Asia Square Tower 2 before a temporary canal was built. PHOTO: SCREENGRAB FROM GOOGLE MAPS

LTA said tractors were installed with sensors to alert workers whenever they got too close to Asia Square Tower 2’s facade, while the load of the tractors had to be restricted to prevent ground vibrations from shattering the glass.

Engineers also had to divert a section of an existing canal measuring 299m long and 8m wide that lay above the Shenton Way MRT station. To do this, a temporary canal with a reinforced concrete base had to be constructed, using steel sheet piles and I-beams as walls.

Diversion works were implemented in phases using temporary dams.

Beyond overcoming engineering challenges, LTA said it had to placate residents, businesses and other people inconvenienced by the construction works.

For instance, contractors had to demolish a temporary pedestrian overhead bridge across Outram Road for a road realignment. Many elderly and wheelchair-using patients had used the bridge to get from the EWL station exit to a Singapore General Hospital (SGH) shuttle bus stop across the road.

For three months after the bridge’s demolition, LTA deployed ushers to help push wheelchair-users and guide the elderly to take a separate, slightly longer route to get to the shuttle bus stop. Later, it moved the SGH shuttle bus stop closer to a new MRT station entrance that opened in May 2021.

LTA engineers said the construction of each TEL MRT station presented engineers with unique challenges.  PHOTO: LTA

When the TEL Outram Park MRT station opens in November, the public can use a permanent, free-to-access 24-hour underpass to cross Outram Road as well.

At Havelock station, the LTA agreed to open a sheltered staircase at Entrance Three early in January 2022, after consultations between LTA, residents and Jalan Besar GRC MP Josephine Teo, who is also Minister for Communications and Information.

The sheltered staircase gave residents of Block 94 and 95 Havelock Road a more direct way to go between their blocks and the main road – previously they had to use an unsheltered ramp along a route that was much more circuitous.

LTA said building TEL Stage 3 was challenging due to the nature of the built environment around stations located in the city centre.

“It involved meticulous planning and the use of innovative engineering solutions to overcome these challenges.”

The 11 stations opening are Stevens, Napier, Orchard Boulevard, Orchard, Great World, Havelock, Outram Park, Maxwell, Shenton Way, Marina Bay and Gardens by the Bay.

The entire TEL will be fully open by 2025.

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