SINGAPORE - Passengers using the Circle Line (CCL) will face delays of up to 30 minutes from June 11 to July 20, because of maintenance works that will be carried out on a stretch of the tunnel built on reclaimed land that “has been subject to greater pressure”.

Announcing this on Wednesday, the Land Transport Authority (LTA) said the works will affect services at seven stations – Dhoby Ghaut, Bras Basah, Esplanade, Promenade, Nicoll Highway, Marina Bay and Bayfront.

Trains will operate from only one platform from 9pm on most days during the six-week period, with two shuttle train services plying the affected stations.

LTA said routine inspections had found that a stretch of the CCL tunnel between Promenade and Nicoll Highway stations “has been subject to greater pressure”.

“LTA has assessed that this poses no safety risks to CCL train operations,” the authority said, adding that it will carry out precautionary maintenance and strengthening works, including installing steel supports to the tunnel rings “to ensure the long-term integrity of the tunnel”.

Responding to queries, an LTA spokesman said instruments set up to monitor this stretch of the CCL tunnel round the clock had picked up “localised incidence of higher-than-projected ground pressure”.

“Residual ground movement is common, and some settlement is still expected for some time after construction. This is why we monitor tunnel stretches located in reclaimed land consisting of marine clay, such as this CCL tunnel stretch, especially closely,” he said.

“At present, we have not detected a similar issue in other areas.”

The LTA spokesman also said all the tunnels are made with reinforced concrete segments, and their design took into account ground conditions.

The steel plates that will be added to the tunnel rings are an additional strengthening measure, he added.

To allow these works to be carried out, trains will ply the seven stations as shuttle services back and forth from 9pm till the end of operating hours for much of the period from June 11 to July 20.

Trains will run normally on June 16 to 18, 24, 28 and 29; and on July 1, 2, 7, 8, and 14 to 16.

There will be two shuttle services – one between Dhoby Ghaut and Promenade stations that will run at 15-minute intervals, and another between Marina Bay and Stadium stations, where trains will arrive every 20 minutes.

“This will result in longer headways, and commuters will experience additional travel times of up to 30 minutes,” LTA said.

The LTA spokesman said it had considered other approaches, including opening the line late or carrying out works only during normal engineering hours after service ends, over a longer period.

The partial closure “strikes the best balance between minimising disruption to passengers and completing the works within a reasonable period of time”, he said.

Prior to this, there were early closures along the North-South and East-West MRT lines to give maintenance teams more time to carry out renewal works several years ago.

And from May to September 2022, SBS Transit closed train services on one platform of the Sengkang-Punggol LRT line on weekends for maintenance works.

LTA advised commuters to plan their journeys ahead of time and use other rail lines or buses to minimise the inconvenience from the CCL delays.

They can refer to LTA’s MyTransport.SG mobile app and social media platforms, as well as those of CCL operator SMRT, for more details, it added.

Posters and station announcements will be rolled out at all CCL MRT stations and selected stations on MRT lines that interchange with CCL stations, LTA said.

Station staff will also be deployed at the seven stations to help.

Experts said that ground settlement and movement can be influenced by many factors, including the type of soil and even activities that may be happening some distance away but still cause disturbances, like piling and excavation works. They said constant monitoring is the only accurate way for engineers to know the actual conditions and take any necessary steps to pre-emptively address issues.

Mr David Ng, honorary secretary of the Institution of Engineers, Singapore, said it is likely that the rate of ground settlement at the identified area has been higher than the predictions considered in design. The announced measures to strengthen the tunnels will help maintain the “required factor of safety” that would have been designed into the tunnels.

Some commuters said they would avoid using the shuttle services if they can.

Mr Harshitha Balaji, 20, a Singapore Management University student, usually takes the CCL from Bras Basah to Dhoby Ghaut, where he changes to the North East Line to get home from school.

He said that if his commute is affected by the partial closure, he would rather walk the distance of about 600m from the campus to Dhoby Ghaut than wait for the train shuttle service.

Mrs Miruna Ranjan, 37, a civil servant who lives in Queenstown and works at the National Stadium, does not usually leave her workplace after 9pm but said that if her commute were affected, she is likely to opt to take a ride-hailing service, rather than spend more time on the train to get home.

She said: “I think it will be students who rely solely on public transport to get around Singapore who would be most affected by the works.”

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* Additional reporting by Yugesh Kannan

This article was first published in The Straits Times. Permission required for reproduction.