The tunnels connecting Mountbatten, Dakota and Paya Lebar stations will be closed one at a time for the works, which will address tunnel squatting.
The phenomenon is caused by the soft marine clay that some stretches of Circle Line tunnels are built in and, if not addressed, could lead to disruptions in train operations and structural defects in the tunnel in the long term.
The LTA has been monitoring the issue for the past decade. It has identified three localised sectors of the CCL tunnels between Stadium and Paya Lebar stations that are more affected by tunnel squatting.
The organisation says expert consultants have confirmed that train operations can continue safely in the affected tunnels while LTA closes each tunnel in turn at the three localised sections – a total of 450m.
During the strengthening work, steel plates will be installed along the circumference of the affected tunnel segments.
The LTA says it has studied best practices in Shanghai, Taipei, Busan, Barcelona and Lisbon where similar engineering challenges were encountered. In some of these countries, full-scale tunnel segments loading tests have also been conducted to establish the conditions for tunnel safety to be maintained against long-term tunnel squatting, and similar measures have been carried out to address the issue.
