CCL Tunnels: Reinforcement Works Address ‘Tunnel Squatting’ & Disruptions

Singapore’s Circle Line is undergoing extensive tunnel reinforcement work, a project expected to conclude by April 19, 2026, disrupting service between Mountbatten, Dakota, and Paya Lebar stations. The disruption, which began on January 17, 2026, is necessary to address a phenomenon known as “tunnel squatting,” a gradual compression of the ground surrounding the tunnels, and represents a proactive investment in the long-term reliability of the city-state’s mass transit system.

The Land Transport Authority (LTA) has completed the installation of steel plates on all 152 tunnel rings in the inbound tunnel towards HarbourFront station, but finishing work – including welding, grouting, and bolting – alongside rigorous testing procedures, are still underway. By project completion, more than 300 tunnel rings across both tunnels will have been reinforced. The work focuses on sections of the Circle Line built through soft marine clay, a geological condition common in Singapore that makes the tunnels susceptible to this type of deformation over time.

Tunnel squatting, if left unaddressed, poses a risk to both operational efficiency and structural integrity. The LTA has been monitoring the situation for over a decade, and the current reinforcement project is designed to prevent potential long-term disruptions and structural defects. The proactive approach underscores the importance of preventative maintenance in maintaining critical infrastructure, even at the cost of temporary inconvenience for commuters.

The project isn’t simply a matter of bolting steel plates into place. The LTA is deploying a specialized robotic arm to secure the plates within the tunnel. This automation significantly reduces the manpower required – from five to six workers per plate to a single robotic operation – and accelerates the process. This deployment highlights a broader trend within infrastructure projects: the increasing adoption of robotics and automation to improve efficiency, reduce costs, and enhance worker safety.

The service adjustments during this period are substantial. Trains are operating on a single platform between Mountbatten, Dakota, and Paya Lebar stations, leading to longer intervals on the entire Circle Line. Specifically, wait times have increased to three minutes during peak hours and five minutes during off-peak hours, compared to the previous two-minute intervals during peak times. Shuttle train services are running between Paya Lebar and Mountbatten stations at 10-minute intervals, and longer intervals are also in effect on sections of the line connecting to Dhoby Ghaut and Marina Bay. Approximately 480,000 passengers are affected daily.

To mitigate the impact on commuters, the LTA is providing shuttle bus services during weekday peak hours, excluding public holidays. Shuttle 38 will operate between Paya Lebar and Stadium, while Shuttle 37A will run from Serangoon to Paya Lebar, and Shuttle 37B and 37C will provide express services from Tai Seng to Bishan and Serangoon, respectively. These alternative transport options aim to alleviate congestion and provide commuters with viable alternatives during the disruption.

The financial implications of this project extend beyond the direct costs of materials and labor. While the LTA has not publicly disclosed the total project cost, the investment reflects a commitment to long-term infrastructure resilience. Preventing more severe structural issues and prolonged service disruptions in the future represents a significant cost avoidance strategy. The use of robotics, while requiring an initial investment, also contributes to long-term cost savings through increased efficiency and reduced labor requirements.

The Circle Line’s tunnel squatting issue isn’t unique. Similar geological challenges are faced in other urban rail systems built in areas with soft marine clay. The LTA’s proactive response and the implementation of innovative solutions, such as robotic installation, could serve as a model for other cities grappling with similar infrastructure challenges. The successful completion of this project will not only ensure the continued reliability of the Circle Line but also demonstrate Singapore’s commitment to maintaining a world-class public transportation system.

The current disruption underscores the ongoing need for investment in infrastructure maintenance and upgrades. While preventative measures like these may cause temporary inconvenience, they are essential for ensuring the long-term safety, reliability, and efficiency of critical transportation networks. The LTA’s approach highlights the importance of balancing immediate operational needs with the long-term sustainability of infrastructure assets.