Singapore has officially completed the Circle Line loop with the opening of three new stations: Keppel, Cantonment and Prince Edward Road. Marking the culmination of a nearly 30-year journey, the completed loop enhances mobility and connectivity, offering faster, more direct connections between communities and key social, cultural and economic destinations.
AECOM was appointed as professional consultant to deliver the overall architectural and engineering design for the civil infrastructure of Circle Line 6 (CCL6), which encompasses the three new stations as well as nearly four kilometers of the tunnel alignment.
Engineering a route through a complex urban environment
One of the project’s most significant engineering challenges was the construction of bored tunnel between Keppel Station and Cantonment Station. With Keppel Station located near the junction of Keppel Viaduct and West Coast Highway, the tunnel had to pass through the pile foundations of two viaduct piers.
Fixed station locations constrained alignment flexibility, while challenging ground conditions heightened the risk of settlement and ground movement. Adding to the complexity, the Keppel Viaduct, a critical transport link, had to remain safe and fully operational throughout construction.
Tunneling under Keppel Viaduct
To overcome this challenge, our team assessed multiple tunnel alignment options through detailed geotechnical investigations, numerical modeling and Finite Element Modeling (FEM).
After several evaluations, load transfer of the bridge structures with underpinning works were identified as the most effective solution. New micropiles were installed alongside the planned tunnel alignment to create an alternative foundation for the viaduct. Using hydraulic jacks, the viaduct’s load was carefully and progressively transferred from its original piles to the new micropiles, with millimeter-level precision guided by rigorous engineering calculations and continuous real-time monitoring.
This innovative approach created the space needed for the tunnel boring machine (TBM) to pass safely beneath the viaduct and construct the tunnel. The result was a tunnel that met stringent safety, operational and passenger comfort requirements, while ensuring the Keppel Viaduct and surrounding transport corridors remained fully operational throughout construction, with no disruption to traffic.
Preserving history while building for the future
Protecting the historic Tanjong Pagar Railway Station was a critical priority during the construction of CCL6. Opened in 1932 and gazetted as a National Monument in 2011, the 94-year-old station sits directly above the tunnel alignment, with the TBM required to pass approximately 7 meters beneath its pile foundations.
To safeguard the structure, AECOM carried out detailed assessments of potential vibration and ground movement impacts. Preventive measures included deepening of the tunnel alignment, installing vibration monitoring points and deploying real-time displacement sensors in sensitive areas. During tunneling, the TBM’s advance rate and cutterhead torque were carefully controlled to keep vibrations within safe limits and protect the integrity of the monument.
AECOM was the Qualified Person for Design (QPD) for the preservation and reinstatement of the station’s historic platform canopy. To facilitate construction, the canopy was carefully dismantled in 2017, with comprehensive structural assessment and mapping. Following the completion of the major works, the canopy was meticulously reinstated in 2024, ensuring this important piece of Singapore’s railway heritage was preserved for future generations.
Innovative tunnel design in a constrained urban environment
At Prince Edward Road Station, severe space constraints and the presence of existing buildings above meant the tunnels could not be constructed using the conventional side-by-side arrangement. Instead, the tunnels were stacked vertically, an innovative design that minimized the project’s footprint below ground.
A protective underground canopy comprising large steel pipes were installed next to the stacked bored tunnel alignment, to facilitate the subway construction below Shenton Way. This created a safe working environment while protecting the live traffic and structures above.
The solution eliminated the need for major utility diversions, avoided road closures and traffic disruptions, and allowed nearby buildings to remain operational throughout construction in this densely developed urban area.
Designed for a greener transport network
Sustainability was a key consideration throughout the design and delivery of CCL6. The project is targeting BCA Green Mark Platinum certification under the Green Mark for Transit Stations scheme and features the Land Transport Authority’s first centralized cooling system. Located at Cantonment Station, the system serves all three stations along the CCL6 alignment, improving operational efficiency while reducing overall energy consumption.
To further lower the project’s environmental footprint, renewable energy is generated through rooftop solar photovoltaic panels and supplemented by energy recovered from train regenerative braking systems.
Beyond environmental performance, each station has been thoughtfully designed to reflect the character and heritage of its surrounding community:
- Keppel Station features architectural elements inspired by the iconic cable cars of the HarbourFront area, creating a strong visual connection to the locality.
- Cantonment Station, located beneath the former Tanjong Pagar Railway Station, incorporates design cues from the conserved national monument. A distinctive curved ceiling and large-scale artwork celebrate the site’s rich railway heritage. Its close proximity to several Housing & Development Board blocks at Everton Park and Cantonment Close seamlessly integrates the new transport hub into the residential community.
- Prince Edward Road Station draws inspiration from Singapore’s maritime history, reflecting the area’s longstanding connection to the waterfront and the nation’s seafaring legacy.
Closing the loop
Spanning 39 kilometers and 33 stations, with 12 interchanges connecting to Singapore’s MRT network, the completed Circle Line strengthens the efficiency and resilience of the nation’s transportation system. Commuters can enjoy more direct and flexible travel options, with reduced travel times and alternative routes to help ease congestion at major interchanges such as City Hall and Raffles Place.
For more than a decade, AECOM Singapore worked closely with Land Transport Authority to support this transformative project, providing design and engineering expertise, integrating sustainability consulting for greener outcomes, and delivering construction supervision services that contribute to a more connected and sustainable nation.