Singapore’s Cross Island Line has reached a major construction milestone after workers completed the first breakthrough of a large-diameter tunnel between the future Tampines North and Defu MRT stations, marking a significant step toward the country’s next major rail expansion.
The breakthrough took place on Sept. 11 and represents the first of four planned tunnel breakthroughs involving large-diameter tunnel boring machines on the Cross Island Line. The completed excavation is part of the tunnel connecting the areas around Tampines North and Defu.
What makes the project particularly notable is the size and design of the tunnel. Instead of constructing two conventional tunnels, one for each direction, engineers are using a tunnel boring machine measuring about 12.6 metres in diameter to create a single tunnel capable of accommodating both MRT tracks.
The approach is designed to reduce the amount of underground corridor needed, potentially freeing up more space for future developments above ground. It also reduces the number of cross-passages normally required between separate tunnels for emergency access.
But building a tunnel of this scale underground presents its own engineering challenges. The larger machine produces substantially more excavated material, requiring higher-capacity systems for removing, handling and transporting the soil.
Engineers also equipped the tunnel boring machine with an accessible cutterhead that allows cutting tools to be replaced under normal atmospheric conditions instead of relying on compressed-air environments. Real-time cutter-wear monitoring and enhanced soil-conditioning systems were also incorporated to support safer and more efficient tunnelling.
The tunnel stretches roughly 2.9 kilometres between the two future stations and reaches deep underground. Earlier LTA information said the tunnel was designed to run about 35 metres below ground on average, with the deepest portions reaching around 50 metres.
The latest breakthrough, however, does not mean the tunnel is ready for trains.
Workers still have to complete substantial work inside the structure, including installing a centre wall separating the eastbound and westbound tracks. LTA plans to use precast wall panels and a specially designed erection gantry equipped with a robotic arm to position and install them. The method is intended to reduce manpower requirements and labour-intensive work inside the tunnel while improving construction safety.
The Tampines North-Defu stretch is part of the 29-kilometre Cross Island Line Phase 1, which will have 12 stations running from Aviation Park to Bright Hill. The line will serve eastern, north-eastern and central parts of Singapore and provide connections with existing MRT networks at Pasir Ris, Hougang, Ang Mo Kio and Bright Hill.
The Cross Island Line is planned to become Singapore’s eighth MRT line and, when fully developed, its longest fully underground rail line. The network is intended to connect major growth areas including Changi, Punggol Digital District and Jurong Lake District. LTA expects the entire line to eventually serve more than 600,000 passengers a day in its initial years, with ridership potentially exceeding one million over time.
Phase 1 construction is targeted for completion by 2030, with the Cross Island Line expected to begin opening progressively from 2030.
For commuters, the project could eventually mean more direct journeys and additional alternatives when existing MRT routes become crowded. For Singapore’s infrastructure planners, however, the bigger challenge remains completing one of the country’s most technically demanding underground rail projects while working around existing roads, infrastructure and densely developed areas.
The first breakthrough is now complete. The bigger question is how quickly the remaining tunnelling, station construction and railway systems can come together before the Cross Island Line finally begins carrying passengers in the next decade.
