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Chennai: Chennai Metro Rail Limited (CMRL) is set to create an engineering landmark with its upcoming Thirumayilai station, which will be the deepest underground metro station in the city at approximately 38.79 meters (over 127 feet) below street level. Forming a critical interchange in the ambitious Chennai metro Phase-II expansion, the station is expected to be operational by 2028, according to project officials.
The station’s complexity stems from its role as the intersection point for two major corridors: Corridor 3 (Madhavaram-SIPCOT) and Corridor 4 (Poonamallee-Lighthouse). To navigate the narrow surface roads above—Kutchery Road and Royapettah High Road—the design avoids land acquisition by stacking the lines vertically underground.
The four-level subterranean structure will include a large concourse and three platforms arranged in a unique vertical configuration:
Officials acknowledge significant construction challenges due to the station's depth and local geology. Geotechnical surveys have identified rocky soil, complicating the construction of the station box, diaphragm walls, and subsequent tunneling.
Despite these hurdles, work is progressing on the ₹63,246-crore Phase-II project, which is approximately 40% complete overall. Diaphragm wall construction is currently underway at multiple locations from Madhavaram to Taramani and is expected to conclude in the next 6–8 months. Following this, CMRL will commence major tunneling operations, utilizing 23 Tunnel Boring Machines (TBMs). The TBMs will arrive after design approvals and factory testing.
The Phase-II network will span 118.9 km with 128 stations across three new corridors. To date, about 19 km of the planned 50.5 km of tunnels have been completed.
The first operational section of Phase-II is on track for a December 2025 opening: the 9-km elevated stretch from Poonamallee to Porur. The Poonamallee station construction is in its final stages. Officials are also targeting the subsequent inauguration of the Porur-Kodambakkam route soon after.
In a recent milestone for Corridor 4, critical equipment, including a motor trolley and a road-cum-rail vehicle for overhead electrification works, was successfully transported from the Poonamallee depot to Mullai Thottam station. This marks the start of grade separator construction, a key step in building the elevated sections.
Once completed, the Thirumayilai interchange will not only be a feat of engineering but also a vital node, seamlessly connecting north, south, and western parts of Chennai, significantly boosting the city’s integrated transit network.
