Officials expect the tunnelling work to be completed in nearly a year and a half.

| Photo Credit: M. SRINATH

Building underground networks for the upcoming Chennai Metro Rail’s phase II project is gradually expanding to more areas in the southern parts of the city now. A few months after one section of underground network was completed from Light House to Thirumayilai, the next one from Thirumayilai towards Boat Club is all set to commence in the first week of August.Previously, the tunnelling at the 2.2-km stretch from Thirumayilai to Boat Club was scheduled to begin in June.Three metro corridors—Madhavaram to SIPCOT (corridor 3), Poonamallee to Light House (corridor 4), and Madhavaram to Sholinganallur (corridor 5)—form the 118.9-km phase II project.This 2.2-km underground stretch comes under corridor 4.Two tunnel boring machines (TBM) are being lowered and assembled at Thirumayilai station. Once launched, both these machines will pass through two stations—Alwarpet and Bharathidasan Road—and will be taken out at Boat Club station. First, the TBM in the down line will start the drilling process and it will be followed in the upline.“This is because from Thirumayilai till Bharathidasan Road, the tunnels are planned in a stacked pattern. It means, one tunnel will be above the other. In other locations, the tunnels are built next to each other (side by side). Tunnels are built in a stacked pattern for various reasons including if there isn’t adequate underground space,” a source said.According to officials of Chennai Metro Rail Limited (CMRL), they are expecting to bore through some hard rock and also clayey soil from Thirumayilai to Bharathidasan Road which could slow down the tunnelling work during the initial stage. “Drilling into hard rock continuously could demand frequent changing of the cutter discs of TBM (the tool which helps in excavation). But after Bharathidasan Road, the machines may mostly encounter only clayey soil and the machines can easily drill through and complete the process,” an official said.It could take nearly a year and half to complete the tunnelling from Thirumayilai to Boat Club. Published - July 02, 2026 05:11 am IST