CHENNAI: Chennai Metro has dug its way to a new milestone, successfully tunnelling beneath an existing operational double tunnel metro line, without disrupting passenger services on the blue line connecting Airport and Wimco Nagar.
Two tunnel boring machines have passed directly beneath the live Nandanam metro tunnel — between Nandanam and Saidapet Metro stations — clearing a key engineering hurdle for the underground section of Corridor 4 of the phase II project.
Kodambakkam-Panagal Park underground stretch is expected to be completed around June 2027, T Archunan, director (projects) of CMRL, told TNIE. The new tunnels, each 5.8 metres wide, are being constructed more than 20 metres below ground, while the existing tunnels are around 10 metres below the surface.
The vertical separation allowed the TBMs to pass beneath the live line safely, Archunan said. “The engineering achievement builds on an earlier milestone in the Kilpauk section of Corridor 2, where a tunnel boring machine passed beneath the existing Kilpauk Metro station stretch tunnel under Corridor 2.
That operation involved crossing a single tunnel. The latest work involved two existing tunnels, raising the engineering complexity of the operation. The phase II tunnels were 6.85 m below the phase 1 tunnels,” said Archunan. The stretch is part of a wider 4.9 km underground corridor linking Boat Club, Nandanam, Panagal Park and Kodambakkam. The entire corridor is targeted for completion by December 2027, he said.
The Corridor-4 underground package includes four underground stations, twin bored tunnels, a crossover at Panagal Park, a cut-and-cover box, a U-section and an elevated ramp. The twin tunnels between Panagal Park and Kodambakkam, covering 1,154 metres, and those between Panagal Park and Nandanam, covering 868 metres, are ready.
The 750-metre stretch between the Nandanam ramp and Kodambakkam station and the 290-metre cut-and-cover box have also been completed. The remaining tunnelling work involves 263 metres of the planned 868-metre twin tunnel between Nandanam and Boat Club.
One of the two TBMs is now about 300 metres from Nandanam station on Anna Salai and is approaching its breakthrough point. It is expected to reach Boat Club station by December, with retrieval planned for January 2027, said Archunan.
The breakthrough will allow the remaining station and tunnel works in the section to proceed towards the December 2027 completion target. At Kodambakkam and Panagal Park, major structural works are expected to be completed by December this year. Nandanam and Boat Club stations, however, are only about halfway complete.
