TBM peacock
\| Photo Credit: Special Arrangement

In a couple of days, as you travel in Chennai Metro Rail trains through the tunnel of the phase I network at Nandanam, a mammoth tunnel boring machine (TBM) would be quietly crawling underneath, creating another tunnel in which commuters will travel in future.

In the 118.9-km phase II network, the corridor 4 from Poonamallee to Light House will criss-cross the phase I network’s tunnel at Nandanam. As a part of this corridor has been designed as an underground network from Kodambakkam to Light House, Chennai Metro Rail has been building tunnels in short sections.

So far, two tunnel stretches — Light House to Thirumayilai and Panagal Park to Kodambakkam — have been completed. In December last year, Chennai Metro Rail commenced tunnelling from Panagal Park yet again to bore towards Boat Club via Nandanam.

According to officials of Chennai Metro Rail Limited (CMRL), this TBM which departed from Panagal Park has now landed close to the phase I Nandanam Metro Rail station after boring through a distance of 868 metres. The machine bored through medium sand, clay and shale stone to reach Nandanam. A process called cutter head intervention (wherein the cutter head discs that helps in boring through are repaired or changed) was carried out eight times for the TBM during the course of the tunnelling from Panagal Park to Nandanam.

T. Archunan, director (projects), CMRL, said the Commissioner of Railway Safety (CRS) has given approval for the TBM to bore under the phase I Nandanam tunnel. “In a few days, the machine will bore perpendicularly under the phase I tunnel at a depth of 29.8 metres from the ground. We have placed sensors and have been monitoring the tunnel on a real time basis for the last two weeks to ensure the vibrations are within the permissible limits and there are no issues of settlements or cracks. So far, the vibrations are under control. So, we don’t need to impose speed restrictions, and the train operations will continue as well,” he said.

If the vibrations or settlements start to increase even by the slightest measure, then the speed of the trains which are entering the Nandanam station will be reduced for safety reasons, he added. The TBM is likely to bore under phase I tunnel at Nandanam junction for nearly two weeks. Officials said the TBM will drill through silty clay and medium sand and is likely to arrive at Boat Club in December this year.

Published - July 23, 2026 05:00 am IST