Chennai Metro Rail Limited (CMRL) has invited bids for the construction of one of the toughest underground stretches on phase-2 from Kolathur to Nathamuni covering 5.8km. The 118.9km phase-2 is expected to be ready by 2025 and the 5.8km line from Kolathur to Nathamuni is the only underground stretch on corridor 5 from Madhavaram to Sholinganallur. It has now invited bids to construct the underground line with twin tunnels for the up and down line and link it with five underground stations at Kolathur junction, Srinivasa Nagar, Villivakkam suburban station, Villivakkam bus-terminus and Nathamuni. During the initial soil investigation, CMRL identified the line from Kolathur to Nathamuni as one of the two toughest stretches in phase-2 due to its soil type, which is primarily hard rock like black granite or a mix of quartz or charnockite. The rock soil condition could pose an engineering challenge as the tunnel boring machines will have to be operated at an appropriate speed — even as slow as below 8m a day — to control the vibrations while drilling to a minimum else it may affect nearby buildings. Tunnels on this stretch are going to be built at a depth of 15m to 21m. It may be recalled that in January 2021, only one firm bid for the construction of this stretch when CMRL floated a tender for the line for the first time when the bidder also quoted more than CMRL’s estimate, leading to its cancellation.
