Chennai Metro Rail Limited (CMRL) invites bids for the second time in 2021 for the construction of one of the toughest underground stretches on phase-2 from Kolathur to Nathamuni covering 5.8km.
The stretch is considered challenging due to its rocky soil condition. The first tender floated for the stretch in January 2021 was one among six construction tenders cancelled as they either did not find many takers or quoted more than the actual estimate. The 118.9km phase-2 is expected to be ready by 2025.
According to officials, the 5.8km line from Kolathur to Nathamuni is the only underground stretch on corridor 5 from Madhavaram to Sholinganallur. CMRL has invited bids to construct the underground line with twin tunnels for the upline and downline and link it with five underground stations at Kolathur junction, Srinivasa Nagar, Villivakkam suburban station, Villivakkam bus-terminus and Nathamuni. Deadline for completion of the line is 3.8 years.
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 conditions.
The soil type 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 keep the vibrations while drilling to a minimum because it may otherwise affect nearby buildings. Tunnels on this stretch are going to be built at a depth of 15m to 21m.
In January 2021, only one firm bid for the construction of this stretch when CMRL floated tender for the line for the first time. Officials said the bidder also quoted more than CMRL’s estimate. Hence the bid had to be cancelled. “The bidder’s quote was nearly 60% more than our estimate. So, we had to cancel the tender,” an official said.
Meanwhile, towards the end of December a first test pile (foundation pillars for elevated corridor) was bored on the 11.6km Puzhuthivakkam-Sholinganallur stretch on corridor-5 from Madhavaram to Sholinganallur. The stretch will have 11 elevated stations.
The stretch connects localities like Madipakkam, Kovilambakkam, Medavakkam and Perumbakkam that are otherwise poorly linked by public transport. CMRL officials said this stretch will be part of the elevated corridor which they are expecting to be ready by 2025. Construction of an elevated line started on the Porur-Poonamallee stretch last year.