Chennai Metro Rail’s TBMs to begin tunneling between Thiruvanmiyur and Indira Nagar for phase II project in November

Chennai Metro Rail is all set to start tunnelling work in one of the most challenging stretches for the upcoming phase II project between Thiruvanmiyur and Indira Nagar in November.

Two tunnel boring machines (TBM) will create twin tunnels for a distance of nearly 650 metres between Thiruvanmiyur and Indira Nagar.

In the 118.9 km phase II project, corridor 3 from Madhavaram to SIPCOT via Adyar whose length is 45.8 km has a significant portion of underground network of 26.8 km; one of them is the Thiruvanmiyur to Indira Nagar stretch. In a few years, trains originating from Madhavaram will take commuters through at least 40 locations including Thiruvanmiyur and Indira Nagar before reaching SIPCOT.

Officials of Chennai Metro Rail Limited (CMRL)said they have been excavating for a few weeks now at Thiruvanmiyur station site; while one of the TBMs have been lowered, the other will be done soon. 

The major challenge now is excavation of the site due to the presence of hard rock. “We did expect to encounter hard rock at Thiruvanmiyur but didn’t foresee that it would be such high-quality hard rock like granite. Initially, the contractor planned to carry out controlled blasting to break them and complete the excavation. But as a better alternative, the contractor chose to use chemicals and disintegrate the hard rock,” an official said.

CMRL officials added they are currently excavating at a depth of 22 metres at Thiruvanmiyur. Owing to the presence of hard rock, the tunnelling work too may be quite slow in this 650-metre stretch between Thiruvanmiyur and Indira Nagar. Ideally such a short stretch can be completed soon, but officials expect that it may take nearly a year for the machines to create twin tunnels. 

“If the machine constantly drills through hard rock, the cutter head discs of the TBM will wear out soon and we will have to carry out a process called cutterhead intervention and change the parts. Cutterhead intervention may have to be done several times for both machines along this stretch and could be time consuming,” an official said.