Chennai Metro Phase II: Tunnelling Work On Thiruvanmiyur–Indira Nagar Stretch Likely To Begin In November

The Chennai Metro Rail Limited (CMRL) is preparing to begin tunnelling operations in November on one of the most technically challenging segments of its Phase II expansion project — the stretch between Thiruvanmiyur and Indira Nagar, The Hindu reported.

Two tunnel boring machines (TBMs) will soon start creating twin tunnels spanning around 650 metres between the two stations.

This work forms part of Corridor 3, a 45.8 km line extending from Madhavaram to SIPCOT via Adyar, which includes an underground section of 26.8 km.

Once completed, this corridor will connect commuters from Madhavaram to SIPCOT, covering nearly 40 key locations, including Thiruvanmiyur and Indira Nagar.

CMRL officials said that excavation work has already been underway for several weeks at the Thiruvanmiyur station site.

One TBM has been successfully lowered, while the second is expected to follow shortly.

However, engineers have encountered significant challenges due to unexpectedly hard geological conditions.

“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,” a CMRL official was quoted as saying by The Hindu.

Currently, excavation has reached a depth of 22 metres.

Officials noted that the presence of dense granite formations will likely slow tunnelling progress considerably.

Although such a short stretch would typically be completed swiftly, the twin tunnel construction could take up to a year to finish.

“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,” the official added.

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