Infrastructure

Yet another tunnel completed

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As you step inside the underground Metro Rail station at Thirumangalam on Saturday morning, just after a brief spell of rain, the strong scent of wet mud hits you.

About 16 metres below the ground, there is seamless convergence of two skilled engineering structures — the meeting of the elevated Koyambedu Metro station with the underground Thirumangalam station.

The underground station begins like a cave-like structure that gradually leads to two massive holes — the tunnels that will soon see two blue trains zip in and out.

One of the tunnels is punctured. There is a screechy sound, accompanied by white smoke, and a few minutes later, a giant concrete wall collapses. Out comes an 850-tonne tunnel-boring machine (TBM), brought in for the Chennai Metro project from Russia.

The TBM began drilling from Shenoy Nagar in October 2012 and reached Thirumangalam on Saturday. Drilling through the 4.6-km stretch has been challenging due to unpredictable soil conditions, says a CMRL official.

The other tunnel, which a second TBM has drilled through, exhibits the combined skills of Russian and Indian workers as they join hands to build tunnels for Chennai Metro.

Across the city, a total of 11 TBMs are engaged at various Chennai Metro sites.

In the two tunnels, tracks have to be laid and walkways and cross passages created. In the event of an emergency, passengers can take the walkway that runs along the length of the tunnel and use the cross passage to move to the other tunnel. There will be a cross passage every 250 metres to link the two tunnels.

“In case there is a problem in both the tunnels, there are two generators at every station and also a UPS that can run for two hours, if required,” says the CMRL official.

At the four stations along this alignment — Thirumangalam, Anna Nagar Tower, Anna Nagar East and Shenoy Nagar — station work is at various levels of progress.

After the tunnelling is fully complete and the station work is done, Chennai Metro’s operations will extend from the elevated Koyambedu corridor to this underground line.

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Printable version | Jan 20, 2020 3:36:53 PM | https://www.thehindu.com/news/cities/chennai/chen-infra/yet-another-tunnel-completed/article6689434.ece

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