The second Tunnel Boring Machine (TBM) to be used for excavation at Nehru Park metro station will begin operations by October 15.

The first machine which was launched in late July has already covered about 84 metres, sources said. The two TBMs will have to cover a stretch of 939 metres from Nehru Park station to Egmore station.

At present, the first TBM has been drilling at the rate of about two metres a day. But after October 5, the speed of the two machines would gradually be increased to three to four metres and four to five metres a day, respectively.

“We are slowly speeding up the process because there is a need for some modification before the second TBM starts operating. For instance, the cutter disc which cuts through the hard rock requires to be modified,” said officials.

Also, there needs to be a minimum gap of 100 metres between the two TBMs as a precautionary measure, he said. Both the tunnels are expected to reach Egmore by the end of January. Soon after the tunnelling is over, the levelling concrete will be laid prior to the laying of the tracks. The concrete will be laid for at least a length of five metres from Shenoy Nagar to Egmore.

So far, 1760 of the 5,600 rings to be used for the tunnels have been cast in the factory at Vayalanallur.

To make way for the tunnelling, about 80 borewells on the stretch between Shenoy Nagar and Egmore had to be closed. Each borewell was then moved to places close to their original locations, sources said.

“We ensured that none of the residents were affected by the shifting of the borewells. Since each borewell has only been shifted slightly, it hasn’t created any problem at all,” said a source.

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