Six months after a Tunnel Boring Machine (TBM) was lowered at the Mandi House site, the Delhi Metro achieved its third tunnel breakthrough on Tuesday under Phase-III of its construction work.

The TBM emerged at the Janpath metro site, breaking through the north-west shaft after making a 1,516-metre-long tunnel from Mandi House on the ‘Up line’. The TBM made its breakthrough in the presence of Delhi Metro Rail Corporation Managing Director Mangu Singh.

While the internal diameter of the tunnel is 5.8 metres, the maximum depth is 24 metres below the earth’s surface. It took 182 working days to excavate 53,000 cubic metres of earth which was deposited at Mukundpur Depot, the Delhi Metro Rail Corporation said.

A total of 1,083 rings have been inserted simultaneously along with the tunnelling process with each ring having five segments. The tunnel passes under important buildings such as the American Center, Nepal Embassy, Fulbright House, Scindia House, Janpath Market and Jeevan Prakash Building.

The TBM was lowered into the Mandi House shaft on September 25, 2012, and the initial drive began on October 23, 2012. The stations at Janpath and Mandi House are being constructed using cut-and-cover technique, the DMRC said.

Another TBM is working on the ‘Down line’ which is 1,492 metres long and is expected to breakthrough by next month, it added.

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