Tunnel Boring Machine (TBM) Bhadra, currently digging a north-bound 1,186-metre-long tunnel from Venkateshpura to KG Halli, is expected to achieve a breakthrough on February 7. Its sister TBM Tunga, which emerged out of KG Halli in December after boring 1,184.4 metres from Venkateshpura, is scheduled to be launched for its next tunnelling assignment between KG Halli and Nagavara on February 1, well-placed sources in the Bangalore Metro Rail Corporation Limited (BMRCL) have told DH.

Bhadra’s breakthrough will be the 22nd out of 24 tunnelling drives to be completed on the 21.26-km Pink Line that will connect Kalena Agrahara to Nagavara via MG Road and Tannery Road. Tunga’s launch will be its third and final tunnelling assignment and the penultimate on the Pink Line. The 24th and the final tunnel will be bored by Bhadra once it’s relaunched after the second breakthrough. The last drive will likely start in late March.

The BMRCL deployed nine machines to bore through 20.99 km on the Pink Line. Seven of these machines (Urja, Varada, Avni, Lavi, Vindhya, Vamika and Rudra) have finished their job.

The final two drives will be completed by the end of this year. The Pink Line’s deadline is March 2025.

As of January 30, Bhadra has tunnelled 1,120 metres out of the 1,184.4 metres (3.35 metres/day) through rock, soil and a mixture of both, constructing 800 out of the 840 rings.

A tunnel ring is made of reinforced concrete and its width is 1.4 metres. Tunnel rings form the concrete base upon which metro rail tracks are laid.

Tunga, which achieved its second breakthrough on December 6, 2023, is ready for its next mission. While it takes 45 days to relaunch a TBM after its breakthrough, Tunga took more time to launch because of the extensive welding required for its cutter head, the sources said.

“Welding not only costs money, but is also time-consuming. The contractor (ITD Cementation India) will bear the additional cost,” the sources said. Except for a minor work about a displacement cylinder, all preparations have been completed for relaunching Tunga, the sources added.

The construction of the Pink Line’s 12 underground and six elevated stations is in advanced stages. Texmaco Rail and Engineering Ltd has started laying tracks between the Cantonment and Venkateshpura stations.

As per the BMRCL’s January 2024 newsletter, 29.27 per cent of track plinth casting has been completed on the elevated section (Kalena Agrahara-Tavarekere) and 0.079 per cent on the underground section (Taverere-Nagavara).