Bangalore Metro Rail Corporation Ltd. (BMRCL) has deployed another tunnel boring machine (TBM) to burrow tunnels between Minsk Square and BRV Parade Grounds even as tunnelling work is progressing well between Central College and Vidhana Soudha underground metro stations.

An earth pressure balance (EPB) TBM has been deployed from the Cubbon Park underground metro station site towards BRV Grounds and about 70 m of tunnel has been dug, said Subrahmanya Gudge, Deputy Chief Engineer (Underground).

The same machine, which commenced work by June-end, will burrow the parallel tunnel towards Cubbon Park Station after reaching BRV Grounds, he said.

Mr. Gudge was interacting with journalists from The Hindu who were taken on a visit to the underground tunnel site here on Saturday.

Two slurry-based TBMs, Helen and Maragarita, which have completed tunnelling work between Majestic and Central College, are moving towards Vidhana Soudha. While Helen has burrowed about 400 m of tunnel, a little ahead of K.R. Circle, Margarita has burrowed about 70 m of the total distance of about 724 m. Helen is likely to reach the Vidhana Soudha site by October-end, Mr. Gudge added.

Rocky terrain

Asked to compare the pace of tunnelling work between the stretches of Majestic-Central College and Central College-Vidhana Soudha, Mr. Gudge said that the former appeared to be a little faster than the latter. The underground strata mainly comprised soil in Majestic-Central College stretch whereas it has been rocky towards Vidhana Soudha.

The strata was rocky in the Central College underground station premises too, said R. Balasubramanian, Senior Resident Engineer, representing General Consultants of the underground project.

As much as 80,000 cubic metres of rock has been excavated from the site and a little more is left to be removed, he said. From March 2011 till now about 1,350 controlled blasts have been carried out to remove rocks. At the Vidhana Soudha underground station site, the presence of rocky strata is little less and about 30,000 cubic metres of rock have been excavated, he said.