BENGALURU: It was a journey like no other that Bangalore Metro Rail Corporation Limited’s Tunnel Boring Machine (TMB) Lavi had to undergo before it could call it a day. It had to be interrupted nearly 200 times before it completed its 14-month trip on Saturday at MG Road, exceeding the deadline by two months. Extremely tough rocky conditions, shortage of oxygen for infrastructure projects due to Covid and manpower shortage were a few of the issues it faced drilling on inch by inch from Shivaji Nagar, after it was launched on February 10, 2021.
Speaking to The New Indian Express on the enormous challenges encountered, a senior Metro official said, “The biggest issue faced when carrying out work using any TBM is the damage to the discs on the cutter head. In case of Lavi, the discs were damaged more than that encountered with any TBM before. For every six metres drilled, four discs get damaged for any machine when passing through regular granite. But since it had to pass through a long stretch of Dolerite Zone, more number of discs got damaged. This forced us to stop, repair the discs and start again.
This happened nearly 200 times during the course of the drilling the 1076-metre stretch it completed.” Dolerite is soft outside and is very hard at the core. “After some rings are laid, the machine comes face to face with a very hard surface at the core. This causes numerous damages,” he said. The pressure generally applied to break the rocks is 120 Mega Pascal but in the case of Dolerite, a pressure of 180 Mega Pascal had to be used to break them. A team devoted exclusively to set right the broken discs had to be sent to the spot 60 m below the ground.