Automation helps precise work on metro tunnels

Precautions ensure theres no damage to property; rocky ground a daunting challenge

In May 2011, when work for the first underground tunnel for a train in South India was launched, there was more apprehension among Bangaloreans than curiosity.

As the Namma Metro tunneling work between Majestic bus station and cricket stadium, which is part of the East-West corridor, progressed, building owners along the tunnel route via Kempe Gowda Road, Mysore Bank Circle, Old Post Office Road, K R Circle, Dr Ambedkar Veedhi and so on, had doubts about the possible damage to their properties with mega tunnel boring machines (TBMs) operating below.

This is the 17th month since the TBMs started work 60 feet below the ground and around two km of corridor length has been covered along the East-West line.

As promised, the Bangalore Metro Rail Corporation Limited (BMRCL) has carried out the work with all necessary precautions. Till date, no damage has been done to any property along the route, despite hard rocks and rough terrain disrupting the tunneling operations every now and then.

When the Deccan Herald team visited the site of the ongoing tunnel works, between Sir M Visvesvaraya station near Central College campus and the Vidhana Soudha station, the TBM Margarita was busy boring the ground below the K R Circle stretch. Another TBM, Helen, was way ahead boring below the area near MS Building.

Subramanya Gudge, the BMRCL deputy chief engineer (underground), said as many as 80 workers were busy in one or the other task during each shift of tunneling along the East-West corridor. “The corridor has two tunnels of 5.5 meter diameter and they are five metre apart. While the boring instrument of the TBM, fitted with sharp blades, is 11 metre long, the backup system of the machine is 91 metre long,” he said.

BMRCL spokesperson T L Ravi Prakash explained that starting from fixing the alignment for the boring work to the stage of assembling the concrete rings inside the tunnel, every operation is automated and remote controlled.

“The men here do more of the machine control work and are there for back-up. In fact, as we stand inside the TBM, the boring work is on and we move ahead as the tunneling work progresses.

However, since it is a rocky area, the speed of boring is only three mm to four mm per minute. Hence, we are not feeling the movement,” he said. If there is soil ahead, the speed can be accelerated upto 24 mm per minute.

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