The action shifts underground

The action shifts underground
Nina C George
Can you ever imagine a civil work in Bangalore without turning the City upside down? Well, thanks to technology, a City notorious for disruptive road cuttings every other day, may soon witness its innards being dug out even as the roads sport a business-as-usual demeanour.

Namma Metro is deploying a cutting-edge technology, for work on its underground stretches. Unlike the Metro's elevated stretches that carry tales of displacement, disruption and devastation, work on the underground stretches will be a smoother affair, thanks to the deployment of Tunnel Boring Machines (TBM).
Tailor-made for digging underground tunnels in busy metros like Bangalore, the TBMs' metallurgy and fabrication are being done in Germany, Spain and Japan. Designed and worked on especially for Namma Metro, the fully computerised machines are believed to cause minimum damage.
“You won't feel any vibration, noise, dust and there'll be no rattling of buildings while the machine is boring into the ground. We get maximum benefit at minimum damage," B S Sudhir Chandra, the director (project and planning), Bangalore Metro Rail Corporation Limited, told Metrolife. Slated to cost Rs 336 crore per kilometre, the 230 meter long and 30 meter wide underground station will be 12 meter below the ground level. The work on the underground metro is billed to commence in April 2008 and end by 2011.
The underground stretch of Namma Metro includes two tunnels, each five-and-a-half meters wide. “We need two tunnels, one for the up and another for down trains. Also in case of a derailment, we can always bank on another tunnel. Services need not be stopped,” explains Sudhir. The tunnels will have an additional cement lining to strengthen and prevent the earth caving in or water seeping into the tunnel.
How the machine works
The 50-meter long TBM will be lowered into a pit that will be manually dug. The boring cutters of the machine will vary depending on the strata—whether rock or soil. The cutter and its design will vary with sand and granite. While the granite machine will cost Rs 40 crore, the sand machine is pegged at Rs eight crore. A cutter for a combination of sand and granite will cost anywhere between Rs eight crore and Rs 40 crore.
"We can bore tunnels up to 12 to 15 meters a day. The machine can complete one km in three months. The 16 km underground tunnel will cost 2.2 times more than the elevated one," explains V Madhu, Managing Director, BMRCL. The cutter will cut and suck the muck which will be transported and dumped at especially marked sites about 20 km away from the City. The civil works of the tunnel alone are slated to cost Rs 110 crores.
Safety measures
Underground tunnels need excellent ventilation, evacuation paths, illumination and good air condition. There will be seven stations underground and Majestic will be the interchanging station. Safety measures underground include CCTVs, swipe cards and evacuation measures. The dependency on overhead electricity is done away with because a Third Rail Conductor running parallel to the rail lines will carry electricity
required for the Metro.
Soil testing
Before the work on the underground Metro begins, the Civil Works Department of the IISc has been entrusted with testing the soil in and around the places where work is marked. "There are many water courses and any change in pressure can alter water courses. We don't want to cause any environmental damage. Hence IISc will study the water courses and the soil and submit a report," says Madhu. Sources at theIISc say the soil testing is complete and results have been submitted to the
BMRCL. The fabrication of the cutters will be done in eight to 10 months.
The global tenders for the underground Metro will be floated by October, and work is scheduled to begin in April. There is nothing to worry, the authorities assure you, for, there will be no disruption.