Delhi metro tunnels its way South

Express news service

Tunnel Boring Machine: A TBM is a machine that has a circular cross-section and is meant to excavate a smooth tunnel without disturbing the soil around.
* While the blades of the head of the machine that cuts its way through are called diamond cutters, the machine also helps fix the the concrete rings called segments along the tunnel. The mud dug out is sent to the end of the machine through a conveyor belt going up above.
* A TBM can dig up to 250 metres in one month and about 10 metres in one day.
* While a TBM costs around Rs 20 crore, a typical TBM is fabricated over a period of 8-9 months and is assembled within four weeks on the site.
* The system is operated electronically and tunnels its way through a pre-determined route fed into the machine operating it.
* The system is heavy on power and needs about 11 KW at one go.
* The average workforce around the TBM consists of civil engineers, electrical engineers, mechanical engineers, electricians, mechanics, crane operators, ring drivers and other workers.
* When the machine is at work, the tunnel can get warmer than 50 degrees Celsius. As a result, chilled area called refuges are created and big fans and ducts are set up to keep the air clean and cooler.
* While Phase I had to deal with tough and hard rocks near Chawri Bazaar, Phase II will be dealing with a soft ground. Metro is using the Earth Pressure Balance TBMs supporting the soft ground without disturbing the residential pockets.
* Phase I of the Delhi Metro used only two TBMs previously used in Taipei and Bangkok.