The Chennai Metro Rail Limited has started constructing shafts for launching Tunnel Boring Machines in three locations – Washermenpet, Shenoy Nagar and Nehru Park.
While an initial batch of two TBMs arrived from China in the second week of December, two more arrived last week. A total of 11 TBMs would eventually be involved in the construction of the city's underground metro network.
CMRL Managing Director K. Rajaraman said that since tunnelling work cannot be put on hold till underground stations start taking shape, vertical shafts that go to a depth of 20-25 metre are being built to lower the TBMs. “These shafts would eventually be integrated into the station itself. For now, concrete walls would be built to serve as an enclosure for the shaft. Until the base wall is constructed, there would be some amount of water intrusion and it would be constantly pumped out.”
In some locations, such as near the Madras Medical College, excavation teams hit water just half-a-metre below the ground, a senior CMRL official said. The Chennai Central underground metro station, which is slated to be built at a depth of 25 metre, would be the most distant from the ground level and also the largest.
“Once the shafts begin to take shape, the TBM would be lowered inside as six distinct pieces and assembled underground,” Mr.Rajaraman said.
By April, large-scale traffic diversions would start coming into effect in 20 locations across the city, he added. They would be in place till the fag end of 2015.
The Chennai Metro Rail project has two corridors – Washermenpet to Airport and Chennai Central to St. Thomas Mount. A portion of the metro alignment on Corridor-I, between Washermenpet – Saidapet ramp, and on Corridor-II, between Central and Thirumangalam ramp, runs as underground tunnels. Of the 36 upcoming metro stations, 20 would be underground.
