50 FEET UNDER YOUR STREET
Tunnelling Work On Metro Set To Start At Nehru Park For Chennai Central-St Thomas Mount Corridor By Month-End.
Agiant tunnelling machine sits at the bottom of a wide shaft that is deep enough to swallow a fivestorey building (50-60 feet high) in the middle of Poonamallee High Road near Nehru Park. Lowered with a crane that can lift 400 tonnes, the machine’s blackdiamond-linedspiralcutter head has been placed against the concrete wall of the shaft from where it will start boring into the ground under the city
When it’s done, the machine will emerge from the earth, cutter head first, in a similar shaft in Egmore.
More components of the machine will be lowered into the shaft and assembled in the coming days so Chennai Metro Rail Ltd can start the tunnelling work by the end of this month or early July. The tunnel boring work will start at Nehru Park for the transit system’s Chennai Central-St Thomas Mount corridor.
Preparations are underway to start tunnel boring at sites in Egmore and Kilpauk and near Pachaiyappa's College.
The machine is capable of cutting through rock and hard soil. Metro officials said they needed the best equipment because the soil under the city is hard and rocky atdepthsbelow 13 metres. Tunnel boring machines consist of various parts including the cutter head that can be fitted with different blades according to the soil condition, a screw conveyor that removes soil and rock, a hydraulic thrust cylinder that holds the machine in place as it bores and moves the machine forward, a pressurised chamber for mechanics to enter the machine and several gantries that run on rail track and carry pieces of the precast concrete tunnel walls. Rail track has been laid inside the shaft for the gantries and a locomotive will transport pieces of the concrete tunnel lining.
Most of its operations are automatic though more than 100 trained personnel will control its working from a computerised operations centre.