The geology of Chennai is a cause of sleepless nights for engineers who are working day and night to build the underground passage for Chennai Metro Rail.
Chennai Metro Rail General Manager (construction) V Somasundaram says the underground stretch is a challenging task for engineers as the ground is a mixture of soil and rock, unlike in other metros where the ground is either soil or rock. “In Delhi it is totally soil but in Chennai it is both soil and rock, which poses a big challenge for tunnel boring machines (TBM).”
He said the stretch between Washermenpet and Mannadi was totally soil, allowing the TBMs to burrow smoothly. Overhaul and repair of the machines was done only once. However, the same cannot be said of the stretch between Nehru Park and Egmore, which is half rock and half soil, posing a huge problem for the machines. “The TBMs have had to be overhauled and repaired twice. And we expect them to be overhauled twice more soon,” says Somasundaram. Another major issue is the presence of water. The underground stretch is full of water, posing another challenge, he says.
But will this delay the work in the underground stretch? “No,” says Somasundaram. He says Metro Rail had already taken note of all these issues before starting work. “We have zeroed in on an average speed of 10 metres per day. Sometimes we go at a speed of 15-20 metres and at other times only five metres. All this has been factored into the schedule,” he says.
The first TBM from Washermenpet and Mannadi has completed the 1341.2-metre drive and reached Mannadi, while the second on the same stretch has completed 203 metres. On the stretch from Nehru Park to Egmore the first TBM has completed 360 metres and the second TBM 475 metres.