As the city gets ready to witness massive tunnelling operations for the next few years for the 118.9-km phase II project, Chennai Metro Rail Ltd. (CMRL) plans to deploy two specialised machines for handling some portions of the underground work.
This is because the transport utility is anticipating some challenging geological conditions and plans to use two special tunnel boring machines (TBM).
As part of the 45.8-km stretch of Corridor 3 in the phase II project from Madhavaram to SIPCOT, tunnelling work began last week at Madhavaram. It will be an underground stretch till Taramani and will be elevated from there to SIPCOT. “From Madhavaram till Kellys, the soil conditions are definitely manageable. For the first 5-7 metres, it will sandy and then we will encounter marine clay,” said an official.
“Beyond Kellys till Royapettah, the soil conditions start changing gradually; there will be sand, marine clay and some rocky strata too. After Royapettah, the presence of rock underneath becomes more pronounced and at Taramani, it will mostly be hard rock and could be very challenging to carry out tunnelling work. Hence, we plan to use two special TBMs for drilling through rock,” the official said.
Usually, TBMs could bore nearly 10 metres a day but in the presence of hard rock, even these special TBMs can drill only 3-4 metres a day, officials said. While 23 TBMs will be in city for building tunnels, between Kellys and Taramani alone, eight TBMs will be at work to create tunnels and of that, two will be deployed to specially drill through rock.
“In phase II, the stations are built at a depth of 18-20 metres and in a few locations like Mylapore and Taramani, it goes as deep as 25 metres. At Taramani, there will be rock at a depth of 13-14 metres and hence it could pose a major challenge,” he added.
One of the biggest ongoing construction projects in the city is the Chennai Metro Rail work built at a cost of ₹61,843 crore which will link many areas in the north with south and east with west and a substantial portion of this system will be built underground. Apart from the corridor 3, there are two more corridors, Light House to Poonamallee (corridor 4) and Madhavaram to Sholinganallur (corridor 5).
