CHENNAI (Metro Rail News): Chennai Metro Rail Limited (CMRL) is going to build deeper and smarter stations. The concourse level and two tunnels for two lines will be stacked one above the other. The facility will be as deep as Central Metro at 28m to 30m, but less than half its length at 157m and one-fourth its width at 9m.
CMRL has decided to go with underground stations with a stacked-up platform design to save the cost of land acquisition at locations where the width of the roads are as narrow as 10m. Such stations could also be built faster and may cause less public inconvenience. A metro rail official said they have identified Pattalam, Perambur, Doveton, and Thirumayilai for such facilities.
Another four stations are being planned on corridor 4 from Light House to Poonamallee which will cut across Mylapore, T Nagar, Nandanam and Vadapalani.
An official said, “Why spend huge amounts of money to acquire properties and trouble people? Instead, we decided to optimize the space available and go deeper underground”.
All 128 stations in the 118.9km phase-2 planned may look and feel different from one another as CMRL is now simulating site conditions and projected ridership to generate a unique design for every station. Construction for the phase is expected to begin by June 2020 with a 52km taken up first and is likely to be ready by 2024-25.
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At present, soil tests are being completed and detailed design for the stations is underway.
Compared to the standard station design that CMRL followed in the 45km phase-1, the detailed design consultants are now using computer simulation software to generate unique designs for each station based on the site condition and projected ridership. “In Pattalam and Perambur, the roads are as narrow as 10m or 11m. If we have to build stations like those in phase-1, we may have to acquire properties on either side of the road.
Also, at some locations, the daily footfall may be less than others. So, instead of cut-and-paste design, we will build according to our requirements,” a metro rail official said.
The stacked tunnels design is nothing new for Chennai. CMRL attempted the design in Central Metro, where two twin tunnels were built on two decks complete with a ticketing level on top. The mixed soil conditions with loose soil top and rock below, however, posed a huge challenge and CMRL took nearly six years to complete.
But soil tests conducted along corridor 3 between Madhavaram and Sholinganallur showed mostly loose soil up to 10m and charnockite rock below or clayey soil on top with the rock below. A top metro rail official said “Soil conditions are favorable. We have done a thorough soil for every 25m to 50m, so even if we come across rocks, we will use rock-cutting machines instead of tunnel boring machines”.