Transforming commute: First glimpse of underwater tunnel in Chennai Metro Rail’s phase II project connecting Greenways Road to Adyar

The Hindu provides an exclusive look at Chennai Metro Rail's underwater tunnel construction beneath the Adyar River.

As vehicles zip past one of the busiest areas of the city, the Adyar bridge, a 500-tonne gigantic machine operated by a bunch of workers quietly drills the earth. Under this bridge, tunnels are getting ready well beneath the Adyar River. In a couple of years down the line, trains will zip past these twin underwater tunnels and those driving their vehicles over the bridge may opt to skip the traffic and take a ride below, in the train. 

The Hindu gives you the first glimpse of one of the underwater tunnels built by Chennai Metro Rail for the upcoming phase II project. Of the twin underwater tunnels created between Greenways Road and Adyar Junction, one tunnel constructed by the Kaveri tunnel boring machine (TBM) has been completed and the next TBM named ‘Adyar’ will reach the Adyar Junction (near Theosophical Society) by January 2025. This stretch is a section of corridor 4 of the phase II project and once the work comes to an end in a couple of years, a commuter taking a train at Madhavaram can travel via this underwater tunnel at Adyar and head all the way till SIPCOT in Siruseri.

The Adyar TBM is a rather special machine. After creating a tunnel for Chennai Metro Rail’s phase I project, it is once again back in the phase II project, after going through refurbishments. Weighing close to 500 tonnes with a length of 110 metres including its backup gantries, the machine has been at work nearly 20 metres below the ground and subsequently under the river, for several months now. It has drilled 1,050 metres so far, crossed the river and slowly drilling its way to Adyar Junction station.

As one steps into the tunnel, the presence of a large yellow ventilation duct is unmissable; it helps to pump in fresh air into the system and maintain the ventilation. “We also have wifi inside the tunnel for quite a distance to ensure we can communicate well,” an official of Chennai Metro Rail Limited says.

One of the key challenges in constructing a tunnel between Greenways Road and Adyar Junction was the presence of soft rock and hard rock. “We had to make as much as 98 cutter head (an important component of a TBM) interventions. The TBM moves very slowly drilling through rock,” he adds.

Sporting helmets and jackets, there are about 50 workers at the Greenways Road site. While nearly 30-35 workers are engaged in different jobs, a dedicated 15-member team operates the TBM, gauging the speed, its alignment, the geology through which it bores and monitoring the sensors to check if there is presence of any poisonous gas.

“Water from the river cannot enter the machine, because we have made meticulous arrangements for protection. But in some of the countries abroad, there have been instances of river water ingress into the tunnel,” he says.