Underwater tunnel in Metro Phase II

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. 

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 3 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

tones with a length of 110 meters including its backup gantries, the

machine has been at work nearly 20 meters below the ground and

subsequently under the river, for several months now.

It has drilled 1,050 meters so far, crossed the river and slowly drilling

its way to Adyar Junction station.

As one step into the tunnel, the presence of a large yellow ventilation

duct is unnoticeable; 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 cutters head an important component

of 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.

As one approaches closer to the massive machine, a locomotive train

with huge barrels carries the soil and muck from the machine and

transports it to the ground for disposal.

“The machine has drilled underneath petrol pumps, a college and a

river. We are eagerly awaiting its completion next month,” he says.

And soon after that, there will be another job waiting for the machine

in another part of the city, to create another tunnel.