Boring on metro tunnel below Adyar River complete

The work on the first of the twin tunnels from Greenways station to Adyar junction covering 1.2 km was

completed after a grueling 178 days. This will be a major boost for the work being carried out in

corridor-3 of Chennai Metro under the second phase

The work commenced in Feb 2023 and both tunnels need to pass below the Adyar River for a distance of

300m. Two earth pressure balancing (EPB) tunnel boring machines - nicknamed Kaveri and Adyar - were

engaged for the work. Kaveri has successfully completed the tunneling drive, while Adyar is currently

277m away from the shaft located at Adyar junction, and expected to reach in Nov.

The tunnels are at a depth of 15-22m, and the walls have a thickness of 35-40cm. This will connect

north-eastern suburbs and core city areas with the IT corridor on Old Mahabalipuram Road, linking

Perambur, Chetpet, Nungambakkam, Thousand Lights, Royapettah, Mandaveli, and Madhavaram.

The tunnel has mixed geological conditions, with the bottom being rocky and the top being sandy. There

was also hard rock below some portions of the Adyar River, resulting in replacement of 65 cutters.

According to sources, tunneling under a water body is challenging because of water pressure.

The boring machines have passed under a few petrol bunks, MGR Janaki College, Andhra Sabha Hospital,

Durgabai Deshmukh Road After a grueling battle to cut through rock, Chennai Metro Rail has finally

completed building an underwater tunnel connecting Greenways Road with Adyar

As part of the Rs 63,246-crore phase II project, Chennai Metro Rail commenced the work to build an

underwater tunnel from Greenways Road to Adyar in February last year, and the earth pressure

balancing tunnel boring machine (TBM) named ‘Kaveri’ was set in motion. The other TBM, ‘Adyar’, is set

to each Adyar station in two months and has another 277 meters left to hit the target.

This short stretch of 1.2 km between Greenways and Adyar falls under corridor 3 of the phase II project,

starting point is Madhavaram and end point is SIPCOT, and covers 45.4 km. According to officials of

Chennai Metro Rail Limited (CMRL), it took almost a year and a half for the TBM Kaveri to bore under

the Adyar River and land at Adyar station owing to difficult ground conditions

Though the machine bored under the Adyar river for a length of 300 meters, it was quite a laborious

process as it was faced with hard rock. This aside, there were also some parts wherein the machine had

to wade through mixed geological conditions like handling hard rock and sand.  The TBMs tools had to

be changed intermittently as a result. There were 65 cutter head interventions (replacement of cutting

tools) and this took as many as 178 days. 

The TBM Kaveri has bored under Dr. MGR Janaki College, a few petrol bunks, Andhra Mahila Sabha

Hospital, Durgabai Deshmukh Road, and Adyar bridge ramp. Officials had previously spoken about the

difficulties of drilling under mixed geological conditions and how it slowed down the TBMs. CMRL has

also been executing underground work in other sections of corridor 3 for the phase II project.