Chennai Metro Phase II: Work Under Adyar River Set To Begin In September

Starting in September, construction will commence under the Adyar near Greenways Road Metro Station. A tunnel boring machine will be used to dig a 400-metre-long tunnel, going 20 metres under the river.

In February, the tunnel boring machine (TBM) named Kaveri began its excavation under the RA Puram corporation playground. Currently, it is 120 metres away from the river.

Once finished, the tunnel connecting the Greenways Road Metro Station to the Adyar Junction Station will span a distance of 1.2 km.

According to an engineer at the site, the TBM is currently boring at a speed of 1.5 metres per day. This slower pace is necessary due to the presence of various structures above the road, such as a petrol bunk and a college. Operating the machine at a higher speed could potentially cause cracks and damage.

The TBM will continue its underground journey, passing under Durgabai Deshmukh Road and crossing the Adyar River near Thiru. Vi.Ka Bridge, before reaching the station being constructed at Adyar Junction.

According to the engineer, the speed of the TBM may slow down to 1 metre a day when it enters the riverbed, reports Times Of India.

Tunnelling under a water body can present challenges, as experts have pointed out.

During the planning stage, the water pressure in the river is taken into consideration. The tunnel wall will have a thickness of about 35 cm, but if the pressure beneath the river is higher, the thickness may be increased to 40 cm or 45 cm.

To prevent water seepage, the tunnel boring machines also waterproof or seal the gaps between segments and rings in the tunnel, as explained by R Ramanathan, a former official of Chennai Metro Rail Limited (CMRL).

The crown or top of the tunnel, will be situated 7 metres below the riverbed, as stated by T Archunan, the project director of CMRL.

The stretch between the Greenways Road Metro Station and the Adyar junction is a part of Corridor-3, which spans 45.4 km from Madhavaram Milk Colony to Siruseri Sipcot.

Phase II comprises three corridors: Madhavaram to SIPCOT (Corridor-3), Light House to Poonamallee (Corridor-4), and Madhavaram to Sholinganallur (Corridor-5).

According to M A Siddique, the managing director of CMRL, Phase II, covering a distance of 116.1km, is expected to be opened to the public in stages between 2025 and 2028.

Phase II of the metro project will include the construction of tunnels not only under the Adyar River but also under the Chetpet Lake.

Currently, preparations are underway to set up a launching shaft at the Chetpet Metro Station site for the tunnel boring machine, which is scheduled to arrive in September, as per officials.