Chennai Metro to bore beneath existing tunnel at Nandanam station

Chennai Metro to bore beneath existing tunnel in Nandanam

Chennai Metro Rail Limited (CMRL) is set to undertake a complex tunneling operation beneath an existing operational tunnel near Nandanam station. This will be the first time the city’s metro network attempts such an underground crossing.

The new tunnel is part of the Phase 2 corridor connecting Madhavaram to Sholinganallur. The existing tunnel currently serves the Blue Line between Chennai International Airport and Washermanpet.

Why this operation is different

Tunnel boring machines (TBMs) have been used extensively in Chennai’s metro construction. But boring directly under a live tunnel adds a layer of risk.

Engineers will have to monitor ground movement and structural stress continuously. The existing tunnel will remain operational during the work, though CMRL has not yet confirmed whether train services will be curtailed.

Officials said the vertical clearance between the two tunnels will be about four to five metres. The new tunnel will be at a depth of around 25 metres below ground level.

Part of the larger Phase 2 push

CMRL’s Phase 2 project spans over 118 km across three corridors. The Madhavaram-Sholinganallur line is one of the key stretches aimed at decongesting the city’s road network.

This particular section between Nandanam and Saidapet has been challenging because of the existing underground infrastructure. Water mains, sewer lines and utility cables run close to the alignment.

Earlier this month, CMRL completed tunnelling on another stretch near Teynampet without major disruption.

What happens next

The boring work at Nandanam is expected to take about two months. Once completed, the tunnel will be lined with concrete segments and equipped with rail tracks and electrical systems.

CMRL plans to open the Phase 2 corridors in phases between 2028 and 2030. The Nandanam crossing is a critical milestone for the southern leg of the network.