CHENNAI: The Tunnel Boring Machine (TBM) Palar completed its tunnel drive for 708 metres, including 52 metres beneath the Cooum, and had a breakthrough at the Sterling Road shaft on Wednesday.

As per the Chennai Metro Rail Limited (CMRL), the tunnelling work for corridor 3 in phase II, which runs from Chetpet to Sterling Road, started in September 2023 using two TBMs – Siruvani and Palar.

Siruvani reached the Sterling Road shaft in the downline in August 2024. However, Palar, which began its tunnel drive in January 2024 from the Chetpet shaft in the upline, completed its journey and broke through to the Sterling Road shaft on Wednesday. Each tunnel is 708 metres long.

A particularly challenging segment involved crossing beneath the Cooum River, spanning 52 metres with only six metres of overburden in clay above the tunnel.

“The TBMs navigated beneath significant landmarks, including the Chetpet corporation school, Chetpet dhobi ghat, Karukathamman temple, and various shops along Valluvar Kottam High Road, all without causing any ground settlement. The tunnelling process encountered clay and sand, along with sections of grade V rock,” the press note read.

The tunnelling drive took 260 days to complete, “marking a significant achievement in the ongoing development of the Metro network”.