The 16.6 km-long rapid transit project will connect Kolkata and Howrah. (Representational)
The country's deepest underground rail ventilation shaft equal to a 15-storey building and an important part of the city's East-West Metro line was completed on Monday, officials said.
The ventilation shaft, which is 43.5 m deep, was completed jointly by Kolkata Metro Rail Corporation (KMRC) and Afcons, a private engineering company.
Such shafts are not only used to provide ventilation to the tunnels, but also for evacuation during an emergency.
The evacuation shaft is located on Strand Road near Hooghly river, a statement said.
"The Metro shaft has been constructed adopting innovative engineering techniques and methodology to navigate geological challenges and overcome any impact on Kolkatas circular railway track along the Hooghly," Afcons project manager Satya Narayan Kunwar aid.
The shaft is located very close to the river and abutting with the circular railway which makes its deep excavation very challenging, it said.
The circular railway line runs parallel to the river in stretches.
The 16.6 km-long rapid transit project will connect the twin cities of Kolkata and Howrah.