The East West corridor metro project is underway in Kolkata which saw a milestone on Monday, with the completion of the deepest Metro ventilation shaft in India. The base slab of the escape shaft is 43.5m below ground level, equivalent to a 15-storey building.
Kolkata got its first-ever underwater twin rail transportation tunnels and the deepest underground metro station from Howrah Metro station which surpassed Hauz Khas and Chawri Bazaar Metro stations in New Delhi. The project is a joint effort of Afcons and KMRC are meant to provide ventilation to the tunnels, but also for evacuation during an emergency.
The evacuation shaft is located at Strand Road near river Hooghly and is situated between the two tunnels. At Howrah Metro Station, from where the tunnels start entering the river, the tunnel invert is 30m deep. From there, the tunnels go deeper till 37m invert level while crossing the riverbed. The Diaphragm Walls had to be constructed 56m deep from ground level as per base demand of the geometric profile of tunnel alignment. This necessitated the ventilation shaft to go as deep as 43.5 metre.
The Metro shaft has been constructed adopting innovative engineering techniques and methodology to navigate geological challenges and overcome any impact on Kolkata’s circular railway track along river Hooghly," said Satya Narayan Kunwar, Project Manager, Afcons.
The shaft is located very close to the river which resulted in ancient alluvial deposition, river course transformations and varying foundation data of old buildings at the location. Due to the erratic subsoil deposition, a detailed study was conducted for soil mapping. Large number of borehole investigation data was utilised and analysed for generating soil profiles in the Gangetic plain.
Kolkata has the oldest metro railway service in India which connect the north and south of the city.
The metro line also saw expansion reaching the far flung southern fringes of the city in recent years.
The East-West metro project has 17 stations spanning 22km and aims to connect Howrah in the East and Teghoria in the West, with a portion of the line running under the Hooghly river. 11 stations are elevated and 6 of them are underground. This will also connect two business districts like Salt Lake and BBD Bagh and two railway stations of Howrah and Sealdah. The first phase between Salt Lake sector 5 and Salt Lake stadium was inaugurated by Union Railway Minister Piyush Goyal in February 2020.