Excavation for setting up the underground Howrah station of East-West Metro, which will be India’s deepest station at 100ft below the surface, has just ended 13 months after it started.

Work on building the station across 40,000sqm has begun following demolition of the walls of a 200m stretch of the two tunnels of the project, which will link Howrah Maidan to Sector V.

The walls have been demolished to make room for the station, said officials involved in what has been touted as the most ambitious infrastructure project of the city.

“The tunnel-boring machines have dug the twin tunnels from Howrah Maidan till Esplanade. The walls of the tunnels on a 200m stretch had to be broken and Howrah station built for allowing passengers to access the station...” said Virinder Kaul, vice-president of Afcons, the construction company that is building the Howrah station of East-West Metro.

In any underground railway project, stations are built before the tunnels are burrowed. “The task becomes more challenging and expensive if it were the other way round,” an official said.

As for East-West Metro, however, land logjam prevented the authorities from building the Howrah and Mahakaran stations before the twin tunnels were bored.

The impasse had resulted from conflicting stands of the railways and the state government over the alignment of the East-West Metro tracks under the central business district.

Engineers said problems related to setting up an underground facility increases with depth. The excavation machines conk out frequently because of lack of air supply.

There are safety issues, too.

“Had the tunnels suffered any damage when the walls along 200m were being pulled down, a large stretch would have become vulnerable,” an engineer pointed out.

To prevent any such damage, struts built with 2,000 tonnes of steel have been installed to support the tunnel walls near the site of the station.

The Howrah station will be at least a metre deeper than the proposed Esplanade station of the East-West corridor.

The base of the station will be at 105ft and the platforms at 100ft below the surface, officials said. The station will have five levels, across 40,000sqm.

“Excavation started in November last year and civil construction of the station, including the platforms, will be complete early next year. There will be three platforms. During rush hours, the doors of the trains will open on both sides,” an official said.

The station will have 39 automated gates, 38 token counters, 28 escalators, seven elevators, 200 ventilation fans and a reservoir that can store 3.5 lakh litres of water for firefighting. Sources said the elevator count might increase.