Calcutta: Two gates of Raj Bhavan have been fortified with steel rods, cement and pieces of wood to prevent any possible damage to the British-era structures from the tunnel boring machines of the East-West Metro.

The twin tunnels of the Metro are coming up beside the boundary wall of the Raj Bhavan at Government Place East. The Howrah-bound tunnel will be about 18m inside the wall while the Salt Lake-bound tunnel will be about 7m inside, an engineer said.

The two tunnel boring machines are now 22m below the ground.

"The gates are important structures and we have provided support to ensure there are no cracks when the boring machines pass near them. When the tunnels are dug there can be settlements leading to cracks," an Afcons official said.

The company is building the twin tunnels between Howrah Maidan and Esplanade.

The main concern for the engineering team is the safety of the arches. "The arches add to the aesthetics. If disturbed, they can be vulnerable," an engineer said.

At present, the Howrah-bound tunnel is being dug under the Raj Bhavan campus while the machine digging the Salt Lake-bound tunnel has been stopped about 140m away. "We expect the Howrah-bound machine to cross the Raj Bhavan campus by next week. In the first week of March, we plan to start the second machine towards Raj Bhavan and by the middle of next month it should cross the area," an Afcons official said.