Metro and Calcutta Municipal Corporation have twin tasks at hand: to decide whether a letter was sent and whether the subject of the missive took place at all or not.

Stretches along CR Avenue, under which the North-South Metro lines run, have subsided, creating uneven patches, according to a civic official. The ride on these stretches along CR Avenue is “very bumpy”, the official said.

The Calcutta Municipal Corporation had written a letter to the Metro authorities, seeking permission to inject concrete under the ground along CR Avenue to prevent such subsidence, the official added. “We wrote to them about three months ago but they did not respond.”

Metro Railway, however, denied having received any letter. “Neither have we received any official letter from the civic body on subsidence nor do we have any report on subsidence along CR Avenue,” a Metro official said.

A CMC engineer said the civic body had identified some areas along CR Avenue where the road had become uneven. The road has subsided on multiples stretches, the engineer said.

So, what is the reason behind the purported subsidence? The civic engineer said there were no tunnel-boring machines when the North-South Metro was built in the 1970s. Roads were dug open to build tunnels through which trains now run, he said.

Once the tunnels were completed, there was a gap of about 20ft between the concrete structure of the tunnels and the road, he said.

“This gap was filled with rubbish, sand and soil. In places where the material has become more compacted over the years, the road has subsided,” the civic engineer said.

He said water leaks could also be a reason behind the subsidence.

The civic official said the CMC wanted to inject concrete to fill the vacuum created because of the compaction.

“We want to stop the subsidence of the road, for which we need to inject concrete and other chemicals,” the official said.