Workers break up the collapsed Ultadanga flyover slab on Friday. Picture by Amit Datta

Work started on Friday to break up the portion of the VIP Road flyover that had collapsed on March 3 and remove the parts from Kestopur canal so that the water flow is restored before the onset of monsoon.

“Machines are being used to peel the concrete off the deck slab and break the steel structure into small pieces. The broken pieces are then being pulled by a crane to a makeshift dump on a bank,” said an official of the city-based Royal Steel Company, which has been tasked with removing the collapsed structure.

An official in the CMDA, which has engaged the company for the work, said a block in the Kestopur canal could affect the tidal flow of water from the Hooghly, leading to deposition of silt, causing the canal to overflow during monsoon.

A CMDA engineer, who was at the site in the afternoon, said the work could take more than a month.

A team of 20 is on the job. “The workers are drilling a hole on the concrete with the help of sledgehammers. Then the drilling machine powered by the concrete compressor is digging deep into the base of concrete through the hole and breaking the slab,” said a company official.

“We are using ropes to tie up the slab so that the broken parts do not fall in the water,” added the official.

Winch machine — a machine with electric wire rope — will be used to pull chunks of concrete or steel that might fall in the canal during dismantling, according to the official.

The other set of workers are using gas cutters to break steel plates into smaller pieces — each weighing between a tonne and a tonne and a half. Gas cutters are also being used to unhinge joints before breaking the girder into fragments that can be removed separately.

Oxygen cylinders and LPG cylinders are being lifted atop the collapsed portion with the help of a crane to power the gas cutters round the clock.

“We have begun work from two edges of the collapsed structure and will move towards the middle,” said the official.

Experts from the JU civil engineering department, Arup Guha Niyogi and Dipankar Chakravorty, engaged to probe the flyover crash had suggested to the CMDA, which was at a loss about how to free the canal, that shear the slab off concrete would reduce its weight by half and allow it to be lifted.

In their report in late March, JU experts had stated that the metal and concrete from the collapsed structure could not be used again, prompting the government to focus on removing the deck slab from the canal.