Calcutta, April 1: A panel of experts formed by the state government has proposed pulling down what remains of the Vivekananda Road flyover, a part of which collapsed yesterday, in its entirety citing faults in structural design and the use of substandard materials.

The experts said the quality of construction materials used had clearly been "seriously" compromised, partly because of poor monitoring by the Calcutta Metropolitan Development Authority, the executing agency for the flyover.

Formed this morning, the group gave its preliminary impressions within hours. "The committee feels the problems are critical and the entire flyover needs to be pulled down," a senior state government official said.

"The experts have conveyed their findings to the top brass of the state administration. A high-powered committee headed by chief secretary Basudeb Banerjee will take the final call," he added.

Engineers from private firms Afcons and L&T, central government enterprise Rites, and the West Bengal State Highways Development Corporation made up the group. They visited the cave-in site this morning and also examined the stretch of the flyover still standing.

A primary estimate suggests the cost of demolition will be Rs 7 crore to Rs 10 crore, officials said. In 2009, the cost of building the flyover was estimated at Rs 164 crore.

The Telegraph spoke to some of the engineers who had visited the spot and several government officials. They mentioned three major lapses:

Design fault

The experts cited how a one-legged, T-shaped pier supported the stretch of the flyover above the Vivekananda Road-Rabindra Sarani crossing, the spot where the cave-in occurred.

"The flyover is supported by two-legged 'box piers' along the rest of the stretch but, apparently because of lack of space, a single (T-shaped) pier was erected near the crossing," an engineer said.

"The wings of the pier were not strong enough to hold the girders (support beams on which the concrete slabs are placed), and they caved in."

Later this evening, a media release by the state information and cultural affairs department said the flyover had collapsed after "one cantilever (T-shaped) pier of No. 40 had shifted".

The experts cited another structural fault: the bearings of at least three pier caps (which provide a resting surface between the piers and the deck on which the concrete slabs are laid) were damaged.

"The purpose behind placing a bearing is to reduce stress. If the bearings are damaged, it is clear that the design was faulty," one of the engineers said.

The experts also found that the gap between the piers was uneven.

"At the site of collapse, the gap between the nearest two piers was longer than elsewhere along the stretch of the flyover. Such a long gap can be dangerous, making the structure extremely vulnerable," an engineer said.

Poor materials

The experts questioned the quality of the materials used, particularly the steel.

"The basic construction material of the flyover was steel, not concrete. The piers and the girders were made of steel, which needed to be of the highest quality. But primarily, we have found that the quality of steel was compromised," an engineer said.

Later, an official said the group had informed the government that the way the wings of the T-shaped pier had given way suggested that substandard materials were used.

An engineer said the quality of the steel should be tested at a certified lab.

Monitoring gap

The experts said it was clear that the CMDA's monitoring had been slipshod.

"The use of poor-quality materials should have drawn the CMDA's attention --- the agency should have carried out regular checks," an engineer said.

"Government agencies engage construction firms to implement projects, but it is the responsibility of the department concerned to ensure that quality materials are used," a government official said.

Senior officials cited how the public works department had stopped the construction of a bridge over the Kantakhali river in North 24-Parganas after it found that the piers of the bridge had not been built to withstand the expected load.

"The agency was blacklisted and fresh construction had to be started. Had the CMDA followed the same routine, yesterday's tragedy could have been averted," an official said.

The state government today suspended the CMDA chief engineer and executive engineer handling the project.

"None from the CMDA could reply to our questions relating to the agency's inspection regime or the details of the construction, making it clear that there was a lack of monitoring. These two engineers have been suspended as they were handling the project," an official said.