KOLKATA: Over 250 residents of 18 buildings in Bowbazar in central Kolkata were evacuated from their homes after large chunks of concrete and portions of the buildings began caving in throughout Sunday, allegedly after a tunnel-boring machine of the upcoming East-West Metro hit a water pocket — an aquifer, suspect officials — while passing underneath the Bowbazar area on Saturday evening, disturbing the buildings’ foundations.Following the incident, Metro construction was stopped indefinitely and electricity connections to nearby homes were disconnected as a precautionary measure.The evacuated residents were put up in five neighbourhood hotels.Officials of Kolkata Metro Rail Corporation (KMRC), the implementing agency of the Rs 8,575 crore East-West Metro — which will link Howrah with Salt Lake’s Sector V via the river Hooghly — termed it the “first of its kind ever in the history of Metro railways”, calling it an “accident”. Tunnelling on the 3.8km stretch between Howrah Maidan and Esplanade is over. The last leg of underground tunnelling, the 2.45km stretch from Esplanade and Sealdah, is on.“The boring machine probably hit an unforeseen aquifer, a body of permeable rock which can contain or transmit groundwater. Because of the mishap, water flowing into the machine with an increasingly high pressure from within the soil is causing enormous ground settlement. That has led to cracks in some buildings,” said a senior Metro official.The official said the aquifer could not be assessed during the pre-boring ground survey. However, what was more worrying was that the water gushing into the boring machine couldn’t be arrested till late on Sunday, suggesting more buildings could be affected.“In normal situations, we inject a mixture of concrete and certain chemicals to plug the holes. But this time, no matter how much we pushed the mixture in, it was getting washed out and it was uncontrollable. We tried to control the leakage from 7pm on Saturday to 5am on Sunday. But after we failed to bring the situation under control, we began evacuating the people out of their homes,” said Manas Sarkar, the managing director of KMRC.Residents were furious with the Metro authorities, asking why they were not alerted about the situation earlier that caused a situation that forced them to leave their homes in haste and made them see some portions of their homes turn into dust in front of their eyes.“Around 7pm on Saturday, I realised my house was shaking and cracks were developing on the walls. I quickly called in the Metro engineers, who initially tried to make me understand that my house was still fit and there was nothing to worry. But then, the marble on the ground floor room cracked in front of them. That alerted them and they began making phone calls, asking their seniors to stop the tunnel-boring,” said Goutam Laha, a resident of Durga Pithuri Lane.Laha and his family were evacuated from their homes around 2am on Sunday, when cracks filled the pillars and walls and the 200-year-old building started to tilt. On Sunday morning, he saw a large portion of the building cave in while he was made to wait at the mouth of the alley, watching his home turn to dust.TOI found at least four buildings, all several decades old, large portions of which had caved in on Sunday. There were at least 20 other buildings on BB Ganguly Street, Durga Pithuri Lane and Shyakrapara Lane, which seemed severely affected with large cracks dotting the walls, floors and terraces and portions of concrete and dust coming off every now and then.A large team of Kolkata Police, the fire department and the disaster management group were posted in the area, blocking the alleys, calling out residents of adjacent lanes out of their homes and moving around with loudhailers, preparing residents to leave their homes and shift elsewhere, if needed.“We understand residents were forced to leave their houses in haste. We will set up a control room in the area and will ensure complete safety. We have also formed a team of engineers, who will inspect the other households in the area before reinstating electricity,” said mayor Firhad Hakim.The mayor added that KMC authorities have held detailed discussions with Metro authorities, who have agreed to foot the hotel bills for the residents for the next 3-4 days before settling them in flats in the city. “Meanwhile, we have asked the Metro officials to take help of experts recognised by KMC to check whether the affected houses can be rebuilt. If yes, Metro will rebuild those. In case it is not feasible in this part of the city, they will make buildings for them somewhere else,” Hakim said.