KOLKATA: A 40-mm subsidence of the soil around the Metro work site on Durga Pithuri Lane led to cracks in 18 buildings in the Bowbazar neighbourhood, stated the preliminary report by experts at Jadavpur University that was submitted to Kolkata Municipal Corporation. The report also flagged concern over the fate of ageing houses on Durga Pituri Lane once the Metro services begin. But Kolkata Metro Rail Corporation (KMRC) engineers were quick to allay such fears and said the subsidence incidents were caused during the tunnel construction and would not recur when trains plied the tunnels as hi-tech systems had been designed to absorb vibrations and confine them within the twin tunnels.
“The East-West Metro will run after installing the hi-tech fastening system that will hold the tracks from either side due to which they won’t touch the surface. The same system has been used in London Tube and subway trains in the US,” a KMRC engineer said. International firms have been engaged to install these fastening technologies with elastic properties that can completely absorb vibration. “The best companies will be involved to control rake-induced vibration and take mitigation measures accordingly,” the engineer assured.
According to the JU expert committee, of the 18 buildings that had developed cracks owing to the subsidence a couple of weeks ago, eight were in “catastrophic” conditions. The structures identified in the draft report have been slotted in four categories. The first includes those that have suffered enormous damage because of the ongoing Metro construction. The second category has buildings that need to be monitored for long-term impact of the movement of Metro trains, given that the buildings in the area are structures without piles, and so, not designed to take differential settlement. The JU report makes it clear that the structures in the first two categories are unsafe for people to live in. The third category includes houses that can be repaired and lived in. The fourth category consists of buildings that are safe and can be used after minor repairs. “The condition of the first two categories are the most worrying. Because of the vibration caused by Metro movements, the second category may easily move up to the first category. We may have to go back to the buildings two years after the Metro run to see how they have endured the vibration,” said a source.
KMC’s buildings department officials are concerned about the 40mm soil subsidence around a 10m radius beyond the site, where the shaft has been built to retrieve tunnel boring machines. “Though the experts are yet to recommend complete demolition of any building, they have painted a scary picture of some of the structures. These have been damaged beyond repair,” a senior civic official said. “KMC’s DG (buildings) will interact with KMRC officials and JU experts to reach a consensus on the demolition of unsafe structures,” mayor Firhad Hakim said on Tuesday.
