‘Foundation failure of bldg on water body led to tilting’
Times of India | 15 January 2025
123 Kolkata: Construction of the building without a strong foundation on a plot that was reclaimed after filling up a pond was responsible for its tilt. "The building collapsed due to foundation and soil failure," civic engineers and structural experts told TOI on Tuesday.
"The building in south Kolkata's Vidyasagar Colony near Baghajatin was constructed around 12-13 years ago on a plot of land where a pond used to be. The soil was therefore soft and did not compact enough when the construction started. To build on such soil, the foundation has to be strong. That can be done by carrying out sheet piling and going deep. This was not done properly as deep piling leads to cost escalation. When the building came up, the foundation began to gradually settle, and this caused a tilt in the building," said a civic engineer.
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The developer, who retained a flat in the property that had eight apartments, attempted to rectify the tilt by using underpinning, a process in which the building is raised using hydraulic jacks to allow the foundation to be strengthened.
"The process of underpinning is applied by extending a foundation in breadth or depth such that its weight is distributed across a wider area or it sits on a more stable soil stratum. Jet grouting and micro-piles are some of the most commonly used underpinning methods. But in this case, the soil wasn't strengthened enough and collapsed, leading to the first-floor beam getting broken," said structural engineer Himadri Guha.
While this repair needs to be carried out under supervision of a structural engineer, KMC buildings department officials suspect workers were carrying out the job unsupervised. Thus, signs of distress went unnoticed.
According to the initial probe, the agreement with the firm stated that the tilt correction would be completed in a month and the foundation strengthening would take another 30 days. Work on the structure began five days ago.