Residents of Bandra and Andheri are on safer ground compared to those of buildings constructed on land reclaimed from the sea in areas such as Bhandup and Borivli.
That’s because buildings in Mumbai’s reclaimed areas are more likely to be damaged during an earthquake than those elsewhere, according to a study done by the Indian Institute of Technology-Bombay (IIT-B) and Veermata Jijabai Institute of Technology (VJTI), Matunga. During an earthquake, the soil in reclaimed areas could take on a liquid quality and flow like muddy water, affecting building foundations.
The study, published in the March issue of the Journal of Applied Geophysics, is important because the different ways in which soil reacts during tremors could necessitate area-specific construction designs in Mumbai.
“A building design suitable for Andheri may not be safe for Borivli,” said IIT-B Professor Deepankar Choudhury, one of the researchers. “When land is reclaimed, soil is dumped into the sea so the chances of liquefaction increase. You need to take special care while designing earthquake-resistant measures in such areas. However, this is not normally done.”
The study is important for Mumbai, which falls in the moderate Seismic Zone 3 and is susceptible to earthquakes measuring 6 to 6.5 on the Richter scale. There are 23 fault lines along Panvel, Thane and Dharamtar creeks around Mumbai. On July 1, moderate tremors measuring 3.1 on the Richter scale were felt in parts of Diva and Thane.
The research team prepared a soil liquefaction susceptibility map for Mumbai’s original seven islands. Soil liquefaction is a phenomenon in which cohesion-less soil — usually sandy or clay — flows like muddy water.
The map could help urban planners design more efficient quake-resistant buildings. “At present, soil testing is done to see how much load it can take. But there is no assessment of what will happen to the soil and or how the foundation will react during an earthquake. Knowing the intensity of soil liquefaction will help builders draw designs suited to the construction site,” said VJTI Professor Sumedh Mhaske. This would make buildings safer.
“Soil testing is done before constructing a building; we also consider the eventuality of a quake. A susceptibility map would be useful,” said Sunil Mantri, proprietor, Mantri Builders.