The partial collapse of the Champlain South Towers condominium in Surfside, Florida, is a reminder of how vulnerable structures near the coast can be. The 40-year-old, oceanfront apartment block was in need of substantial repairs, according to a report by an engineering firm, Thomas E Henz, in October 2018. Among the findings were lack of adequate waterproofing along the entrance driveway and pool deck, and “abundant cracking and spalling of varying degrees in the concrete columns, beams and walls” in the parking lot of the 12-storey building.
The “marine urban sprawl” as Emma Johnston, Dean of Science, University of New South Wales, calls it, plays a major role in rising water levels and land subsidence because of excessive groundwater extraction.
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While the causes behind the “pancake collapse” are yet to be established, construction close to the sea has to take several factors into consideration. In India, any construction along the coast has four fundamental checkpoints, building experts say.
Along coastal areas, there are sandy strata of considerable depth, and beneath this layer is hard rock or, sometimes, marine clay. “Usually, buildings are done on a pile foundation in these areas. Concrete piles are driven to rest on a suitable stratum deep into the ground taking into consideration the effect of any compressive layer underneath,” said structural engineer Santosh K, Principal Consultant, Design Spectrum, Calicut.
“The life of these underground members can be increased by carefully choosing materials that withstand the hostile saline environment. These could include chemical additives which improve the performance of concrete or sulphate-resistant cement,” said Santosh, who has been constructing high-rise buildings along the coast for two decades.
For the hard strata to support the foundation, engineers increase the area of concrete and make sure that steel is non-corrosive. “The concrete is made dense to help it become watertight,” said Santosh. “Ideally, if you have a reasonably good soil foundation… the piles are driven to a suitable depth and connected on top with a stiff beam-slab system, which will transfer the load to the soil.”
In buildings close to the sea, a major concern can be spalling, or saltwater seeping into concrete, causing support beams to rust and weaken over time, and leading to collapse. Corrosion too is common in coastal buildings, and erosion can happen depending on the cover of steel. Another concern in such areas is carbonation, causing the cement slurry around the structure to lose its protective ability. Once this chemical reaction reaches the reinforcement, corrosion increases rapidly.
These are a good way to maintain buildings close to large water bodies. In 2019, the Brihanmumbai Municipal Corporation (BMC) had stressed the need for structural audits on buildings 30 years and older. While the parameters vary for residential, commercial and industrial buildings, the basic checks included columns, beams, pillars, iron bars and plaster, sewage discharge systems, and water pipelines. A non-destructive test is usually recommended by the BMC’s empanelled structural engineer. While implementation remains a challenge, such timely interventions have helped prevent sudden building collapses.
“Besides global warming, the sea has its inherent way of getting back. When you start reclaiming the sea, and you encroach into its territory, the sea will take it back elsewhere. We have seen it across the world, be it in Mumbai, along the Kerala coast, Maldives or Dubai, water levels have risen… We have to do research to know more,” Santosh said.
In a June 26 report in The Washington Post, Surfside Commissioner Eliana R Salzhauer said about the collapse: “I think this is all tied to sea-level rise and our overdevelopment… Mother Earth comes back, and the ocean comes back, and takes it.”