Buildings
Construction May Play Role in South Florida High-rise Subsidence, Study Finds
Most of the coastal high-rises showing subsidence were located in Sunny Isles Beach.
Photo cropped from the original by Jimmy Baikovicius/CC BY-SA 2.0
Researchers found 35 high-rises along the coasts of Miami-area barrier islands slowly sank by as much as 3 in. between 2016 and 2023. While some settling during and in the months following construction is normal, the researchers say the subsidence continued for years and has shown no signs of stopping, though there are signs construction activity could be a contributing factor on both the structures being built and existing buildings located nearby.
The researchers from the University of Miami, University of Houston and other institutions published their findings in December in the journal Earth and Space Science. They looked at 87 high-rise structures in Sunny Isles Beach, Bal Harbor and Surfside, Fla., including 19 which were completed since 2014. Of those, 33 showed signs of subsidence, including 16 of the buildings from 2014 or later. Further south in Miami Beach, they found only minor subsidence at two out of 110 coastal high-rises.
Average heights of studied buildings range from 50 m in Surfside to 195 m in southern Sunny Isles. Buildings that subsided sank between 2 and 8 cm, according to the paper. In some cases, the rate of subsidence remained about the same, while in others it slowed over time.
“The discovery of the extent of subsidence hotspots along the South Florida coastline was unexpected,” said Farzaneh Aziz Zanjani, the study’s lead author, in a statement. “The study underscores the need for ongoing monitoring and a deeper understanding of the long-term implications for these structures.”
Because of the subsidence in those newer buildings, and other buildings located within 200-300 m of them, the researchers believe vibrations from construction may play a role. The area sits on porous limestone with sandy layers interbedded within, and researchers suggest vibrations from work may cause the sand layers to become more densely packed, and creep could continue under the sustained load due to fluidization. They added that pumping to draw down the water table for foundation work could result in similar effects, and also considered whether tidal flows could play a role.
The team’s analysis included Champlain Towers South in Surfside, the condominium building that collapsed in 2021, killing 98 people. The researchers say they detected no displacement before the collapse, even during construction nearby, indicating settlement was likely not the cause, though they note that their measurement points were not for the section of the building where the collapse started.
To measure the subsidence, the researchers used Interferometric Synthetic Aperture Radar (InSAR) from the European Sentinel-1 satellites. The remote sensing equipment can detect changes of just a few millimeters on Earth’s surface by comparing differences in radar signals over time. Other researchers validated the findings using data from the German TerraSAR-X satellite.
Antonio Nanni, a professor of civil and architectural engineering at the University of Miami, said in a statement that residents and officials should be informed about any subsidence of their buildings.
“Establishing a public database, similar to those in Europe, would enable residents, housing associations and authorities to monitor their buildings for signs of subsidence, inspect for cracks and take proactive measures,” Nanni said.
