The collapse of a residential building in Miami: soil subsidence under it was reported 30 years ago
The building, built in 2020, has plunged into the ground at an alarming rate since the 1981s, according to a 1990 study by Professor Shimon Wdowinski of the Department of Earth and Environment.
When Wdowinski saw the news of the demolition of the Champlain Towers South condominium in Surfside, he was immediately reminded of his research.
Wdowinsky said there was no data on what caused the destruction. The building sank at a rate of about 1990 millimeters per year in the 2s, he said, and could have slowed or accelerated since then.
In his experience, even the level of sinking seen in the 1990s usually has an impact on the building and its structures, Wdowinsky said. Judging by his findings, it is quite possible to apply to the collapsed house.
“We saw that there was some unusual movement in this building,” Wdowinski said.
Daniel Ditch, who served as mayor of Surfside from 2010 to 2020, warned against jumping too soon.
“This is an extremely unusual event, and speculating on its causes is dangerous and counterproductive,” he said.
Officials said 35 people were rescued and confirmed at least one death, although they said they expected an increase in the death toll. To date, 99 people are reported missing.
Surfside Town Commissioner Eliana Salzhauer said, “This was not a natural disaster. Buildings don't just fall down. "
Water damage and cracks
The county requires commercial and multi-family buildings to recertify every 40 years. The process includes electrical and structural checks.
Salzhauer said no serious complaints about the building have been brought to the attention of the authorities.
“If there were serious problems in the building, we would definitely know about it,” she stressed.
In 2015, a lawsuit alleged that the building's administration was unable to support the outer wall, resulting in water damage and cracks. Judging by the materials of the court, the person who filed the lawsuit had previously complained to the court on the same issue. According to the records, the management company paid for the damage in the previous case.
According to Matthis Levy, a consulting engineer, professor at Columbia University and author of Why Buildings Collapse: How Structures Collapse, there may be clues as to why cracked walls or shifting foundations indicate sinking is affecting structural stability.
According to him, the residents of the house could have noticed the changes.
“Perhaps there were changes in the building? Cracks in the walls, in the floor? Are the floors uneven, were things rolling off the tables? " - the expert specified. This indicated that the building was sinking.
The city needs to invest in technology that can determine which buildings are at risk of collapse due to geologic processes, said Keren Bolter, a Florida geologist with engineering firm Arcadis, which advised the FDA on hazard mitigation.
“I think we have a systemic problem,” she said. "Investing in prevention instead of reacting saves lives, money and time."
According to Ryan Chamette, a professor of engineering at the University of North Florida, satellites, drones and other means are used to understand which buildings may be in danger. He believes that these efforts differ depending on the jurisdiction and on whether the structures are privately or publicly owned. According to him, in addition to analysis during construction, monitoring is usually not carried out in advance.
“Structural monitoring already exists,” Shamet said. - But it is difficult, because we do not yet have the resources to control each structure. First you need to find out if there is a problem before you start tracking it. "
There is always concern about buildings being built on reclaimed land, Levy said.
The reclaimed land, be it a landfill or wetland, can become compacted over time, resulting in shifts in the ground below the building.
“A millimeter may seem like a small figure, but if you add up each of them over many years, you get a large number,” said Levy.
A building could be particularly vulnerable if the ground on which it was located dropped at different rates, causing uneven subsidence.
“The important thing is that one part of it is still standing. The collapsed part could sink faster than the other, ”explained Levy.
“Some kind of trigger has to go off. If you have two parts of a building, one with a solid foundation and not moving as much, and the other not, then you get movement between them. This can cause skewed floor slabs, which will begin to crack, ”he said.
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This leads to the so-called progressive destruction, when one part fails, then the second, the third - until the entire structure fails. This is exactly what happened to the World Trade Center after the September 11 attacks, he said.
“Buildings are not heavy-duty; they are not designed to withstand unusual events like this, ”he said.
“If one part of a building fails, the rest is gradually pulled in after it,” he said. "And there is nothing that can stop or restrain it."
Impact of sea level rise and flooding
Over the past few years, Wdowinsky and his team have investigated which parts of the Miami area are sinking, primarily to determine where sea level rise and flooding could have the greatest impact. They received historical data from satellites, which mapped the area by transmitting signals to and from the ground to determine altitude displacement.
The results were published in April 2020.
Data collected from 1993 to 1999 showed that much of the Miami area did not dip significantly, with the exception of a few hotspots. Most of them occurred in western Miami, where the altitude is lower, Wdowinski said. The drawdown rate at Champlain was unusual, he said.
Wdowinsky does not believe that anyone in the city or state government had any reason to know the results of the study. Much of this has focused on potential flood hazards rather than engineering concerns. The mention in the study of "12-storey condominium" was put in one line.
“We didn't attach much importance to this,” Wdowinsky said.
The incident prompted him to consider using such data to identify areas of potential structural risk, he said.
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