Sinkhole didn't cause Miami's Champlain South collapse

Champlain Towers South: The sinkhole was the easy hypothesis

In the early hours, an apartment building in Surfside, north of Miami Beach, was split in two, leaving dozens dead and missing. The Champlain South tower, built in 1981 at 8777 Collins Avenue, collapsed in seconds while most residents slept. The local mayor, Charles W. Burkett, described the scene with a phrase that became a headline: "It's like a bomb went off, but we're pretty sure a bomb didn't go off, so it's something else."

At least 10 people were treated for injuries at the scene—one of them fatal—and 99 missing were counted in the first hours. The underlying question remains: what brings down a reinforced concrete building in a first-world country, without warning and without obvious cause. The answers circulating that week have little to do with those that ended up on the table.

What really peine in the Champlain South tower collapse?

The first hypotheses pointed to the ground. There was talk of soil liquefaction, beach sand in the concrete—salinity eats away at rebar—, a sinkhole 50 meters in diameter and 3 meters deep between the pool and the building, and leaks in pumping pipes. It was argued that Miami was sinking and that hundreds of towers from the 1960s, 1970s, and 1980s would have to be demolished or underpinned. The sinkhole, however, was ruled out.

Samples extracted from the slabs and columns that remained standing pointed in another direction: a textbook punching shear failure, that is, a column piercing through the slab it supported.

The Sarracena report and the ground floor full of holes

An engineering report submitted years earlier to the municipality of Surfside—known as the Sarracena report—already described the lower part of the building as a Swiss cheese that left rebar and reinforcement exposed. They tried to cover it up. It wasn't done properly. That document and the accompanying photographs became the most solid documentary trail of a structural problem that had been on the table for years and that no one wanted to pay for in time.

The core sample extracted next to the planter that collapsed first draws the error with workshop precision: a slab 15 centimeters (6 inches) with the reinforcement in the sixth inch, that is, 6.25 centimeters from the top surface. Neither at the top nor at the bottom. In the middle of the concrete, where it provides no support.

Why did the structure fail and not the foundation?

The analysis of the original plans led to a different conclusion from the ground: the origin could be in an unreinforced column, overloaded with the weight of a planter and cars parked in the area that did not collapse, after it was decided to eliminate some beams that were thought unnecessary after design changes. In flat slabs, shear reinforcement—punching shear—is the only thing preventing the column from piercing the slab.

The warning was written in black and white in the subsequent inspection: five of the six columns analyzed were damaged and the building was still standing.

Why did no one pay for the repair in time?

Repairs in a homeowners association are a mess as soon as the bill appears. If some of the apartments are second homes and their owners spend four weeks a year there, spending thousands of dollars on special assessments becomes a decision that can always be postponed. The perverse incentive is well known: those who don't live there don't see the problem, and those who do can't pay for it alone. Meanwhile, the building ages.

Is Miami sinking?

Florida is the flattest terrain in the country. Its highest mountain is around 117 meters, near Pensacola; in the south, the highest point is a landfill of about 45 meters. A 1923 aerial photo shows that where the tower now stands there was water: a canal connecting the sea with the bay. Add to that groundwater, which seeps in, creates caverns, and ends up moving whatever is above. Upward flows from the ground were considered an aggravating factor, never the sole cause.

The unproven theories surrounding the collapse

As in any catastrophe, some looked for a culprit before the experts arrived. The name of an offshore company registered in an apartment in the building and linked, according to social media posts, to the circle of a public figure circulated. There was also talk of controlled demolition and sabotage. None of that appears in any technical report.

The bill for greed

"Crime, delinquency, corruption and incompetence: how Champlain South Tower was built," headlined a report on the case. "Financed by greed, built by incompetence." The summary is harsh, but it fits what the core samples show.

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The uncomfortable question remains. If the failure was in the design and maintenance, and not in the geology, how many towers from the 1960s, 1970s, and 1980s are still standing with the same flat slab, the same sand in the concrete, and the same homeowners association willing to postpone the special assessment for another year?