The ongoing project to shore up the foundation of the sinking and tilting Millennium Tower in downtown SF is temporarily on hold as engineers examine some newly accelerated sinking and tilting of the building.
The saga of the 58-story tower becoming the "Leaning Tower of San Francisco" dates back five years, to August 2016, when the first report arrived that the high-rise — home to the likes of Joe Montana and Hunter Pence — had sunk over sixteen inches in the eight years since construction began. One cause, as engineers quickly surmised, was the fact that the developers had failed to drill pilings down to bedrock for the foundation — something that the nearby Salesforce Tower has. But the developer pointed fingers back at the next-door Transbay Transit Center's construction, saying that "de-watering" of the soil for that project led to increased "settlement" for the Millennium Tower.
Fast-forward through a frenzy of local and national media coverage and a bunch of lawsuits, and a $100 million fix was landed upon in which new pilings would be drilled down to bedrock, and the existing foundation of Millennium Tower attached to those, to stop the sinking and, eventually, fix the tilt.
But as NBC Bay Area reports, residents were informed recently that the project has temporarily stopped out of "an abundance of caution" because the building appears to have sunk more rapidly than it had been in just a few months. Drilling for the new piles began in May, and in June, engineers reportedly found accelerated sinking and tilting, which now amounts to a full inch of sink since the work began. That translates to an extra five inches of tilt at the top, for a total of 22 inches in the direction of Fremont and Mission streets.
"There has been no material harm to the building, and it remains fully safe,” says the Millennium Tower Association in a letter to residents about the temporary construction pause.
Nervousness about the tower's ongoing troubles was heightened following the June collapse of Champlain Towers South in Surfside, Florida, which brought issues of structural integrity into the national spotlight. But Millennium Tower head engineer Ronald Hamburger told CNN in July that there shouldn't be cause for any comparisons.
"Millennium Tower was designed to stringent earthquake resistance standards and is a much tougher form of construction than typical buildings in Florida, which are not required to be designed for earthquake resistance," Hamburger said. "I can state with confidence that settlements experienced by Millennium Tower have not compromised its stability and safety."
But an outside expert, Oakland-based structural engineer David Williams, tells NBC Bay Area that the new data on accelerating sinking is not nothing.
"The trend is the thing that’s very disturbing, the fact that they have reactivated settlement,” he tells the station, adding that the speed of the new sinking is of special concern."
He also says, "It’s very risky playing around with something that’s as complex as this structure’s foundation and not understanding what’s happening," adding that "excessive damage" to the tower could result from more rapid sinking at this stage.
It remains to be seen when the foundation-shoring project will resume.
Photo by Justin Sullivan/Getty Images