SF's Millennium Tower Settles Another 1/10th of an Inch During One Week of Digging
Monitoring data shows the building settled 1/10th of an inch in the week that ended April 4. The building rebounded slightly at the northwest corner the following week, but experts worry the settlement at the corner will likely accelerate as more supportive earth is removed at the base. That earth, they say, has acted as a buttress alongside of the existing concrete slab foundation as the building continues to lean.
“So, as they take all that away, they’re losing lateral support,” said veteran geotechnical engineer Larry Karp. Karp first warned city building officials about the risks of the foundation retrofit back in 2019, before work started. He said then that the fix would inevitably cause the loss of supportive ground as piles were installed on two sides of the building.
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“This is uncharted and unpredictable territory,” said another veteran local geotechnical engineer, Bob Pyke, who had separately sounded the alarm about the risks of the fix before work began last year. Pyke said the new digging comes at a critical time, with the tower already pressing on the soil along Fremont Street from the stresses caused by installation of the piles.
“This is like having the man who is leaning forward and you excavate under the toes of his shoes,” he said. “That would be a dangerous thing to do.”
The engineer who designed the fix, Ron Hamburger, has told city officials to expect some additional sinking before the work is completed this fall. But Hamburger maintains the sinking would have occurred had there been no fix work on the building.
https://www.nbcbayarea.com/investigations/sfs-millennium-tower-settles-another-1-10th-of-an-inch-during-one-week-of-digging/2870828/
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