Update: San Francisco's Millennium Tower is now 26 inches off center, with 10 inches of that tilt occurring last year while work on a supposed fix was underway, according to the project's chief engineer. A retrofit was halted in the summer after the building sank further into soft soil, with engineers last month blaming soil removal and vibration as six steel support piles were installed in August, per NBC News. Structural engineer Ronald Hamburger told a city hearing Thursday that the best path forward would be to reduce the originally proposed 52 piles to 18. He added the residential tower continues to tilt at a rate of three inches to the north and west each year, per NBC Bay Area. The city said it would complete a review of his proposal by March. Our original story from August follows:
The $100 million project to stop the Millennium Tower from sinking into the San Francisco earth was going fine—until the building sank another inch. Now the construction work has been stopped, SFGate reports, and luxury condo residents who have worried about this since 2016 will continue to stress. Since the work began in May, the building has added to its lean; it's now tilting 5 inches toward Fremont Street, 25% more than before, per NBC Bay Area. The work was halted on Aug. 2, shortly after the project's lead designer offered reassurance in late July that a half-inch settlement was nothing to worry about. The steps involved in the fix were:
- Drill holes 3 feet across along Mission Street.
- Line the holes with tubular, steel shafts.
- Sink smaller piles inside the steel shafts to bedrock, 250 feet deep.
- Connect the new foundation, under the sidewalk, to the original one.
The problem might be the steel shafts. Ronald Hamburger endorsed stopping the drilling for the shafts to see if that was compressing the soil; the 1-inch drop happened once the first of the 52 piles had been installed. The foundation is built on sand instead of bedrock, but that's true for other San Francisco towers that aren't sinking. Hamburger said the work will stop for two to four weeks.
One structural engineer said it's clear this fix isn't going to work. "The way to solve the problem, as I see it, is not to continue going on the route that is showing you the wrong route, but to recoup, reconfigure the solution and do something that has a better chance of working," Joshua Kardon said. Hamburger stands by the plan, saying that once the piles are in place and the weight shifted to them, the tower will "begin to recover some of the tilting," he said. "There has been no material harm to the building and it remains fully safe." (Read more Millennium Tower stories.)