Tilting Millennium Tower To Now Tilt Less, Engineer Says, With Piles Hitting Bedrock

1 month ago SFist

The long saga of SF's sinking and leaning Millennium Tower may soon come to a happy end, with the building still mostly upright and residents able to feel more secure.

Part of the planned fix for the Millennium Tower's well known tilt-and-sink problem, involving six support piles that extend from the building's foundation down to bedrock on the Mission Street side of the tower, is now complete. And as NBC Bay Area reports, via an update to tower residents from lead engineer Ron Hamburger, this should significantly stop, or maybe fully stop, the sinking that had been accelerated by the initial retrofit process with the piles.

"The purpose of this first stage of loading is to stabilize the building during the remaining construction, including the excavation along Fremont street to tie in the 12 piles already installed last year to bedrock," Hamburger writes in his email to residents, per NBC.

An earlier proposed fix with 52 total piles. There will now be only 18 piles. Rendering by Simpson Gumpertz & Heger

The building now leans 29 inches to the northwest, in the direction of the Mission/Fremont corner, and the next phase of the fix on the Fremont frontage is now beginning. NBC Bay Area notes that about a third of that tilt, around 10 inches, has happened since 2021 when the initial fix got underway.

It was six and a half years ago, in August 2016, when this tale of engineering woe began, after residents had been complaining of units not being level and an independent consultant concluded the building had tilted two inches to the northwest since it was constructed. Subsequent revelations would reveal that the building had sunk into the Bay mud beneath it, under its own considerable weight, in part because of a decision not to drill piles all the way to bedrock.

Being one of the first buildings of its height in the neighborhood, that was the engineers' prerogative at the time — and it was code-compliant at the city level. A subsequent legal fight occurred about whether the process to build the Transbay Transit Center next door, in which a significant amount of water was drained out of the ground, contributed to the sinking.

Most stages of the process to address the tilting and sinking of the tower have been well publicized, and the building continued to unevenly "settle" or sink more in the intervening years. Building residents also received payouts in a 2019 legal settlement with the developer and the Transbay Joint Powers Authority — and the Chronicle reported last year that unit sales don't seem to have been too deeply impacted, though it's probably impossible to conclude whether values have been depressed.

After work began in mid-2021 on the $100 million fix to shore up the building's foundation, engineers halted the project after a few months after the building sank an additional inch and was tilting an extra five inches on that northwest corner, just since the construction and excavation work began. At that point, the building had sunk 18 inches since its 2009/2010 construction.

While the fix, once complete, won't immediately solve the building's significant tilt, it will stop it from sinking further — and the hope is that the other corner of the building will eventually settle and even things out a bit.

This explainer video from 2021 does a good job of describing how and why the building the was constructed the way it was, and how the fix will work. And, the tower is being looked at now as a case study of geotechnical engineering that will likely be studied in schools for years to come — because, as YouTuber Grady Hillhouse explains, "Our ability to predict how soils will behave under new and extreme conditions isn't perfect, especially when those soils are far below the surface."

At least one engineering expert consulted by NBC Bay Area, Harry Poulos, remains skeptical that the building's issues will ever be fully solved, and he says, "I don't think there's any cause for optimism here."

Previously: Old Bay Clay and Foundation Piles: Millennium Tower's Tilting Troubles and Fixes Finally Well Explained

Photo: Justin Sullivan/Getty Images

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