Work on the $ 100 million repair of the Millennium Tower has halted as engineers scramble to discover why the building suddenly plummeted an inch in just a few weeks since construction began, the NBC Bay Area investigative unit has learned.
The “Rundumpfahl-Upgrade” project – paid for as part of a settlement to a massive legal dispute over the listed concrete high-rise – is intended to support the foundation along the Missions and Fremont streets to prevent further settlement on the northwest corner.
After years of planning, in May the crews began drilling the first dozen of the three-foot-wide holes – each lined with steel sleeves – at a depth of about 30 meters. According to the plan, the crews would next sink up to 52 two-foot wide concrete piles through these steel sleeves an additional 30 feet into the bedrock.
A new bedrock-supported foundation shelf would then be attached to the old submerged foundation, which was a 10-foot concrete mat supported by 950 piles not attached to the rock.
There are more problems with San Francisco’s upscale and troubled Millennium Tower. The construction project to stabilize the sinking and crooked skyscraper was suddenly stopped this week. Investigative reporter Jaxon Van Derbeken, who followed the saga from the beginning, has more.
When foundation work began in May, the tower was sloped a little more than 17 inches at the top – with a subsidence rate that, according to engineers, seemed to have slowed over time.
But shortly after drilling began to drill the first dozen of the 36-inch-wide tubing for the piles along Fremont St., monitoring data received from the NBC Bay Area Investigative Unit in June showed apparent acceleration in both Sinking of the tower as well as when tilting to the west.
As of mid-August, data shows the foundation has sunk a full inch deeper since work began, resulting in a slope of up to five inches more at the top, resulting in a 22-inch slope towards Fremont and Mission .
In light of the latest data, the Millennium Tower Association informed local residents late Monday that further pile installation would be put on hold amid “an increased subsidence rate” as a total of 39 piles are pinned as part of the 52 piles.
The association informed residents that the planning team had decided to stop further stake installation on Mission Street out of “an excess of caution” as this “serves to better understand the cause and how to deal with it”.
“The building has not suffered any material damage,” the association assured residents, “and it will remain absolutely safe.”
The designers billed the fix not only as a stabilization of the tower but also as a partial straightening over time. The association says engineers in the meantime are looking for ways to mitigate the new settlement before work resumes. Doug Elmets, spokesman for the association, had no further comment on Tuesday beyond the letter to local residents on Monday.
David Williams, an Oakland-based structural engineer who specializes in foundations and bridges, said the latest dip and dip data was “worrying.”
“The trend is very worrying, the fact that they have reactivated the settlements,” he said, adding that the problem emerged so briefly after the crews had drilled only halfway to the bedrock.
“It is very risky to play around with something as complex as the foundation of this structure and not understand what is happening.”
Describing the project’s temporary halt, he added that if not stopped, the settlement threatens to inflict “undue damage” on the structure over time.