Work on the $ 100 million Millennium Tower repair has come to a halt as engineers scramble to figure out why the building suddenly sank an inch in a matter of weeks since construction began, the unit has learned. NBC Bay Area survey.
The “Perimeter Pile Upgrade” project – paid for as part of a settlement of a high-profile concrete skyscraper construction dispute – is designed to strengthen the foundations along Mission Streets and Fremont, in order to prevent a new settlement in the northwest corner.
After years of planning, crews in May began drilling the first dozen three-foot-wide holes – each lined with steel sleeves – about 100 feet. According to the plan, crews would then pour up to 52 two-foot-wide concrete piles through these steel sleeves for an additional 100 feet to bedrock.
A new foundation shelf supported by bedrock would then be attached to the sinking old one, which consisted of a 10 foot thick concrete mat supported by 950 piles that are not bound to bedrock.
There are more issues with San Francisco’s upscale and troubled Millennium Tower. The construction project to stabilize the sinking and tilting skyscraper suddenly came to a halt this week. Investigative journalist Jaxon Van Derbeken, who has followed the saga from the start, has more.
When foundation repairs began in May, the tower was tilting just over 17 inches at the top – with a sinking rate according to engineers that appears to have slowed over time.
But soon after drilling began to set up the first dozen 36-inch-wide casings for piles along Fremont Street, monitoring data obtained by the NBC Bay Area survey unit at from June onwards reflected the apparent acceleration of the tower sinking and tilting to the west. .
In mid-August, data shows that the foundation has sunk an inch since construction began, resulting in an additional five-inch tilt at the top, resulting in a 22-inch tilt towards Fremont and Mission.
In light of the latest data, the Millennium Tower Association told residents on Monday evening that further pile installation was on hold in light of an “increased settlement rate” as a total of 39 piles had been installed. under the 52- correction of piles.
The association told residents that the design team decided to stop installing piles on Mission Street out of “being cautious” because they “are working to better understand” the cause and how to deal with it.
“There has been no material damage to the building,” the association assured residents, “and it remains completely safe.”
The designers billed for the patch not only as stabilizing the tower, but also partially straightening it over time. The association says that in the meantime, engineers are looking for ways to mitigate the new regulations before work resumes. Doug Elmets, spokesperson for the association, made no further comments on Tuesday beyond Monday’s letter to residents.
David Williams, an Oakland-based structural engineering expert specializing in deep foundations and bridges, called the latest sag and slope data “disturbing.”
“The trend is the thing that is very worrying, the fact that they have reactivated colonization,” he said, adding that his concern is that the problem arose so soon after the teams had only drilled. ‘halfway up the bedrock.
“It’s very risky to play with something as complex as the foundation of this structure and not understand what’s going on.”
He called the temporary shutdown of the project “obvious,” adding that if not stopped, the regulation threatens to inflict “excessive damage” to the structure over time.