One earthquake can put the leaning Millennium Tower in danger

Real Estate

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By Mary K. Jacob

June 13, 2023 | 5:50pm

The Millennium Tower, cheekily known as the leaning tower of San Francisco, is in trouble if just one earthquake hits the city, The Post has learned.

Located at 301 Mission St., the building, which stands 545 feet tall, has only continued to tilt further and sink deeper west since 2015, in spite of architects’ best efforts to steady the ritzy building.

The multimillion-dollar-per-unit tower is leaning more than 29 inches at the corner of Fremont and Mission streets — a slant more than half an inch deeper than previously revealed.

Consulting engineer Robert Pyke, who specializes in geotechnical and earthquake engineering, blamed the designer Treadwell & Rollo — a firm that was later acquired by Langan — for the foundation issues, citing a time crunch they were under during the 2008 market crash.

“There’s a real possibility that after an earthquake, the building might be red tagged,” Pyke told The Post of the tower — a 58-story, 419-unit residence that was completed in 2009.

When a building is red tagged it means the structure has been labeled severely damaged to the degree that is too dangerous to inhabit and prohibits entry to the property without written authorization by code enforcement.

Pyke cites the Hayward Fault Zone — a geological zone situated mainly along the western base of the hills on the east side of San Francisco Bay — as capable of generating destructive earthquakes.

“A quake on the Hayward Fault in the East Bay could occur any day,” Pyke said. “And even that Hayward … quake might be large enough to cause some significant rocking of the tool of buildings in San Francisco, like the Millennium Tower. So I think that’s the longer-term risk for the homeowners actually having to at least temporarily move out.”

Additionally, Pyke explained that the tower will never come back to level.

And while a collapse is unlikely, because it would need to tilt “tens of feet” for that to happen, Pyke said, if the tower edges closer to 40 inches, the elevators and the plumbing will stop working, and the residents will also be forced to move out.

The current fix has not worked and will likely not work because of their switch from steel to concrete in their original 2005 build — which makes it heavier and harder to change, Pyke said.

“It turned out not to be okay because the increase in the building weight effective was quite substantial. It was a third or more higher than it had been. And so the technical thing that it did was over stress the Old Bay Clay layer that was below the sand layer.”

Pyke said in order to prevent any more tilting, he would abandon their current fix attempt, which he says “has too many uncertainties.”

Instead he would drill borings (a cutting process that involves the use of a single-point cutting tool or boring head to enlarge an existing hole in a workpiece) on the south and east side of the tower to remove some of the soil in the Old Bay Clay layer in order to level up the building.

“Carefully!” Pyke said.

“This is similar to what was done on the leaning Tower of Pisa. Likely continuing settlement would then cease or slow down so much that it didn’t matter, but if it continued I might look at freezing the Old Bay Clay!”

Meanwhile, project engineer Ron Hamburger, responsible for the building, told NBC in a statement that rooftop figures are prone to weather fluctuations and said purely foundation-based data are more reliable.

“We are fully confident that following transfer of the remaining design load to the piles,’’ Hamburger said, “there will be no further … movement of the roof to the west.”