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Tilting Tower Developer May Drill Deeper

Tuesday, October 25, 2016

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The developer behind San Francisco’s famously sinking Millennium Tower has reportedly changed plans for another tower project in the same area, likely redesigning its foundation so that it’s drilled into bedrock.

According to the San Francisco Chronicle, Millennium Partners confirmed Thursday (Oct. 20) that it is bringing in structural engineers to the site of its new high-rise at 706 Mission St., just blocks from the Millennium Tower, to analyze soil conditions “at very low below-grade depths—up to about 300 feet below the surface.” That is much deeper than the new building's foundation was orignally planned to reach.

706 Mission rendering
Rendering: Handel Architects

Millennium Partners has already broken ground on the 706 Mission St. property, planned as a 45-story mixed-use tower, and home of the Mexican Museum.

The move comes about 10 weeks after reports surfaced that the 58-story Millennium Tower was sinking and tilting, to a degree not anticipated by the developers and builders. While some have argued that the issues with the tower stem from its piles not being drilled down into bedrock, the developer has held all along that the building needn’t be anchored down that far.

Millennium Problems

The tower, according to a report published in August, has sunk 16 inches since opening in 2008, and tilts about 2 inches to the northwest. Originally, it was expected to settle about 5 inches over time.

Millennium Partners has largely blamed the Transbay Joint Powers Authority for disturbing the tower while building its Transbay Transit Center on an adjacent lot. The TJPA countered that if the Tower had built on piles drilled down to the bedrock—about 200 feet down—it would not be tilting.

Millennium tower
By Daniel Ramirez – CC-BY 2.0, via Flickr

Millennium Tower in San Francisco has sunk 16 inches since opening in 2008, and tilts about 2 inches to the northwest.

The Millennium Tower is built on a concrete slab, with 14-inch square precast piles that extend 60 to 80 feet down. The tower is built on fill, as it rests beyond where the shoreline of the San Francisco Bay originally was.

While the settling is unsettling, not everyone believes it poses an immediate risk for the building. An earthquake-safe design expert hired by the developer issued a report earlier this month saying that the building was safe to occupy, even in the event of an earthquake.

Solid Ground

Millennium Partners has already broken ground on the 706 Mission St. property, planned as a 45-story mixed-use tower, and home of the Mexican Museum. It was designed by Handel Architects, the firm behind the Millennium Tower.

The new building at 706 Mission lies on more solid ground, but according to the Chronicle, the developer may err on the side of caution and drill down further anyway, if only to assuage the fears of possible tenants.

“I think you will find everybody in the marketplace has been alert to what has been on the front page for the last several months,” one developer told the newspaper, referring to the Millennium controversy and lawsuits that have followed.

Attempts to calm new buyers at the 706 Mission tower could lead to even more concerns elsewhere, though. One member of San Francisco’s Board of Supervisors told the Chronicle that the move should be a sign to the city to take a long look at any such building that isn’t anchored to bedrock.

“This turnaround proves that developers can afford to put in state-of-the-art foundation systems rather than cutting corners and skimping, and still have a viable project,” Aaron Peskin told the newspaper. “And it should be a sign to City Hall and our building officials that we should be insisting on the safest foundation systems available.”

   

Tagged categories: Architects; Architecture; concrete; Condominiums/High-Rise Residential; Engineers

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