58-Story Luxury High-Rise in San Francisco Sinking, Tilting About 3 Inches a Year

The 58-story Millennium Tower luxury apartment building in San Francisco has continued to sink and is tilting about three inches per year, continuing to tilt even as construction was underway to stop it from doing so.

Last week, an NBC Bay Area report found that there was an average gap of one to four days between the removal of soil and the installation of concrete grout, which experts said may have contributed to the increased rate of tilting during construction.

Ron Hamburger, the fix engineer overseeing the project, said in a hearing in front of the San Francisco Board of Supervisors last week that changing to a new plan to install 18 steel piles in bedrock below the foundation of the building was preferable to the previous plan of 52 piles.

"The procedures for installing piles were basically the contractor's prerogative," Hamburger told city supervisors, according to NBC Bay Area. "We did not tell them how to install piles. We specified that we needed piles of a given diameter and strength. And he basically did those as a design build to install the piles in which he determined the methods by which he would install them."

Of the about 26 inches the building is currently tilting to the northwest, 10 inches reportedly happened while the building was undergoing the work over the last year, according to NBC Bay Area.

Hamburger said based on the current rates, it would be beneficial to minimize the amount that the construction can affect the building's sinking and tilting rates, and that the 18 steel piles would be the best way to stop it from sinking or tilting further.

He also said that within a few years under the current rate, the building could reach its theoretical limit of 40 inches of tilt, which would likely be the point that elevators and plumbing stop working properly.

Millennium Tower San Francisco Tilting Sinking
A view of the Millennium Tower on Aug. 11, 2016 in San Francisco, California. The engineer in charge of fixing the building reported last week that it was sinking and tilting at a rate of about three inches per year since construction started to fix it. Justin Sullivan/Getty Images

"The building does continue to settle at a rate of about one-half inch per year and to tilt at a rate of about three inches per year," he told supervisors last week. "It is doing this whether we are conducting work at the site or not."

Millennium Tower opened to fanfare in 2009 and all 419 apartments quickly sold out. High-profile residents have included former San Francisco 49er Joe Montana, late venture capitalist Tom Perkins and former San Francisco Giants outfielder Hunter Pence.

But by 2016, the building had sunk 16 inches (40 centimeters) into the soft soil and landfill of San Francisco's dense financial district. It was also leaning, creating a 2-inch (5-cm) tilt at the base and a 6-inch (15-cm) lean at the top. Residents sued the developer and designers.

The Associated Press contributed to this report.