Foundation retrofit work was halted at Millennium Tower in San Francisco after it was found the project to prevent further sinking was in fact causing the building to sink faster than before.
The nearly US$ 100-million perimeter pile upgrade project began in November 2020. It involves installing 52 concrete piles that would anchor the building to bedrock, 76 meters (250 feet) below ground. The work was halted for a two- to four-week moratorium until it was understood what was causing the increased settlement rate.
Millennium Tower, completed in 2009, has been sinking since 2006, according to the Los Angeles Times. The building’s foundation reaches to a layer of sand above a layer of clay, instead of down to bedrock. This is common practice in San Francisco, but Millennium Tower is much taller and heavier than the typical building in the area. It is the 6th tallest building in San Francisco, and is a direct neighbor of Salesforce Tower, the tallest building in the city. As of 2018, the sinking has reached 45.7 centimeters (18 inches), with a lean of 35.6 centimeters (14 inches) toward the northwest, according to an article in the San Francisco Chronicle.
A spokesman for the building’s homeowners’ association said the building remains fully safe. In October, the association said that Millennium Tower’s tilting and sinking had virtually halted over the prior two years.
Millennium Tower was developed by New York-based Millennium Partners.
For more on this story, go to the Los Angeles Times.