Source: https://www.constructiondive.com, April 20, 2018
By: Kim Slowey

Dive Brief:

• Engineers tasked with finding a way to stabilize the sinking Millennium Tower in San Francisco have suggested a fix that could cost between $250 million and $500 million dollars, according to the San Francisco Chronicle. The residential skyscraper cost $350 million to construct in 2008.
• Crews would drive 137 to 150 13-5/8″ steel and concrete “micro piles,” anchoring the west side of the building to the bedrock below. Engineers would allow the east side of the building to continue to sink until the tower straightens itself out. At that point, after two to five years, workers would install an equal number of piles on the east side, hopefully preventing the building from sinking farther. The building currently sits on 950 piles driven 60 to 90 feet into clay and mud.
• Already some residents have expressed concern about the possible effects such a process could have on the structure’s concrete pad and the building itself, which has already been stressed from sinking 17 inches and tilting 14 inches to the west and another six to the north. Crews will soon start soil testing at the Millennium, but residents, developer Millennium Partners, insurance companies and others are still trying to come to an agreement as to who will pay for the work.

Dive Insight:

Residents have complained that the tilting and sinking are affecting their property values, ability to obtain homeowner’s insurance and even the aesthetics of their units, but the real concern likely revolves around whether it is safe to continue to live in the Millennium as is.
In December, NBC Bay Area reported that potential “life and fire safety hazard” information was omitted from an assessment given to residents in December 2016 about the condition of the building. A consulting firm was hired to try to determine the source of bad odors throughout the building and what they ended up discovering was that the odors were emanating from gaps that had been created between the curtain wall and main structure, a result of the building’s settling. More troublesome than the odors, however, was the consultant’s finding that the spaces constituted a breach of the building’s fire and smoke barrier, which, if accurate, means that the residents’ safety is at risk.
City inspectors subsequently issued a fire safety risk violation citationagainst the Millennium, which means Millennium partners must either fix the problem or find a qualified party to vouch for the building’s safety.
As far as the risk of earthquake damage and safety, city engineers in a July 2017 report found that the Millennium could likely withstand an earthquakebut added that the building’s significant settlement issues warranted an “in-depth investigation.”