An outside expert is now advising the City of San Francisco and the Millennium Tower homeowners association about how to proceed with proposed testing on the troubled fix of the sinking and leaning high rise.
While the proposal is on hold for now, Millennium officials are hoping to start installation on a test pile as soon as next week. The testing is designed to help determine what has caused the additional sudden sinking and tilting since work started in May on the fix.
However, fix designer Ron Hamburger has predicted the drilling needed for the test pile could cause the building’s leaning to get worse.
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Patrick Hannan, spokesman for the Department of Building Inspection, said the drilling expert, Dan Brown, was hired last week to evaluate the testing plan. “He’s been providing feedback and insight on the planned proposal going forward,” Hannan said.
“The good news is that this is on hold until we get a third set of eyes,” said city Supervisor Aaron Peskin in an interview after meeting with the fix designer, representatives of the building and the city-appointed engineering review panel on the status of the $100 million project.
It was Peskin who had called for an outside review soon after NBC Bay Area’s Investigative Unit broke the news in August that the building had experienced accelerated sinking and tilting since fix work began in May.
At the time work began to install piles to support the structure to bedrock on two sides, the high rise was leaning 17 inches west toward Fremont Street. But after crews dug 33 holes to install support piles, the tower tilted additional 5.5 inches. That prompted all work to shut down in August.
At that point, the building was leaning 22.5 inches west toward Fremont Street. Just last month, the building sank again when crews bored new test holes at the corner where the structure is tilting the most. That testing work alone, data shows, led to another quarter of an inch of lean to the west.
Fix designer Ron Hamburger is now proposing to sink the new test pile to bedrock on the Fremont side of the building. But in a letter to city officials last week, he conceded that the new pile could trigger up to three quarters of an inch of added lean to the west.
Hamburger also specified 29 inches as the outer limit for the building to tilt for the tower to remain “safe and stable” in a major earthquake, leaving about six inches of more tilt to spare on the west side of the structure.
An inch of settlement at the base, data shows, translates into four to five inches of added leaning atop the 58-story tower.
“The ultimate question here is whether the cure is worse than the disease,” Supervisor Peskin said. “Not to use a cliché term, but if you are going to bomb the village to save it, that might turn out to be a terrible idea.”