A consultant working for the Millennium Tower developer on Tuesday formally submitted his proposed $100 million fix for the tilting and sinking Millennium Tower, a solution that involves floating one corner of the building off a new foundation that will be supported to bedrock.
“We are quite positive it will work,” said San Francisco structural engineer Ron Hamburger about his plan to halt and then partly reverse over time the tilting 58-story Millennium high-rise.
In his “perimeter pile upgrade” plan submitted to city officials on Tuesday, Hamburger seeks to drill 250 feet down into bedrock to install 52 piles to shore-up the building, now leaning 17 inches to the north and west.
“The piles will take the load down to rock, where it needs to go,” Hamburger said in briefing about his proposal. It involves installing 22 piles on Mission Street and 30 on Fremont. The two-foot thick circular steel piles would be filled with steel reinforced concrete.
The old 10-foot thick foundation mat would then be jacked up and bound to the new, slightly higher one installed under the sidewalk on the north and west sides. The work will take 18 months.
Meanwhile, as the rest of the tower continues to sink, Hamburger says the underpinned foundation will start to even out over 10 years.
“We expect that some of the tilt that has occurred to the building in the past,” Hamburger said, “will actually come out of the building and allow it to become plumb.”
It is still not clear who will foot the $100 million tab for the fix, but the Millennium Tower developer has agreed to oversee and warranty the work.
In a statement, Howard Dickstein, president of the Millennium Tower homeowners association governing board, said the board has “high confidence in the engineers who designed this retrofit, and we look forward to working with the city and county of San Francisco to get the project underway.”
The association recently rejected the $400 million solution that relied on piles sunk through the existing foundation.
Dickstein said that although city and other experts have consistently maintained the tilting building is safe, “this solution will eliminate any lingering questions about its stability and ensure future settlement is within the normal range."
Structural engineer Joe Maffei said he likes Hamburger’s approach over the earlier plan to sink new piles through the existing 10-foot thick foundation.
“This is an effective solution to stop the settlement in the corner where they are putting the piles,” he said, but warned it could also mean headaches for residents.
“There’s a lot of drilling," he said. “When they do that drilling, how much of that drilling sound transmits up into the occupied spaces, you know, is something they’ll have to determine.”
But before any drilling begins, the city-appointed independent peer review panel must sign off on the plan. The city administrator’s office issued a statement promising an expeditious review of the submission.
Meanwhile, as he waits, Hamburger says he understands what is at stake.
“I have been working on the project for four years and have done more extensive analyses on this building than any building I have ever designed or retrofitted before,” he said on Tuesday. “I want to get it right, and I believe that I will get it right.”