SAN FRANCISCO (KPIX 5) — Plans were submitted Tuesday for a project to fix the Millennium Tower in San Francisco, which is sinking and has currently tilted 14 inches.
The project aims to stop the tilting and even out the base by 50 percent in the next ten years.
The discovery in 2016 that the tower is sinking and tilting on the northwest side set off a flurry of lawsuits among dozens of parties, including the building’s owner, the developer and homeowners.
After lengthy, confidential negotiations, the Millennium Tower Homeowners Association, the owner, Mission Street Development, LLC and the developer, Millennium Partners, agreed on a strategy to fix the Tower, which is now leaning 14 inches to the northwest.
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Ronald Hamburger is a senior principal engineer at Simpson Gumpertz Heger and the one who came up with the idea.
“We developed a design we’re calling the ‘Perimeter Pile Upgrade,'” said Hamburger. He said the plan is to install 52 pile foundations along the north and west sides of the structure.
“They’ll be placed underneath the sidewalk and tied into the main building foundation,” he explained.
The current piles don’t go deep enough to sit on bedrock underneath the tower, so Hamburger’s team will install new, longer piles around the existing ones that will reach down all the way.
“We’ll take about twenty percent of the weight of the building off of the existing foundation and transfer it to the new piles, which will extend down into bedrock,” explained Hamburger.
Then, they’ll attach those longer piles to the foundation on the corner which is sinking. The process is called “underpinning” and Hamburger says its commonly used for smaller buildings.
“It’s not unusual to do this type of thing to a building. What is unusual about this is the size of the building–very large,” said Hamburger.
The underpinning process will prevent further sinking and raise the corner that has sunk about an inch, but it won’t even out the building right away,
The northwest corner will rise up about an inch and stay stable while the rest of the building continues the normal process of settling into the land.
“Over time, as the south and east sides settle a little bit more, we expect that about 50 percent of the tilt will come out over a period of ten years. More will come out over a longer duration, perhaps fifty years or so,” explained Hamburger.
On Tuesday, the plans for the project were submitted to the Department of Building Inspection, and Hamburger estimates that construction will commence in the spring.
“We estimate it’ll take about eighteen months to do the construction,” he said.
Until then, one lane of Mission Street and one lane of Fremont Street will remain closed.
While there is agreement among the main players that this new fix is the way to go, they have not yet decided who will pay the $100 million dollar price tag.