It’s been about 2 years since the public became aware that San Francisco’s Millennium Tower, a 58-story luxury condo high rise, was significantly sinking and tilting. Our last update on the tower was almost a year ago, when an engineering firm determined that the tower had continued to sink and tilt at a rate that was twice as fast as originally estimated. Now, engineers believe they have determined a way to keep the building from continuing to move, but it’s going to be an extremely lengthy process and be extremely costly.
The building is currently supported by a mat foundation that’s 10 feet thick and 950 reinforced concrete piles between 60 and 90 feet deep. Some have blamed the sinking on the nearby Transbay Joint Powers Authority (TJPA) project and others have blamed the developers for not driving the piles down to bedrock around 300 feet deep during the original build.
The stabilization proposed by engineers is pretty interesting, because it will only stabilize one side of the building first to allow the other side of the building to continue to sink until the building is level. Once the building is level, the other side will be stabilized. In order to stabilize, contractors will have to install a total of 275 to 300 “micro piles,” which are made of concrete and steel and measure 13 5/8 inches in diameter.
The original building cost developers around $350 million and estimates for the fix are currently ranging between $200 million and $500 million, potentially doubling the initial investment.
The project is also estimated to take between 2 to 5 years to complete, which has received mixed reviews from the building’s occupants, according to the Chronicle. Some, including one of the lawyers representing 265 of the homeowners, believes that the only true fix would be to tear down the building and start over.
According to the San Francisco Chronicle, the building’s general contractor and its engineers have already begun the building permit process and the gathering of other approvals in order to begin the fix. There are still plenty of legal battles set to play out, but equipment is already scheduled to be on-site to get boring samples of the soil down to the bedrock.
Full story: Pricey retrofit proposed for sinking Millennium Tower in SF | San Francisco Chronicle