Retrofit Proposed for Sinking Millennium Tower
The saga of the sinking Millennium Tower continues, but a fix may be in sight: drilling holes down to bedrock in order to stabilize one side of the tower while letting the other side sink down, allowing the building to level itself out.
With the work estimated to cost anywhere from $200 million to $500 million, this work could easily equal the original cost of the construction of the tower—$350 million.
Fixing the Sinking Tower
The structure’s sinking and settling led to gaps forming in the walls, which kicked off an investigation in 2016, after several residents had complained of “unexplained odors permeating their luxury units.”
In January, an exploratory drilling project evaluated the feasibility of the micro pile fix, which took 10 weeks.
According to the San Francisco Chronicle, the 58-story tower sits on a 10-foot-thick mat foundation, held in position by 950 reinforced concrete piles sunk 60 to 90 feet into clay and mud, which do not reach the bedrock. To fix the leaning issue, engineers are suggesting boring 275 to 300 steel and concrete “micro piles” down to bedrock, only on one side of the building at a time, starting with the west side.
Once the structure is stabilized, the east side would be allowed to sink until the building straightens itself. Then, micro piles would also be driven into that side, preventing the structure from sinking any further.
Repairs are slated to take two to five years. Currently, the building’s contractor and engineers are seeking the needed permits to complete the work.
But others are not so sure of the idea: attorney Frank Pitre, representing 85 Millennium condo owners separate the homeowners’ association, said that he thought this was not a fix. “At best, this is going to arrest further tilting of the building.”
David Casselman, a Los Angeles lawyer representing 265 owners separately from Pitre, is suing the Transbay Joint Powers Authority, which is currently wrapping up construction on the nearby Transbay Transit Center. Casselman claims that he has evidence that the authority—composed of the California High Speed Rail Authority, San Francisco, AC Transit, the Peninsula Corridor Joint Powers Board and Caltrans—ignored its obligation to prevent the structure from sinking when excavation work began on the Transit Center.
Test samples of the soil and bedrock will be taken in the next several days. Before repairs can begin, however, parties must come up with a comprehensive agreement to both fund the work and settle the claims from condo owners.
To date, the tower has sunk 17 inches and tilted 14 inches to the west and 6 inches to the north.