The head of San Francisco’s Department of Building Inspection asked Millennium Tower officials Friday to hold off on doing more work on the so-called fix to the sinking problem until experts agree on ways to prevent more unexpected sinking and tilting of the structure.
Last weekend, the general manager of the building told residents they could expect work to resume on the fix “shortly,” assuring them that engineers had figured out how to drill holes to install support piles without further destabilizing the ground around the existing foundation.
Since work started in May to bolster the foundation on two sides, the tower has sunk more than 1.3 inches on the northwest side, data released Friday shows.
It’s currently leaning 22 inches toward Fremont Street. The “fix” engineers say holes crews have drilled into the ground to install new support piles to bedrock were “slightly” too large.
Experts say that in the process, soil would typically shift to fill the voids and away from the building’s foundation, causing that side to sink more into the less stable ground. In a letter to the general manager of the tower, also released Friday, DBI head Patrick O’Riordan asks tower officials to hold off resuming work to allow time to “continue to review and provide feedback” on “an updated construction approach to ensure that the building remains safe for the occupants and compliant with the San Francisco building code.”
“I think that’s an appropriate thing to do,” said veteran geotechnical engineer Dr. Robert Pyke, who predicted problems with the fix back in 2019, before it was approved by a city-appointed expert review panel.
Pyke says a freeze in restarting the project might help overcome the problem now, but there will no doubt be other challenges once work resumes.
“They should never have begun this attempt at a fix,’’ he said, “and the recent events have served to indicate that they don’t have a full understanding of what they are doing and it might well be time to terminate it.”
But O’Riordan said in his letter that at this point, the city’s review panel agrees with fix engineers that the recent additional sinking doesn’t raise a structural concern.
It is not clear, however, how long it will take for city officials and experts to agree on a way to safely sink all of the remaining steel support piles to bedrock without further destabilizing the tower’s foundation.
Source: NBC Bay Area