With the initial round of testing having proven successful, the plans to permanently stabilize the sinking Millennium Tower by adding a series of 52 new piles around the tower’s perimeter have been further refined, building permits for the fix have been requested, and a final round of pre-fix testing is about to get underway.
As envisioned, a 10-foot wide, 27-foot deep, trench would be excavated along the tower’s western perimeter fronting Fremont Street, and down 125 feet of Mission Street, allowing for the installation of the aforementioned new piles, each with a diameter of 24 inches, between the tower’s existing mat foundation and down to the bedrock below.
The retrofit would transfer around 20 percent of the tower’s weight to the new piles, “with intent of arresting [building] settlement and improving the foundation lateral capacity,” reducing stress on the tower’s mat foundation and Old Bay Clay below.
And while the stabilization project is currently expected to take around two years to complete, the perimeter approach will minimize the impact on the building’s residents and garage, neither of which will need to be vacated for the project to proceed.
But once again, exactly who is going to be on the hook for covering the cost of the fix could take nearly a decade to resolve, with the Transbay Joint Powers Authority (TJPA) named in nearly a dozen lawsuits related to the sinking tower at 301 Mission Street, which is adjacent to the TJPA’s new Transbay/Salesforce Transit Center project which is now being fixed as well.