SAN FRANCISCO—The drilling of three holes around the Millennium Tower, located at 301 Mission Street, began on Monday, September 26, by soil experts that are representing Millennium Tower homeowners, according to reports. The testing of the soil comes after it was reported in August by The San Francisco Chronicle that the 58-story luxury high-rise has been sinking and tilting more than expected.
The soil tests will collect data on the water and soil conditions underneath the building. The tests will last 3 weeks with two holes being drilled on Mission Street along the front of the Millennium Tower and one hole being drilled around the corner on First Street.
“What they will tell you is where is the soil compressing, where is it settling,” said Patrick Shires, the geotechnical engineer overseeing the operation.
The workers will drill a six 6-inch wide hole using a rotary drill that will go 260 feet into the ground. Three instruments will be dropped into the hole, an inclinometer, a piezometer and an extensometer. These tools will measure the building’s tilt, the groundwater soil conditions, and how much soil is underneath the building going all the way to the bedrock.
These tests come as a result after reports were made in August of the Millennium Tower sinking and tilting. On Thursday, September 22 a 3-hour Board of Supervisors hearing was held to discuss why officials at the San Francisco Department of Building Inspection didn’t open an investigation into structural issues at the Millennium Tower until after The SF Chronicle reported building issues in August.
According to reports, there is evidence going back 6 years that the building had been sinking more than the four to six inches the project engineers had anticipated the building sinking in its lifetime. The Millennium Tower, located north of the Transbay Transit Center, has settled 16 inches and is tilting two inches to the northwest.
“There is no question but that the city and the developer knew as much as six years ago that the building was sinking much more than anticipated,” said Supervisor Aaron Peskin at a hearing of the Government Audit and Oversight Committee. “I am interested in knowing why the city did not disclose that to the public or to the over 400 individuals, families and entities that purchased units in the building.”
The Millennium Tower developer, Millennium Partners, claims the tilting and sinking are due to soil dewatering at the Transbay Transit Center. Millennium Partners say that the water table underneath the building has dropped 20 feet and has weakened the soil underneath the foundation. The developer for the Transbay Transit Center, Transbay Joint Powers Authority, claims that Millennium Partners had erred when they built the foundation with piles 66 to 91 feet instead of the 200 feet that would have reached the bedrock.