Residents living within San Francisco’s Millennium Tower will submit a permit application to shore up the 58-story building that has been slowly sinking into the soils beneath it. The project would require drilling more than 50 new piles down to bedrock 250 feet below, costing nearly $100 million.
According to the San Francisco Chronicle, the soils that are heavily stressed along the north and west sides of the building have caused it to lean 14 inches west over the years.
Ronald Hamburger of the firm Simpson Gumpertz & Heger, designed the plan. He told the Chronicle:
The contractor would drill 22 new piles along Mission Street and 30 along Fremont Street. Each pile is 24 inches in diameter and weighs 140,000 pounds and would take three or four days to drill into place. A reinforced concrete “inner pile” would be installed within each steel shaft. That shift would relieve stress on soils that have compressed beneath the building, causing it to settle more than anticipated and to tilt.
The proposal is said to outline $30 million worth of work, but the entire upgrade would cost nearly $100 million, and take 18 months.
“We have high confidence in the engineers who designed this retrofit, and we look forward to working with the city and county of San Francisco to get the project under way,” said Howard Dickstein, president of the Millennium Tower Association’s Center board of directors, in the report.
The plan will be reviewed by a panel, and could begin construction in late winter or early spring. The work will be underground, and should not cause much disturbance to residents.
Source: The San Francisco Chronicle