Dec. 5 (UPI) -- Homeowners living in San Francisco's sinking and leaning Millennium Tower have presented a $100 million plan to fix the problem that's plagued the city's tallest residential tower for nearly a decade.
The 58-story skyscraper sits on a 10-foot-thick concrete mat foundation held in place by 950 reinforced concrete piles, which are driven deep into the ground. Since its opening in 2009, the building has sunk 18 inches, leans 14 inches to the west and 6 inches to the north -- leading residents to worry about its safety, particularly in an earthquake-prone city like San Francisco. It's become known as the city's Leaning Tower of Pisa.
The Millennium Tower Homeowner's Association and Mission Street Development agreed to a plan to retrofit the foundation with new concrete piles, hoping to stop the sinking and reverse the tilt. The plan, though, submitted Tuesday, needs approval from both the city and county of San Francisco.
"Today we submitted ... a permit application that outlines the plans for what we've called the 'Perimeter Pile Upgrade' to install 52 concrete piles that are going to transfer a portion of the building's weight from its existing foundation system to bedrock which is 250 feet below," homeowner's association spokesman Doug Elmets told UPI Tuesday.
If approved, contractors will install 22 new perimeter piles along Mission Street and 30 along Fremont Street, each measuring 24 inches in diameter and weighing 140,000 pounds. The engineers who designed the plan said the new reinforcement on the north and west sides of the tower will keep it from sinking too far and straighten the tilt.
"We have high confidence in the engineers," Howard Dickstein, president of the Millennium Tower Association's Center Board of Directors, said. "While the city and other experts have always certified the building as safe, this solution will eliminate any lingering questions about its stability and ensure future settlement is within the normal range."
The new plan outlines $30 million worth of work, but the entire upgrade adds $70 million to the price tag and would take 18 months to complete, The San Francisco Chronicle reported.
Each of the 52 concrete piles would take several days to drill into place. Residents, however, will be able to keep living in the tower throughout the process.
"The residents won't experience any effects of the construction," Elmets said. "It will affect the sidewalk on one side of the building, but generally the hope is to make it as unobtrusive as possible."
The tower's construction has been the focus of several lawsuits in recent years, which have cost taxpayers.
In October, the city released a study titled "The Tall Buildings Safety Strategy," commissioned by new Mayor London Breed to address options to fix construction flaws in the Millennium Tower and the nearby Salesforce Transit Center.
The report suggested retrofits to fortify what would be some of the city's most vulnerable structures when a major earthquake strikes. An expert panel convened by the city and county deemed the Millennium Tower seismically safe under the city building code, and said settlement hadn't changed its "capability of resisting major earthquakes."
Philip Aarons, a principal at Millennium Partners, said the retrofitting would make the tower one of the safest buildings in California.
"We have made clear from the beginning that getting to a 'fix' has been Mission Street Development's top priority," Aarons said. "This plan will relieve pressure on the soils and will reverse much of the tilt. It will also increase the building's already superior performance in the event of a major earthquake."
In a statement emailed to UPI Tuesday, the city of San Francisco said it has experts reviewing the homeowner's plan.
"Public safety is our top priority. We will process these permits expeditiously with peer review from experts and thorough analysis by city agencies," the statement said. "City departments will work with the homeowners to ensure the structural fixes will protect all residents and the public."
Elmets said there's broad support among homeowners and residents of San Francisco to resolve the issue and restore value to the Millennium Tower.
"We're hoping that the city and the county will move quickly in approving the permit, although we do understand that it does take time," he said. "We are very eager to get started."