San Francisco’s Millennium Tower ‘fix’ takes jaw-dropping next step – NBC Bay Area
Work began this week on a new phase of the renovation of the sinking and tilting Millennium Tower – an operation which one critic describes as “very risky” because it involves digging and removing tons of earth from support on both sides of the already troubled foundation.
Millennium Tower officials informed residents in a memo on Tuesday that construction work is entering the fourth and final stage, with excavation work required to extend the existing carpet foundation which will be supported by new piles of supports anchored in bedrock. Residents have been told to expect “drilling noises” as well as vibrations associated with the work, which is expected to last until September.
As work on this final stage begins, monitoring data shows the tower leaning 27 inches to the northwest at the top. Since work began in May, the tower has tilted an additional 10 inches at the top, according to this monitoring data.
Millennium Fix designer Ron Hamburger has said the building is expected to tilt a little more by the time the work is complete, but experts fear that the new digging to make way for an enlarged foundation could sink and collapse. tilt the building more than expected.
“I think it’s very risky,” said veteran local geotechnical engineer Bob Pyke, who has repeatedly warned city officials about the viability of the solution. In a March 14 letter to building manager Neville Pereira, Pyke wrote, “I now warn that there are many uncertainties associated with the excavation required to construct the mat extensions.”
Pyke says he fears digging 25ft and removing dirt from both sides of the structure – where it currently leans the most – will mean the loss of earth that is currently reinforcing the existing foundation. He says the work could result in up to two inches of additional settlement. This equals how much the building has sunk since the so-called repair began. This work-related settlement resulted in about 10 inches of extra tilt.
“It could be anything from zero to six inches – I don’t know,” Pyke said of the amount of settlement the building could experience around the corner. “That’s the problem – no one knows.”
City officials said in a statement that they will stop digging if settlement during construction exceeds established limits. But they pointed out that despite the new phase of work, the city has yet to approve the Millennium Fix engineer’s plan to use just 18 piles to support the building instead of the 52 originally planned.
While residents of the tower were alerted to the prospect of additional noise, several told the NBC Bay Area Investigation Unit that the constant jackhammer work so close to their windows was heartbreaking. Millennium officials told them to expect work to continue between 7 a.m. and 8 p.m. on weekdays and sometimes on weekends as well.