Hamburger halted the repairs in August 2021, after the voluntary fix, designed to stem the total of about 18 in. The revised scheme is a consequence of problems with the initial pile work, executed by Legacy Foundations, a division of Shimmick Construction Co. "The city that means and methods" and doesn't care about the order as long as all the load is transferred by the end of the project, he adds. Hamburger says the revised permit did not specifically address the phased load transfer. The entire installation and load transfer operation permit was approved and issued upon review by DBI and also the city's independent engineering design review team (ERDT), according to Patrick Hannan, DBI's communications director.
Last August, after more than six months of scrutiny, the San Francisco Department of Building Inspection issued a revised building permit #202107194668 for the revamped perimeter pile scheme.
Millennium tower sinking pictures upgrade#
The revised upgrade consists of the 18 piles to bedrock, all of which were installed last year, rather than the original 52. A third and final jacking operation will load all 18 piles to 1,000 kips, says Hamburger. The second jacking operation, likely to take place in June once the Fremont collar cures, will load 500 kips on each of the 12 piles along Fremont. In the progress report, Hamburger explained that the purpose of the first stage of loading was to stabilize the building during the remaining construction, which includes the Fremont trench and casting the second collar to tie in the 12 piles under the sidewalk there. The goal is to transfer 17% of the total building load to the 18 new piles, says Hamburger. So far, workers jacked approximately 1,500 tons, or about 1.5% of the building's weight, onto the six new piles in the trench. The removal of another 2,500 tons of soil on Fremont Street will also help, he adds. The 25-ft-deep trench excavation for the collar under the sidewalk on Mission Street also helped with the recovery by removing 1,000 tons of soil, says Hamburger.
Egan is the upgrade’s geotechnical engineer-of-record.ĭuring the incremental and synchronous jacking over the course of last week, the building recovered a part of the accumulated tilting, both to the north and west, and raised up slightly, said Hamburger in the report. “John Egan’s best estimate of tilt recovery, following the final stage of load transfer, is 4 inches west-to-east and 3 inches north-to-south," he adds. And it had settled about 18 in., according to Hamburger. Over time the building had tilted to the west about 28 in. The piles support a new mat section, known as a collar, that ties the existing mat to the new piles. The fix, likened to putting a bumper jack next to a flat tire, relies on drilling and jacking the 18 concrete piles-socketed more than 30 ft into the bedrock that starts 220 ft below grade-under the sidewalks along Mission and Fremont streets. The voluntary upgrade involves transferring a portion of the building weight to bedrock from the existing foundation system via 18 new piles to bedrock. “Preliminary data shows this has been successful and exceeded the engineering team’s projections.” 29 progress report to the board of the Millennium Tower Association. Hamburger, the consulting principal with Simpson Gumpertz & Heger (SGH) who is the engineer-of-record for the upgrade, wrote in a Jan. “Our expectation was that this first small stage of load transfer would slow substantially, if not stop, the already recently reduced rates of settlement and tilting that has been occurring,” Ronald O.
Crews successfully completed the initial stage of the transfer of loads from the residential condominium-which has been settling since its completion in 2009-to six new piles to bedrock installed along one side of the building. The team for the revised perimeter pile upgrade-intended to stem and recover some of the settlement and tilt of the 645-ft-tall tower-reached a milestone last week. If all continues as expected the saga of not just the fix, but the fix of the fix, for the troubled Millennium Tower in San Francisco may be over by the end of September.
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