Work done by Legacy Foundations and Shimmick on San Francisco’s Millennium Tower was recently featured in ENR for reaching the final stage of “final stage of load transfer, which consisted of raising all 18 piles to 1,000 kips each, again 100 kips per day.” Major points of the article include:
- The voluntary effort to address settlement and tilting issues in San Francisco’s Millennium Tower has been declared a success. The project involved transferring loads to 18 new perimeter piles driven to bedrock, and survey data confirms that settlement has been arrested, and the building has even slightly risen out of the ground.
- The foundation upgrade project faced challenges due to accelerated movement during pile production, which led to a moratorium and the need to alter pile-driving methods. This, in turn, required a redesign to keep the project on budget and schedule.
- The city’s independent team of engineers overseeing the fix agrees that the retrofit design was well-conceived, and they expect to see the effects of the stressing on settlement and tilt over time.
- Throughout the project, the safety of the 58-story building was not a concern, as early studies confirmed its structural integrity. The revised upgrade involved transferring a portion of the building’s weight to the new piles socketed into bedrock.
- The pile installation caused additional movement, which prompted a halt in repairs and the development of a revamped pile-driving method. The team ultimately settled on using 18 piles instead of the original 52, which allowed the project to be completed within the available time slot. The entire operation is expected to conclude by late August or early September.
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