Shimmick performed mass excavation and shoring for the foundation of two separate towers in downtown San Francisco at the corner of First and Mission. Tower 2 is approximately 14,000 square feet at a depth of 58.5 feet below grade with three levels of full bracing consisting of struts and walers and a partial 4th level in the NE corner tying into Tower 1. Tower 1 is approximately 37,500 square feet at a depth of 66 feet below grade with four levels of full bracing.
The scope also included pre-stressing the bracing, excavation and bracing in elevator pits, and CSM buttress shaft demolition. The project included approximately 130,000 cubic yards of excavation and over 5.8 million pounds of steel bracing.
Shimmick closely coordinated with the shoring designer to re-sequence the original jacking sequence to allow for continuous excavation and bracing operations to take place simultaneously. This allowed Shimmick to maintain smaller and more efficient crew sizes with both operations that provided consistent schedule flow and ultimately shortened the excavation and bracing activities by weeks.