The 717 Battery Street project, in the Jackson Square District of downtown San Francisco, is located on the old waterfront of the city and presented several challenges. This particular structure was built in the 1800’s, was retrofitted in 1910 after the 1906 earthquake, and required seismic strengthening.
For this 3-story, unreinforced masonry timber pile supported building, Malcolm installed a micropile foundation for the seismic strengthening, and hand-mined piers for the structural underpinning of the masonry walls and timber columns to facilitate the deepened basement below the existing basement. Additionally, drilled soldier piles supported with tieback anchors and internal braces were installed for the expansion of a new basement expansion under a plaza.
The steeply sloping bedrock, high groundwater table, soft clay on top of rock, confined work spaces, and strict project requirements, all presented unique challenges on this project. To “pick-up” and shore the individual timber columns in the basement, our crews had to build small cofferdams in very tight conditions. These cofferdams around the base of each column were installed in a phased sequence to facilitate dewatering as the original columns were jacked up to allow for the old concrete pile caps to be removed and replaced.