Abstract:
Creating A Resilient New Waterfront Neighborhood in San Francisco
Mission Rock Phase 1 Development, San Francisco, California
By: Peter Brady, PE, GE, Noel Jose, PE, Scott A. Walker, PE, GE, and Lori A. Simpson, PE, GE.
Mission Rock is a new waterfront neighborhood in San Francisco. Currently under construction, Phase 1 consists of two, 240-foot-tall residential high-rise buildings, a 120-foot-tall and a 210-foot-tall commercial building, a waterfront park, and new public streets and infrastructure. The site is located along the San Francisco Bay and was originally below water in a shallow bay, which was reclaimed between 1880 and early 1900’ s. The site is blanketed by liquefiable fill underlain by compressible Bay Mud. The site is in zone of high seismicity, located between two major faults. The future sea level is predicted to rise as much as 66 inches by the year 2100, which would submerge the site during a high tide. The project developers are committed to constructing this development to be resilient to earthquakes and sea level rise. Accordingly, liquefaction and sea level rise required mitigation.
Liquefaction was mitigated with stone columns. Wick drains were installed between columns to dissipate pore pressures that are developed during stone column installation and allow for increased densification of the liquefiable fill.
Sea level rise was mitigated by raising new streets by as much as 5½ feet. If conventional fill was used to raise grades, the new fill load would cause as much as 2 feet of consolidation settlement in the Bay Mud; which would affect not only public infrastructure but also design of the buildings’ deep foundations. A number of options were considered to allow for raising grades without causing settlement. Ultimately, the team selected to offset the new loads by overexcavating existing fill and raising grades using lightweight cellular concrete (LCC), which had never been used within a public street in San Francisco.
This paper will address the challenges of design, approval and construction of the public infrastructure improvements to be resilient to natural hazards using methodologies and materials that had not been previously approved by the City of San Francisco and the Port of San Francisco. We will present the results of test programs, as well as the QA/QC process of both the ground improvements and the LCC.