The $2 billion Biosolids Digester Facilities Project (BDFP) being constructed for San Francisco Public Utilities Commission (SFPUC) is located in southeast San Francisco. Working within a confined site bounded by active Caltrain and Union Pacific Railroad tracks and the existing Southeast Treatment Plant (SEP) posed construction sequencing and geotechnical challenges. This complex mega infrastructure project will replace and relocate the outdated existing solids treatment facilities with more reliable, efficient and modern technologies. Early involvement of core trade subcontractors by the CMGC, including foundation core trade partner Malcolm Drilling with Brierley Associates, resulted in early identification of site challenges. Through weekly meetings with the CMGC, SFPUC and their design team, the foundation partner was able to provide value engineering solutions on several major scopes of work. One example is the use of continuous flight auger (CFA) piles at certain structures, in lieu of the more traditional drilled shafts, which brought immediate schedule and cost savings to the project. In order to verify the capacities of the CFA piles and drilled shafts, the team performed an early-work onsite load test program, which gave the SFPUC design team confidence in the pile foundation selection. Additionally, Malcolm implemented an early-work onsite pump test program to provide the SFPUC design team with more information about groundwater flow regime. This test discovered two interconnected aquifers and led to constructing a temporary diaphragm wall system rather than a cutter soil mix (CSM) shoring at Facility 610.
In this article in Deep Foundations Magazine, Brierley’s Amshu Chappa, PE, and Malcolm Drilling’s Robert Small, PE, and Ihab Allam, PE, detail these and other challenges and solutions, utilizing all of the tools in their toolbox.