Design-Build for SFPUC Biosolids Digester Facilities Project
San Francisco Public Utilities Commission (SFPUC) is a department of the city that provides drinking water and wastewater services to San Francisco along with, green hydroelectric and solar power to San Francisco municipal departments.
SFPUC decided early in the process to use an alternate delivery method to utilize the expertise of the entire construction industry by engaging Trade Core partners at an early stage in the design-build process. Malcolm Drilling was chosen to be the Foundation Trade Core partner, after an intense pre-qualification process.
We worked on the pre-construction and construction during the design and construction of all deep foundations and Support of Excavation (SOE) for various structures of the Biosolids Digester Facilities Project for the SFPUC Sewer System Improvement Program. Malcolm working as a trade core partner, developing design, and meeting the SFPUC budget and construction schedule from an early stage, proved to be a remarkable success to the project.
The foundation and site dewatering package included various deep foundations and SOE techniques including Cased Drilled Shafts, Continuous Flight Auger (CFA) Piles, Diaphragm Walls (D-walls), Tie Downs (Micropiles), Tie Backs, Bracing, Mass Excavation, Earthwork and Asphalt, Shotcrete, Demolition and Dewatering. Coordinating the various scope of works that Malcolm self performs was another challenge for us. Working closely together with the projects CM/GC (a JV of Webcor and MWH constructors) and our main subcontractor Bertco Inc., as well as two concrete suppliers (Central and Cemex) in a real partnership was the key to the successful delivery of this massive project.
The support of excavation (SOE) wall for building 610 included over six hundred tiebacks with length of up to 80-feet. All tiebacks were installed at 5-feet on center and had design loads of up to 245 kips. They were installed at 30-degree angles with sufficient unbonded length to create a bond zone in the competent upper layers of sediments that exist beneath the young bay mud. The tieback strands varied from five to ten strands across the entire excavation. The tiebacks were installed through pipe block outs that were pre-installed within the D-Wall rebar cages.