30 FEBRUARY 2025 WorldWide Drilling Resource® The Biosolids Digester Facilities Project Adapted from Information by SFPUS and Malcolm Drilling The multibillion dollar Biosolids Digester Facilities Project is replacing and relocating the San Francisco Public Utilities Commission's (SFPUC) outdated existing solids treatment facilities with more reliable, efficient, and modern technologies and facilities. Malcolm Drilling was chosen as the Foundation Trade Core partner after an intense prequalification process. Malcolm Drilling was involved in the preconstruction and construction phases 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, developing the design, and meeting the SFPUC budget and construction schedule from an early stage, proved to be a remarkable success for the project. The foundation and site dewatering package included various deep foundations and SOE techniques, such as cased drilled shafts, continuous flight auger (CFA) piles, diaphragm walls, tie-downs, tiebacks, bracing, mass excavation, earthwork, as well as asphalt, shotcrete, demolition, and dewatering. Working closely with the project’s construction manager/general contractor and their main subcontractor, Bertco Inc., as well as two concrete suppliers (Central and Cemex), was the key to the successful delivery of this massive project. Malcolm installed over 140 48-inch-diameter CFA piles up to 80 feet deep and 200 36-inch-diameter CFA piles up to 70 feet deep, bringing considerable schedule and cost savings to the project. Where the future structure was belowgrade and CFA piles were not a viable option, the company also installed over 210 48-inch-diameter drilled shafts up to 100 feet deep, utilizing temporary steel casings to stabilize the weak bay mud soils during drilling. From their highly specialized fleet of equipment, Malcolm utilized several of their BAUER drill rigs, Leffer oscillators, Putzmeister boom pumps, and Liebherr cranes to complete the work. The SOE wall included over 600 tiebacks with lengths of up to 80 feet. They were installed at 30-degree angles with sufficient length to create a bond zone in the competent upper layers of sediments that exist beneath the young bay mud. Water treatment and dewatering were also required for two deep building excavations as part of this project. Malcolm performed an early dewatering pump test program to help guide the design of the SOE system and its potential effects on the two nearby active railroad tracks. In total, Malcolm designed and installed 50 dewatering wells targeting three different aquifer zones, so mass excavation could safely occur without the risk of bottom heave. Malcolm also installed 12 observation wells to monitor groundwater levels outside the excavation. With 600,000 hours of work on-site, the Biosolids Digester Facilities Project earned the Occupational Excellence Achievement Award from the National Safety Council. When asked how the Biosolids Project maintains such an outstanding record, Biososolids Project Safety Manager Jorge Torres said, “This award was earned by everyone - whether they attended a safety walk, or noticed something and spoke up, if they posted an observation on the safety portal, or even just reminded someone to put their safety glasses on. This is something tangible for us. It’ll help us keep striving to do even better but also to continue this level of excellence each year.” SFPUC’s Construction Management Bureau Manager Algy Collymore noted the achievement: “We want to congratulate the Safety Program and the entire team for continuing to work safely and efficiently. This award highlights the benefits of the city’s focus on safety through the prebid Contractor Safety Evaluation process and selecting contractors with a track record of working safely. Well done!” CONST
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