Silicon Valley Gravity Pipeline

With the significant population growth in the San Francisco Bay area, the Silicon Valley Clean Water’s (SVCW’s) wastewater conveyance authority that serves more than 200,000 customers sought replacements for their aging and increasingly unreliable system. One part of SVCW’s Regional Environmental Sewer Conveyance Upgrade (RESCU), is the gravity pipeline project that includes the design and construction of 3.3 miles of a 16-ft-dia. gravity pipeline TBM-bored tunnel. In a progressive Design-Build agreement with contractor Barnard Bessac JV, and design engineer Arup the staged project will have a 100-year design life and a 10-year design life warranty,

Malcolm was responsible for the support of excavation for 85 ft-deep, 60 ft in diameter, Tunnel Boring Machine (TBM) access shaft. The shaft was constructed using a structural reinforced concrete slurry wall consisting of slurry wall panels, each excavated under bentonite slurry to design depth and connected to the next panel by construction joints. Excavation of individual panels was performed under bentonite slurry. Once excavation was completed, the slurry was cleaned, rebar cages installed and tremie concrete was placed through tremie pipes. Big challenge was the actual site logistics that led to complex task scheduling. While the site in general is large, the location of the shaft was constrained by power lines to the west that limited the usage of the site to east of the power line. Moreover, FAA regulations required limited headroom for construction equipment which required equipment and reinforcement to be configured in low headroom configuration, since the site was located less than half a mile north of San Carlos Airport.

Malcolm Drilling