Silicon Valley Clean Water Gravity Pipeline Project

The Silicon Valley Clean Water (SVCW) Gravity Pipeline Project shines a spotlight on a process that is typically out of sight and out of mind: wastewater transportation. SVCW undertook this project as part of a $580M Regional Environmental Sewer Conveyance Upgrade (RESCU) Program to rehabilitate and convert its 50-year-old raw wastewater conveyance system at the end of its useful life from a force-main system to a gravity conveyance system.

The project consisted of the design and construction of 3.3 miles of fiberglass reinforced polymer mortar (FRPM) pipe inside a concrete-segment Tunnel Boring Machine (TBM) tunnel and three shafts. SVCW wanted a new system to serve the public, support community health and protect the environment for 100 years.

A “Boring” Solution to Minimize Community and Environmental Impacts

In June 2021, a 16-ft.-diameter TBM mined through a concrete shaft, completing its 3.3-mile journey beneath an airport taxiway, a major suburban thoroughfare, an active and aging sewer force main, and two local residences. SVCW used TBM technology to avoid disrupting surface uses along the entire alignment. By boring a tunnel and installing the large-diameter pipe underground, SVCW significantly reduced community and environmental impacts along the San Francisco Bay Margin.

One of the project’s more unique requirements involved the intricate design and construction of two vertical drop structures where existing municipal sewers connect to the new pipeline. With a drop of up to 30-ft. in elevation head, these structures act as a means of potential and kinetic energy dissipation and conveyance.

Arup used hydraulic analysis to demonstrate viability of reducing approximately one-third of the pipeline length to a 10-ft. internal diameter. This allowed for the nesting of the smaller-diameter pipe inside of the larger-diameter pipe during transportation from the fabricator in Indonesia, saving approximately $1 million in transportation costs and providing a massive reduction in carbon footprint.

The SVCW Gravity Pipeline Project became the first TBM project in North America to be completed using Progressive Design-Build (PDB) as the project delivery method. Despite challenging ground conditions and a global pandemic, the project finished on time and on budget, an outcome SVCW largely attributes to the collaboration fostered by PDB. It was also SVCW’s first design-build project, and its success paves the way for future projects at the authority as well as the tunneling and wastewater treatment industries at large.

Design-Build Team

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