What is the Gravity Pipeline Project?

The Gravity Pipeline (GP) Project consists of the design, construction, permitting, start-up, commissioning, and closeout of approximately 17,600 feet of wastewater gravity FRP pipe inside a concrete-segment tunnel. The work includs three shafts and will interface directly with the Front of Plant (FoP) Project at the Receiving Lift Station (RLS). Work is being implemented under a Progressive Design-Build procurement process.

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What's Happening

Gravity Pipeline Project

Last Updated September 2021

Silicon Valley Clean Water (SVCW)’s contractor partner, Barnard-Bessac Joint Venture (BBJV), is finishing up work at the Surge and Flow Splitter (SFS) shaft, located on the western side of the Front-of-Plant (FoP) Project site. Salus, the Tunnel Boring Machine (TBM), successfully completed its second and final tunneling drive in late June 2021. Approximately two months after a successful break into the SFS shaft, which served as a temporary TBM retrieval shaft, BBJV has removed nearly all of the TBM pieces and support gantries from the SFS shaft and hauled them offsite for use in other tunneling projects not associated with SVCW’s project.  SVCW and BBJV have negotiated the salvage value of the TBM as part of the original design-build contract for the gravity tunnel.

To prepare the completed tunnel for installation of the Fiber Reinforced Polymer (FRP)  wastewater conveyance pipe, BBJV has cleaned the tunnel and, together with the Quality Assurance team, BBJV will be conducting a final inspection of the concrete support rings that were installed by Salus during tunnel construction. As part of the tunnel cleaning process, BBJV removed utilities from within the tunnel that were used to support the excavation and tunneling work, including muck conveyors and air supply ducting.

Cleaned out tunnel
Cleaned out tunnel

At the San Carlos Pump Station site, BBJV is preparing to install FRP piping to connect new piping from the San Carlos and Belmont sewer collection systems to the gravity pipeline tunnel that was built as part of Salus’ first tunneling drive. To do this work, BBJV constructed a shaft on the east side of the existing San Carlos Pump Station structure. The shaft has been excavated to a depth of approximately 50-feet below the ground surface to allow BBJV to install a FRP drop structure and FRP piping to carry raw wastewater from the collection systems for the Cities of San Carlos and Belmont into the gravity tunnel. This month, a tunnel jacking frame will be delivered to the San Carlos Pump Station site, where it will be installed within the shaft to assist with the jacking and installing of the FRP drop structure and pipe segments.

Jacking frame installed within San Carlos shaft
Jacking frame installed within San Carlos shaft


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Gravity Pipeline Project

Gravity Pipeline August 2021

With Salus, the Tunnel Boring Machine (TBM), successfully completing its second tunneling drive, SVCW’s contractor partner, Barnard-Bessac Joint Venture (BBJV),

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