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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Gravity Pipeline Project

Last Updated July 2021

TBM Status Update – July 2021

Another Month of Good News! Salus, the mighty tunnel boring machine (TBM), has successfully completed its second tunneling drive and has tunneled into the receiving shaft located at the Front of Plant. Even more good news, having tunneled approximately 13,000 feet from its launch shaft at the intersection of Shoreway Road and Holly Street, Salus has once again reached its destination on time and on target at Silicon Valley Clean Water (SVCW)’s Wastewater Treatment Plant. This is the second major milestone for the Gravity Pipeline project team since Salus’ first break in on Bair Island that happened at the end of March 2020.  Congratulations to the tunneling team and everyone who participated in supporting the effort!


To prepare for the break in, SVCW’s contractor partner, Barnard-Bessac Joint Venture (BBJV), prepared the receiving shaft wall by using road header equipment to perform a partial demolition of the wall, limited to the specific section where Salus would be entering the shaft. The demolition work reduced the extent of the concrete wall that the Salus needed to mine through during the break in to the shaft, while still ensuring the integrity and strength of the shaft wall is maintained.

For a safe break into the shaft, BBJV had backfilled the shaft with a mix of water and soil to mimic the underground conditions that Salus had been used to tunneling through. With the breakthrough step completed, BBJV will be excavating the soil from around Salus to allow the start of the process of removing Salus, section by section, together with its supporting equipment (referenced as gantries) from the tunnel and shaft.


Upon removal of Salus from the shaft, BBJV will be installing 11-foot diameter Fiberglass Reinforced Plastic (FRP) pipe sections within the completed tunnel. These pipe segments will be installed and assembled within the completed tunnel to form the carrier pipe that will carry raw wastewater to SVCW’s treatment plant by gravity.

Having to work through COVID-19 from the end of the first tunneling drive through the second tunneling drive SVCW and BBJV have done a great job in keeping up with all health and safety measures and protocols while adjusting work procedures to ensure that tunneling production was safe and on schedule.

Again, another big CONGRATULATIONS to SVCW and RESCU’s Gravity Pipeline project team!

Monthly Update: June 2021

As of June 14, 2021, Salus tunneled 12,208 feet from its launch shaft and built  2,437 rings. Tunnel production towards the Front of Plant (FoP) project site continues, as the date for TBM break-in to the receiving shaft approaches. The Surge/Flow-Splitter shaft (SFS) element of the FoP project is serving as the TBM retrieval shaft before being repurposed to be part of the FoP project.

BBJV will perform demolition of a portion of the SFS Shaft wall, limited to the specific section where Salus will be breaking through. This demolition will reduce the extent of the concrete wall that the TBM will need to mine through to break in. The demolition work follows a planned approach to ensure safety of the break-in operation. 

Once partial wall demolition work is complete, BBJV will fill the SFS shaft with soil and water to allow Salus to mine into the SFS under safe conditions, like the mining conditions Salus has encountered over the 3.5 miles of mining completed so far.  

As Salus enters the final stretch of mining, BBJV is keeping up with its daily tunnel task force and check in meetings where the real-time TBM and mining parameters are discussed in detail. 

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