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

November 2019

Salus, the tunnel boring machine, has made steady progress in its launch from the airport access shaft, located at Shoreway Road and Holly Street in San Carlos. To recover Salus from the launch shaft at the end of the first tunneling drive, we built a retrieval shaft at the north end of Inner Bair Island. Excavation of the soil within the support walls of the retrieval shaft is ongoing.

Barnard-Bessac Joint Venture (BBJV), the tunnel design-builder, completed the first stage of Salus’ assembly below ground in the launch shaft and starter tunnel. This work included installing rails on the bottom surface of the shaft for gantries, the trailing platforms that provide mobile support systems that

help Salus operate as it progresses. These gantries serve various functions. They house all the equipment needed to power and run Salus and provide an entry way for the concrete support ring segments to be delivered for installation. As Salus advances through the soil, it leaves a set of connected concrete rings, constructed of specially formed concrete segments, that make up the excavated tunnel support system. The support system includes a biologically inert grout that is injected into the space between the outer surface of the concrete support rings and the surrounding soil to provide a complete connection of the tunnel support to the excavated tunnel. Part of Salus’ operation involves the removal of muck, which is the term for excavated material. A conveyor system removes muck from the tunnel face and sends it to the launch shaft for disposal via a conveyor system.

To see this process in action, please view the short video from Herrenknecht, the manufacturer of Salus, at the bottom of the RESCU website (svcw-rescu.org). The video shows how a tunnel boring machine similar to Salus operates.

Gantry rails installed
Excavated material entering the muck pit prior to hauling offsite














A gantry on the surface prior to placement in the tunnel

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Gravity Pipeline Project

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