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 May 2022

Following installation of the fiberglass reinforced polymer (FRP) pipe inside the gravity tunnel, SVCW’s contractor partner for the Gravity Pipeline project, Barnard Bessac Joint Venture (BBJV), has completed installation of the last set of connection pipe segments inside the Airport Access Shaft (AAS). These pipes connect Tunnel Drive 1 to Tunnel Drive 2, and mark the successful completion to the construction of the conveyance portion of the Gravity Tunnel Project. BBJV also performed inspection walks in the tunnel to inspect the finished pipes. The Airport Access Shaft has now been prepared for backfill, with the crew all set to place backfill to support and protect the completed pipe in the shaft, followed by backfill of the Airport Access shaft to match the existing ground surface elevation.

Construction work also progresses on schedule at the San Carlos Pump Station (SCPS) site. BBJV has completed installation of the new drop structure that connects Belmont and San Carlos collection systems to the gravity tunnel. The shaft wall section has been prepared in a way that provides an inlet for new piping to carry collection system flows into the new drop structure, and into the gravity tunnel. Current work includes placement of the Fiberglass Reinforced Polymer drop structure and backfill of the shaft to grade to support the drop structure in the shaft. Completing the backfill operation will be the final step in the shaft construction for the gravity tunnel connection at San Carlos. The Bair Island shaft has been completed with the installation of the Bair Island Drop Structure, following backfilling of the shaft and removal of sheet piles that supported the shaft during construction. BBJV continues to maintain consistent coordination with its subcontractors and inspectors on each site, to ensure crew safety.

As the Gravity Pipeline project is in its last phase of work, with backfill of the AAS and installation of the drop structure to connect flows from Belmont and San Carlos, SVCW and BBJV are working together to coordinate for the startup of the system. Over at Front of Plant, the break-in site for Salus, the tunnel boring machine (TBM) that mined the 3.5-mile long tunnel, was dismantled and demobilized from the RESCU program in Fall of 2021. Looking at how far the project has come, with final site restoration beginning this month, the Gravity Pipeline project team continues working towards a safe and successful startup of the project.

 

AAS shaft pipe installation

 

AAS shaft completed pipe

 

Drop structure being placed in shaft at San Carlos connection to the gravity tunnel

 

Bair Island Drop Structure air inlet lamination

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