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

April 2019

The RESCU Gravity Pipeline project team made a trip to the Herrenknecht factory in Germany to witness the factory acceptance test.  The trip was a huge success and we’re very happy to report that the TBM manufacture is on track and looking good.

What does a Factory Acceptance Test entail? 

During the Factory Acceptance Test the machine and all of its trailing gear is assembled inside of a warehouse to demonstrate how everything fits together. Depending on the diameter of the tunnel machine the trailing gear will be longer or shorter. The larger the diameter the shorter the gear because more can fit vertically in each section (imagine a train that is one story high versus one that is three stories high). Then the technicians and engineers from the factory and those from the Design Build team test the different elements of the machine operations. As an example; the segment erector sets each concrete segment in place around the tunnel inside, so it must pick up, rotate and push outward to set each of the six segments that make up an entire ring. In the factory they cannot actually build a tunnel, so they use a metal piece shaped like a typical segment and manipulate the erector to show that it can perform the work once it is on site. This continues for several days and weeks to test the various pumps, electrical and hydraulic equipment that will end up on the project site and working to build our tunnel.…

We’re still on schedule with an anticipated delivery date in early July 2019.  The TBM will be disassembled at the factory and then shipped via ocean vessel through the Panama Canal, off-loaded and delivered to the launch shaft site in pieces since it is 16-feet in diameter and 600-feet long.  The shipment will arrive in Port Hueneme, CA, near San Diego and trucked to the launch shaft.  Piece-by-piece the design build team will lower it into the launch shaft (which is 60-feet in diameter) and the TBM will be re-assembled at the bottom of the shaft.  As the pieces are reassembled in the shaft, the machine will begin to move and tunnel toward Inner Bair Island. As enough space in the shaft is available another section will be lowered, assembled and connected to the section ahead to make the train that will move through the tunnel toward the exit shaft.

In other Gravity Pipeline activities, work is ongoing to excavate the launch shaft and inclined conveyor shaft. As the tunnel machine moves forward the dirt it excavates must be moved to the back of the machine and out of the launch shaft. Our particular site is smaller than most, so we made a choice to use conveyors instead of trains to move the excavated soil. There will be a conveyor inside the tunnel the entire length behind the tunnel and up an inclined conveyor to get the dirt to the surface. We will begin the inclined conveyor tunnel installation this week. The next piece of work will be to start building the temporary access road and exit shaft on Inner Bair Island. This will begin in early June of this year. 

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