Silicon Valley Clean Water Gravity Sewer Tunnel Project

Project: Silicon Valley Clean Water Gravity Sewer Tunnel
State: California
Pipe Type: CW FRP
Length (ft): 17,500
Diameter: 132"
Pressure (PN): 6
PSI: 87
Installation Type: Sliplining
Use: Sewer Tunnel

ISI delivers the largest FRP pipe shipment in US history delivering a cost-effective, quality wastewater solution to Silicon Valley Sewer Tunnel Project.

Infrastructure Solutions International (ISI) and Future Pipe Industries have supplied the largest overseas shipment of fiberglass-reinforced plastic (FRP) pipes to California’s Silicon Valley Clean Water sewer upgrade project, which includes a requirement for a wastewater gravity pipeline with a design life of 100 years. 

Silicon Valley Clean Water (SVCW) owns and operates the San Francisco Bay area’s wastewater conveyance system and wastewater treatment plant. It serves over 200,000 people and businesses in the area and provides recycled water to Redwood City, California. 

Due to population increases and increased regulatory requirements, the organisation needed to upgrade its 45-year-old sewer conveyance system with a new gravity pipeline tunnel that would have a design life of 100 years. 

The new pipeline project forms part of the Regional Environmental Sewer Conveyance Upgrade (RESCU), which consists of the design, construction and commissioning of a 16 foot, 3.3 mile concrete-segment wastewater gravity sewer tunnel specially designed to house the fiberglass-reinforced plastic (FRP) pipeline.

The tunnel will be constructed using a tunnel boring machine (TBM) from the north edge of Inner Bair Island to the new facilities at the front of the treatment plant. 

The pipeline tunnel will be constructed at varying depths depending on above-ground and underground infrastructure requirements, with sections of the tunnel varying between 20 to 60 feet below ground. Tunneling is being used as an alternative to open-cut installation methods so that ground disturbances are minimised and long distances can be allowed between shafts. The work includes three shafts. 

FRP pipe will then be installed in interlocking segments within the tunnel as the gravity carrier pipeline to convey raw wastewater. Once constructed, the pipeline will enable the safe and reliable transport of wastewater from four member agencies’ collection systems to the treatment plant. 

Pipe selection process 

SVCW engaged the Barnard-Bessac Joint Venture (BBJV) to complete the works via a progressive design-build agreement. As part of the agreement, and in addition to the 100-year design life, the joint venture has provided a 10-year design life warranty. 

BBJV had to meet SVCW’s requirements to deliver on: 

  • Quality: by providing a gravity pipeline that will be sustainable over 100 years and will reliably receive, convey and equalise wastewater flows ranging from 2 million gallons per day (MG/d) to 103 MG/d in full compliance with environmental requirements.  
  • Cost: by providing a complete functional gravity pipeline and inlet facilities that meet the goals of the project at the lowest practical capital and lifecycle cost. 
  • Schedule: by achieving the best practical safe speed to complete the tunnel and inlet structures so that the existing failing pipeline and pump stations can be taken out of operation as early as reasonably possible. 

The BBJV team, along with pipeline design engineering firm Arup, evaluated several cost-effective design alternatives for a corrosion-resistant lining that would require minimal maintenance over a 100-year period. 

The team chose FRP pipe because of its cost-effective installation, resistance to corrosion, strength-to-weight ratio, low-cost maintenance, and longevity.

Thinking outside the box to deliver record-breaking pipe supply

FRP pipe manufacturer Future Pipe Industries (FPI) produced 17,000 feet of its Fiberstrong FRP pipes and double bell coupler joints in both 10 foot and 11-foot diameters – representing the largest diameter fiberglass pipe to be used in a North American project to date. 

FPI manufactured the pipe under tight quality control guidelines at its Indonesian factory. Infrastructure Solutions International (ISI) then arranged for the pipe to be transported safely to site in the US. 

ISI Managing Director Andy Holman says “Producing that volume of large FRP pipe in itself is a challenge. Moving 50,000 cubic meters of pipe from a factory in Indonesia to a project site in Redwood City, California, is no small task either.  It has been the largest overseas shipment of FRP pipes to date.”  

ISI chartered two separate shipments using Western Bulk’s Interlink Sagacity bulk carrier. The carrier vessel measures 180 m length overall x 32 m breadth extreme. .  

Despite the vessel’s impressive size, ISI had to find a creative way to ensure that the large pipe shipment was transported in the most efficient manner. 

“We nested all of the 10-foot diameter pipes in the 11-foot diameter pipes,” says Holman. 

“This maximised freight efficiency, saving our client time and money, and it also served to protect the pipe during transport.” 

ISI also arranged tproject-specific alterations to the vessel, both internally and on the deck/hatch covers, so that the safe delivery of the pipe could be ensured.

“We typically choose to work with suppliers who run large scale operations as this ensures efficiencies in price and a greater guarantee of quality,” says Holman. “So we’re used to arranging big shipments. But this project has been a career highlight. We’re proud of the challenges that we’ve overcome to deliver the latest overseas shipment of FRP pipe.” .

Let’s delve into the BBJV’s decision to use FRP pipe on the RESCU project in a little more detail.

What makes FRP pipe so durable?

FRP pipe is manufactured by continuous winding processes that use vinyl ester resins in the inner layer of the pipe, reinforced with continuous glass filaments. This process improves crack resistance and enhances the design life of the pipe. The resins used undergo irreversible chemical reactions as they cure (thermosetting). 

An outer vinyl ester coating also ensures that the pipe can withstand the rigors of grouting. The overall result is a more durable and light-weight product than other pipe materials.

 What are the benefits of using FRP pipe for wastewater projects?

Historically, wastewater pipelines were traditionally made from concrete, but FRP pipe has proven to provide advantages over concrete during installation and over the design life of the wastewater system. 

FRP pipe has better hydraulic performance than concrete pipe thanks to its smooth internal surface. This helps with the flow of the wastewater through the pipe. 

In addition, FRP pipe is corrosion-resistant and does not require steel reinforcement. On the other hand, concrete pipes do require steel reinforcement and have the potential to corrode. 

Concrete pipe can also deteriorate quickly when used in sewage applications due to hydrogen sulfide, which erodes the upper surface of the pipe and can eventually cause the pipe to cave-in. FRP is unaffected by hydrogen sulfide, and its vinyl ester resins provide excellent resistance to water, organic solvents and alkalis. 

FRP pipe is also easier to transport thanks to its lightweight properties, providing further cost savings.