Microtunneled Bypass Pipe Integral to Deer Creek Dam Project
Built more than 80 years ago, the Deer Creek Dam and Reservoir – along the Provo River – is in need of critical updates to ensure its ability to provide water and power to people living, working and visiting Utah’s Wasatch Front.
Owned by the U.S. Bureau of Reclamation and stewarded by the Provo River Water Users Association, the dam and reservoir supply water to more than 1.5 million people and is crucial to Utah’s recreational needs and future growth and economic stability. With that in mind the Provo River Water Users Association began looking at necessary improvements in 2019, with project design commencing in 2021 and construction beginning in 2023.
The $100 million Deer Creek Dam Intake Project upgrades the aging infrastructure to safeguard the water supply from invasive aquatic species, refurbish existing infrastructure and provide redundancy to users.
The association, working with its engineer AE2S, came up with a design to refurbish the dam without bypassing, draining the reservoir or interrupting the water supply. As the preliminary design phase was wrapping up Granite Construction was brought in as the construction manager/general contractor (CM/GC) to complete the final design phase.
Microtunneling the Deer Creek Dam Bypass Pipe
A key component of the project is the installation of a bypass pipeline that allows for the isolation and refurbishment of the existing works and provides redundancy for water deliveries even during times of drought. Oregon-based J.W. Fowler was selected as the tunneling and pipe installation contractor.
J.W. Fowler tunnel division manager Chris Bottoms notes that the company was brought in as part of the CM/GC team to offer input on tunnel design and construction. Through this process the team was able to work collaboratively to design solution that was the least disruptive and had the lowest amount of risk.
“For tunneling projects, which are often complex and high risk, progressive delivery contract models allow an owner to avoid disproportionate fees for risk not yet encountered and provide a constructive amount of transparency and collaboration,” Bottoms says. “The team was able to allocate the risk appropriately without making it a lump sum issue for the client.”
The proposal culminated with the installation of 800 ft of 72-in. OD steel pipeline via microtunneling. The microtunnel started at the base of the dam abutment and moved up to the Deer Creek Reservoir with recovery of the microtunnel boring machine (MTBM) 85 ft below the reservoir’s surface.
Selecting the Right Pipe
Pipe manufacturers were engaged in the bidding process and after much consultation it was decided that Tri-Loc MT-H gasketed microtunnel mechanical joint pipe would be used on this project. The 72-in. OD pipe has a 0.875-in. wall thickness and is coated with 45 mils of Tnemec ARO 425. The latter is an abrasion resistant overcoat applied to the outside of the pipe to protect the steel pipe while its being jacked into place – a critical component as much of the bore was projected to be through hard rock.
This project marked J.W. Fowler’s first use of Tri-Loc pipe fabricated by Trinity’s new Horizontal Boring Mill whereby the MT-H joint was directly profiled onto the pipe to create a seamless pipe body with no circumferential mid-welds of a separately machined and fitted joint piece.
The pipe also met ASTM A252-Gr 3 standards, with modifications to ensure a minimum yield strength of 50 ksi and underwent additional inspection to comply with AWWA C200 standards.
“We’ve used the previous generation of Trinity Products pipe. This was our first experience with Tri-Loc’s new direct-milled ends,” Bottoms says. “The fit up of the pipe worked for us…I can’t help but respect Trinity for advancing the technology. Mechanical joints have been around for some time and to see a company advancing fabrication methods, to optimize the cost of the product…is desirable for all of us in the industry.”
Bottoms notes that to mitigate potential risks of being under 2.7 bar of pressure and the critical nature of this pipeline, J.W. Fowler crews seal welded all joints before being pushed into the seal.
What Is the HBM?
To enhance production, Trinity Products invested $9 million in a cutting-edge horizontal boring mill (HBM), which allows for precise machining of Tri-Loc connections directly into the pipe.
Key benefits of this process include:
Precision: The HBM ensures highly accurate joints that meet stringent industry tolerances. Each product comes with a certificate of compliance, instilling confidence in its performance for trenchless applications.
Consistency: Tri-Loc is manufactured in-house, giving Trinity’s team full control over the process. This ensures the company’s industry-leading quality standards deliver consistent results every time, guaranteeing dependable and repeatable performance even in challenging project conditions.
Efficiency: Trinity’s vertically integrated manufacturing process enhances control over lead times, allowing for greater availability and reducing overall production time by 50 percent.
Microtunneling Under Pressure
To complete the installation J.W. Fowler used a Herrenknecht AVN 1500 MTBM and a custom separation plant. The hard rock microtunnel was portal launched from the base of the dam using a thrust reaction frame built into the ground using rock socketed pile members.
“All mining and separation operations were from below the reservoir’s water surface, headed up under the dam abutment toward the reservoir. The first 1/3 of the project had relatively low water pressures and when we approached the grout cutoff curtain, the water pressure increased significantly,” says Bottoms. “We went from about 0.5 bar of water pressure up to almost 2.7 bar of water pressure through 2/3 of the drive.”
Because the bulk of the bore was under these higher pressures, the project team planned for an atmospheric intervention just before the grout curtain cutoff wall to change out all tooling under a more controlled environment.
“We completed an atmospheric intervention using heading drawdown tests to determine when to stop, ensuring we were in a competent rock formation, and then we went into the head and replaced all tooling while pumping between 80 to 100gpm through the MTBM” he says. “It was unlikely that the tooling would survive a full 800 ft through the hard rock. It was a wise move as we were able to mine an additional 550 ft without changing tooling. The tooling was certainly well-used when it came out on the reception side.”
Completing the Work
“This was a unique project. We were able to complete the installation of the bypass tunnel with the reservoir at full pool without a draw down,” Bottoms says. “A lot of the other potential solutions [discussed] included bypass pumping and or significant drawn down of the reservoir through the summer season.”
J.W. Fowler’s scope of work was complete in September of 2024. The last several weeks of work involved final welding of grout ports followed by internal surface preparation and interior lining of the pipeline using a high-build solids epoxy lining that was completed by a subcontractor.
“Adopting a progressive and collaborative approach upfront, we developed meaningful relationships and an in-depth understanding of all project stakeholders,” Bottoms says. “The progressive delivery approach pays off. We did not fall victim to pride of authorship [of the project] from any of the parties involved. We worked collaboratively to find the best and most optimized design to complete the tunneling component of this project successfully, at the lowest cost, and the lowest risk to the project stakeholders.”
Mike Kezdi is managing editor of Trenchless Technology.
