PROJECT BACKGROUND

In 2022, Knoxville Utilities Board (KUB) discovered severe corrosion in a crucial 2,400 linear feet section of a reinforced concrete pipe (RCP) sewer trunkline beneath a key arterial road, serving as a vital access route to the University of Tennessee’s renowned Neyland Football Stadium and other sports facilities. The trunkline provides influent to the Kuwahee Wastewater Treatment Plant, KUB’s largest wastewater treatment plant.

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Prioritizing proactive infrastructure management, KUB collaborated with their construction manager and engineer to identify requirements for rehabilitation. The focus was on preventing interruptions to the wastewater treatment plant, minimizing disruptions to university events, limiting impact on Neyland Drive, adhering to budget and schedule, and providing a long-term solution.

The team ruled out the dig-and-replace method due to cost and topside disruptions. Opting for trenchless rehabilitation, we were chosen based on competitive pricing, qualifications, and a unique project approach. Traditional methods like slip lining and cured-in-place pipe (CIPP) were considered but were cost-prohibitive and exceeded the designated area.

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We proposed a unique solution using Warren Environmental’s high build epoxy coating for trenchless pipe rehabilitation. The work was scheduled at night and under live sewer flows. Warren’s epoxy, ideal for wet environments, allowed coating above the water line without bypass pumping. This targeted approach, focusing on the most at-risk area for corrosion, resulted in significant cost and time savings, totaling millions of dollars.

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The choice of Warren’s epoxy was reinforced by its success in a previous KUB project, the Second Creek Trunkline Rehabilitation, which is still in service today six years later. This demonstrated the epoxy's durability in corrosive sewer systems, providing a long-term solution over a temporary fix. The forward-thinking strategy achieved substantial cost savings and minimized disruption, establishing it as an innovative and efficient solution for KUB.

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SCOPE OF WORK

The project’s scope involved rehabilitating 2,349 linear feet of RCP, featuring two segments with varying diameters ranging from 78 to 84 inches. Additionally, the scope included the rehabilitation of seven brick manholes, ranging in depth from 21 to 36 inches, and three concrete vaults.

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The initial phase of the pipe rehabilitation consisted of surface preparation, concrete repairs, and keyway cutting above the water line when the flows were at their lowest point. Subsequently, our crew water blasted to achieve the ideal surface profile for coating application. Using Warren’s 301-14 high-performance epoxy coating, 250 mils were spray-applied seamlessly under live flows. This included the coating of 285 joints and the execution of 877 square feet of spall repairs.

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In parallel, the brick manholes and concrete vaults underwent similar preparation and coating with Warren’s epoxy product. The vaults required strategic staging and protection for KUB’s flowmeter and weir gates. The post-application phase included inspection of the coatings. Adhesion pull tests were conducted, yielding impressive average pipe readings of 1,056 PSI, surpassing the specified requirement of results greater than 300 PSI.

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PROJECT CHALLENGES

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PIPELINE ENVIRONMENT:

Rehabilitating the pipe under live flows posed challenges for our crew, including exposure to hazards like bacteria and debris. Ensuring continuous airflow and weather awareness was crucial due to confined space conditions. We initiated the project with an approved site safety plan, implementing measures such as a safety cable, harness system, and protective gear. Innovative foresight led to a custom device for unconscious crew members. Additional safety measures included a fan system, individual air monitors, and real-time water level and weather monitoring. Despite communication challenges within the pipe, a reliable buddy system was established, reflecting our crew's commitment to a secure working environment amid unique challenges.

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EQUIPMENT:

Warren’s epoxy coating system is delivered through a heated hose from a spray rig on the top side near the access pit. A critical consideration was preventing the heated hose from contacting the water, which could lower the temperature and lead to premature epoxy curing. Our crew used a variety of innovative solutions to bring the hose in and out of the tunnel while keeping it above the waterline to ensure the temperatures did not prematurely drop.

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TRAFFIC CONTROL:

To minimize disruption on Neyland Drive, we collaborated with an engineering consultant to create a custom traffic control plan. The plan, executed at night, featured six setups for each work zone and included setting up and tearing down after every shift, which streamlined tasks to reduce traffic control moves. Identifying areas with overlapping traffic patterns maximized the working area. Our crew optimized efficiency, transitioning from three-hour minimum shifts to 1.5-hour maximum shifts by the end of the project. How the plan was designed and executed maintained limited lane closures at night and zero traffic control during the day.