Spirally Wound Solution for a Deteriorated Trunk Sewer
In today’s fast-paced and ever-changing world, the underground construction industry must be willing to adapt and consider new technologies to stay competitive and meet the demands of modern-day projects.
Whether incorporating sustainable materials, utilizing advanced design software, or implementing innovative construction methods, being open to new ideas and approaches can help increase efficiency, reduce costs, and improve the overall quality of a project. By embracing new technologies and being flexible, clients and customers can produce projects that not only meet but exceed expectations.
When the Washington Suburban Sanitary Commission (WSSC) searched for a solution to rehabilitate the deteriorating 102-in. Anacostia Trunk Sewer in Laurel, Maryland, it quickly learned that traditional trenchless methods were not an option. The pipe, which runs through a United States Army Corps of Engineers (USACE) levy and Bladensburg Park, was severely deteriorating due to the highly corrosive environment — high levels of hydrogen sulfide (H2S) — with steel exposed throughout its length. Two siphons within the pipe alignment are 96 in. and 102 in., with significant slopes and sharp radii at the bends. The project location also posed several challenges, including the Corps not permitting a cured-in-place pipe (CIPP) method because it would require tankers within their levy as they were concerned about a potential spill. In addition, the pipe needed to remain available for use should the area incur significant weather, eliminating rehabilitation options that would typically put it out of service for days at a time.
Greely and Hansen was hired as the engineering firm to find a solution. After considering all the options, Greely and Hansen recommended that spiral wound rehabilitation (SPR) would resolve all the pipe and location challenges. The SPR profile provides corrosion resistance when subjected to hydrogen sulfide H2S, its installation can be done in low flow situations, and it offers a flexible profile capable of navigating horizontal/vertical bends, curves, and offsets. Of particular interest to WSSC was the fact that the SPR method can be started and stopped at any point in the process. Unlike other rehab methods, SPR is ideal for unexpected rain events and can eliminate the need for a costly wet weather event bypass system that typically isn’t used. The unique feature combination ultimately led WSSC to select SPR for the project, and the winning bidder for installation was SAK Construction.
SPR is the modern solution to consider for rehabilitation needs where access is difficult, odd shapes and curves exist, corrosion resistance is needed, and work must be done in live flow conditions. Like CIPP, SPR does not require extensive excavation or other disruptive work and can be installed via any manhole found across the country. This makes it a convenient solution for pipelines located in difficult-to-reach or densely populated areas. The material used for the spiral wound rehabilitation will vary depending on the type of pipeline being repaired, as well as the specific requirements of the repair.
Profile selection correlates back to the pipe’s required stiffness factor and diameter, but there are options for most needs and applications. SPR can also conform to odd pipe shapes and curves. Installation can often occur in low live flow situations, which reduces the capacity needs of bypass to accommodate wet weather events. Despite the slight reduction in cross-sectional area (i.e., pipe diameter), the reduced Manning’s Coefficient (used in Manning’s equation to calculate flow in open channels) in the repaired pipe typically leads to an increase in the rate of flow. Lastly, it is a relatively low-impact solution as the process does not involve extensive excavation, and the materials used are environmentally friendly.
For the Anacostia Trunk Sewer, SAK installed SPR specifically designed to provide a fully structural and corrosion-resistant liner within the host pipe (PVC with steel reinforcement). While it was technically capable of the task, SPR had yet to be used on siphons in the past, and SAK needed to figure out the details of how to execute it. The biggest challenge was addressing the 102-in. siphons, with slopes of 23 and 27 degrees, respectively. Specifically, these pipelines had exceptionally sharp radii at the bends, which SPR had never attempted before, and which would push the machine to its limits. These bends created small joints between the straight and diagonal runs that required an innovative solution.
SAK developed a unique solution — the horizontals and diagonals were wound with SPR. The resulting joints were filled with a geopolymer and then finished with a carbon fiber reinforced polymer (CFRP) layup to connect the sections. The result was a smooth transition with continuous structural integrity throughout the pipe. Once the pipe was wound with SPR, the annular space was filled with a low-weight cellular grout to complete the lining system. A new structural and corrosion-resistant pipe was completed.
“As a leading innovator in the pipeline rehabilitation industry, we are thrilled to have successfully met the challenges of the Anacostia Trunk Sewer project and demonstrated the benefits of SPR,” stated SAK senior project manager Kenneth Sprau. “Our team of experts and field technicians worked diligently to ensure a seamless and efficient installation, resulting in a pipeline infrastructure that is now stronger and more resilient than ever before. We understood the importance of solving this complicated rehab task and are proud to have played a part in WSSC’s success. We are committed to providing exceptional services to our clients and finding new methods of addressing their operation needs.”
In conclusion, mechanically spiral wound rehabilitation is a rehabilitation technology that is highly effective for repairing and reinforcing existing pipelines with challenging structural requirements. It offers a cost-effective solution that can save time and money compared to traditional pipeline replacement methods.
Additionally, it is a versatile solution that can be used in various types of pipelines, making it an alternative for many industries considering dig and replace. The process is relatively quick and easy and can be without extensive excavation or other disruptive work. Furthermore, it is a low-impact solution that minimizes environmental impact. Overall, spiral wound rehabilitation is a reliable and efficient option for maintaining and extending the lifespan of pipelines.
Jim Kalishman is the chief information officer at SAK Construction LLC.