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Working Through Challenges, Clay Pipebursting Project Exceeds Expectations
As are many American cities, Phoenix, AZ, is facing the need to make major improvements to its sanitary sewer system.
Rapid population growth, recent mandates from the state environmental quality department and aging portions of infrastructure have resulted in portions of the city's wastewater collection system being near or above capacity.
Because sewer system capacity deficiencies could have a negative impact on the area's economy, the Phoenix Sanitary Sewer Relief and Replacement Program was established to address these and other issues.
One recently completed improvement was a pipebursting project using vitrified clay (VCP) jacking pipe that included replacing 3,938 feet of existing 12 inch VCP with 18 inch VCP, replacing 2,525 feet of 15 inch VCP with 18 inch VCP, and replacing 720 feet of 12 inch VCP with 15 inch VCP. The existing sewer line's capacity had been exceeded due to growth in the service area.
"To our knowledge, this represents the most significant upsizing and maximum drive length ever completed in the United States using the static pull bursting method with replacement segmental pipe," said C.J. Haas, P.E., resident engineer, Project Engineering Consultants Ltd., engineers for the project.
The utility corridor encompassing the existing line was congested with other utilities making open cut construction challenging, Haas added. The existing pipe was bedded in a soft, dry silty sand material and installed in a trench with widths ranging from three to 5 feet, depending on pipe depths which ranged from 10 to 20 feet. Other utilities were adjacent to the pipe.
The goal of planners, Haas continued, was to consider alternatives that would minimize the conventional open cut construction headaches such as impeding traffic, impacting local business and customers, and ultimately provide a solution less costly and disruptive. Trenchless pipebursting was ultimately chosen to upsize capacity deficient pipes without trenching.
"Pipebursting has been used in the Phoenix area in the past," said Haas, "and while clay pipe had been used as replacement pipe years ago, most recent pipebursting jobs were done with pneumatic heads and HDPE pipe. Static bursting is different, and some of the depths on this project were at the edge of what we had experienced."
The use of pipebursting provided a relatively small job site footprint, and Haas said utilizing segmented pipe eliminated the need for a long lay down area on the project site that would be required with welded pipe.