Thinking outside the Circle: Novel Use of Non-Circular Pipe for Dallas’ Shallow Large Interceptor Sewers

Use of non-circular geometry pipe enabled the Dallas Water Utilities (DWU) to overcome the challenges and constraints associated with creating a new larger capacity bypass pipeline through the City of Dallas Glendale Park (Park). In response to a pipe failure in Park, DWU was confronted with having to construct an approximately 2,800 linear foot (LF) bypass alignment to its 54-in. diameter Five Mile Creek Interceptor sewer (Interceptor). Future capacity needs equated to a 72-in. diameter pipeline at the same slope. A traditional circular pipe design approach could not be applied as approximately 41% of the chosen alignment path for a 72-in. diameter pipe would provide less than 1 ft of cover and in one location, the pipe would be above grade. Subsequent analysis of potentially splitting the flow into two smaller parallel circular pipes was not able to identify a combination of parallel configurations that would meet the flow capacity requirements. With this project as a case study, this presentation will examine the novel sewer design and construction of direct-bury non-circular pipe geometries. Utility owners will learn key factors to consider when selecting non-circular pipe geometries, including the benefits, challenges, and limitations. The presenters will also discuss the production aspects and construction handling and quality control methods used for the first direct-bury application of US manufactured non-circular glass fiber reinforced polymer (GFRP) pipe and bifurcation wyes in new wastewater pipeline construction in Texas.