Shaping Tomorrow’s Pipes Today: CIPP Lining of Elliptical HDPE in Omaha

Abstract

The 6th and Leavenworth Grit Facility effluent sewer is a 40” diameter HDPE pipe constructed in 1977 that traverses 820 feet from the grit facility to a diversion structure near the banks of the Missouri River in Omaha, NE, see Figure 1. As part of a larger grit facility project, inspections of the effluent sewer were performed to evaluate the structural integrity of the pipe and identify necessary improvements. Inspections identified multiple defects including broken, buckling pipe in the invert and an ovality in some locations as much as 20%. The pipe makes multiple 90-degree bends, travels below many utilities, and runs adjacent to a large electrical substation, making open cut construction virtually impossible. To identify potential solutions to rehabilitate the pipe through trenchless technologies, the City of Omaha Public Works obtained Lidar scanning to properly assess the actual pipe shape. Scanning indicated that because of the significant ovality, in some locations the pipe was actually 28.8” tall by 43.2” wide. A variety of alternatives were evaluated to develop a cost-effective solution. Although the pipe makes multiple 90-degree bends and has limited upstream and downstream access due to the grit facility and diversion structure, respectively, a trenchless solution was preferred. This paper will discuss field investigations performed, alternatives evaluated, cured-in-place pipe (CIPP) lining design calculations for an elliptical shaped pipe, rehabilitation work including installation of new manholes, spot replacement of sewer pipe, including challenges associated with connecting new round pipe with deformed existing pipe, and lining through multiple 90-degree bends, which was completed in 2024.