United States Department of Transportation
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Evaluation and Performance of HDPE Pipes Under CDOT Highways, T-Rex and Other Locations
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2018-03-01
[PDF-154.65 MB]
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TRIS Online Accession Number:01666521
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Edition:FINAL REPORT
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NTL Classification:NTL-HIGHWAY/ROAD TRANSPORTATION-Construction and Maintenance;NTL-HIGHWAY/ROAD TRANSPORTATION-Pavement Management and Performance;
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Abstract:HDPE pipes used in CDOT drainage systems are expected to have a 50-year design life. During the T-Rex project in 2003 a number of HDPE pipes were installed with shallow cover. Later, the majority of these pipes had to be removed and replaced after they were damaged by construction equipment driving over installed pipes, and excavations occurring near installed pipes. In this study, performance of HDPE pipes under CDOT highways was evaluated by: an extensive literature review; field studies utilizing manual inspection, CCTV video inspection, and laser-ring profiling technology; and, by observing a CDOT HDPE pipe installation project. Since CDOT has a limited number of such sites, a literature search was conducted to determine if cities and counties within Colorado or other state DOTs have evaluated the performance of HDPE pipes in climate zones, terrain, and construction-zone conditions similar to those found in Colorado. In general, review of other DOTs’ experiences revealed that most have encountered HDPE performance problems in the form of excess deformation (greater than 5%). That review also has shown that structural integrity of installed HDPE pipelines tested by the DOTs generally is below acceptable levels of serviceability. The review also determined that not adhering to strictly-enforced HDPE pipe-installation procedures was the cause of many of the performance problems. Field inspections carried out for this research project were limited in scope. However, laser-ring profiling of 5 HDPE pipes in 2016 near Colorado Springs confirmed a trend for progression of pipe deformation through time under shallow-cover conditions. After 4 years of operation, 3 of the 5 pipes experienced 5% deflection. HDPE pipe segments observed by CCTV video monitoring along the T-Rex Project site had in excess of 10 feet of cover. These pipes did not show any visible deformations, but they could not be laserring profiled due to the amount of debris in the system. The study recommends that these pipes be cleaned and fully inspected. In Colorado, due to the limited number of HDPE pipe installations which have been in operation for more than 15 years, further laser-ring profiling of pipes is needed to evaluate their long-term performance. In general, it is recommended that all previous monitoring points established on prior research projects be measured and evaluated for long-term hydraulic and structural performance. Studies by Kentucky, Ohio, Missouri, South Carolina transportation departments and others demonstrated the difficulty of achieving problem-free installations of HDPE pipes, and that the pipes do not always perform in accordance with idealized, theoretical results. Significant-to-severe deflection, corrugation “growth,” crown and invert flattening, racking, sagging, and radial cracking have been observed in pipe sections in numerous test cases. Experiences by other DOTs demonstrate that not adhering to strictly-enforced installation procedures was the cause of some performance issues. A typical installation of an HDPE pipeline observed as part of this study showed that standards for trench width, depth, and cover were not being followed. It is recommended that these standards be strictly enforced.
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