The Tennessee Department of Transportation (TDOT) has approved the longitudinal installation of large diameter, corrugated high-density polyethylene (HDPE) pipe for storm water drainage systems.
Approval came after its year-long field test completed in June 2012 that showed no notable defects, deflection or stress on the pipe buried with shallow cover and fill height depth of three to four feet. Since 2007 the TDOT has allowed the pipe to be used for cross drains, transverse median drains and storm drain systems with up to 18 feet of fill height. Previously, longitudinal use was limited, for example, to side drains under driveways.
Under the direction of TDOT and installed by an independent contractor, the on-site test project used two runs of dual-wall, corrugated HDPE pipe that was manufactured to AASHTO M294 standard, “Corrugated Polyethylene Pipe 300 (12 inch) to 1,200 mm (48 inch) Diameter.” The test site used 84 linear feet of 24-inch and 90-linear feet of 36-inch diameter pipe manufactured by Timewell, a member company of the Plastics Pipe Institute (PPI). Installation conformed to TDOT Standards 204.10(b) and 204.11(b), TDOT Standard Drawing D-PB-1, and appropriate notes in the construction documents
The final inspection conducted by TDOT and Timewell engineers followed TDOT and AASHTO criteria, noting that deflection testing was to occur no sooner than 30 days after installation. Due to easy access and the large diameter pipe sizes, direct physical measurements and observations were taken from inside the pipe and at regular intervals across the entire span of each pipe run. Vertical measurements for deflection of the pipe were taken at the beginning and terminus of each pipe run, at each joint, and generally at 10-foot intervals. Additional inspections were geared to observe the condition of the pipe, looking for material distress such as cracks, tears or punctures. The standard length of an installed HDPE pipe section from Timewell is 20 feet, and all joints were examined for integrity.
“According to the inspection report,” stated Tony Radoszewski, PPI’s executive director, “the pipe retained its shape, was on line and grade, without any imperfections, and showed no signs of distress. Any deflections were symmetrical about their corresponding horizontal and vertical axis and well within the allowable five percent maximum – no racking was observed. Each and every joint appeared well-seated.”