United States Department of Transportation
i
Re-Rounding of Deflected Thermoplastic Conduit, Phase 2
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2021-06-01
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[PDF-10.30 MB]
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Edition:Final Report
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Abstract:Re-rounding is a technique for remediating excess deflection in a thermoplastic pipe using a pneumatic device vibrating along the vertical axis and pushing against the inside crown and invert to restore the original pipe shape and redistribute the surrounding backfill. Since the process has not been evaluated on HDPE pipe outside a couple older reports, and the method is routinely used by contractors to remediate deflected thermoplastic pipes, ODOT wanted to evaluate the technology as a lower-cost alternative to removal and reinstallation of deflected pipes. Three 36 in (0.9 m) HDPE pipes were installed in ODOT Structural Backfill Type 1 (Item 304 aggregate), 2 (sand), or 3 (AASHTO #57 aggregate), and two 18 in (0.45 m) pipes were installed in Type 2 and 3 backfill. Pipes were intentionally installed with substantial deflection (10% or more) and then re-rounded by a vendor. The pipe conditions were measured and monitored by collecting profiles, measuring vertical deflections, monitoring soil pressures, soil stiffness, acceleration of soil particles (peak particle velocity), backfill characteristics, and depth of pipe corrugation before and after re-rounding. Re-rounding successfully reduced vertical deflections in all cases, though not always enough to meet the current serviceability criterion. The pipe in Item 304 backfill were the most resistant to re-rounding, going from -13.91% deflection to -8.62% after three passes with the device. The two pipes in Type 2 backfill (sand) responded better after two passes of the device (-9.89% to -8.57% for the 36 in (0.9 m) pipe and -14.50% to - 7.47% for the 18 in (0.45 cm) pipe). Pipes in Type 3 backfill (AASHTO #57 aggregate) were much easier to reround, taking only one pass of the device to go from -10.18% to -2.52% for the 36 in (0.9 m) pipe and -16.67% to -6.17% for the 18 in (0.45 m) pipe. Pressure data were consistent with redistribution of backfill particles, particularly fines.
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