Buried high-density polyethylene pipe deflections at elevated temperatures

The impact of elevated temperatures on high-density polyethylene (HDPE) pipe deflections when deeply buried is examined. Measurements of pipe deflection from full-scale physical tests are reported where 100-mm-diameter, DR 11, HDPE pipes backfilled with sand were subjected to a vertical pressure of 500 kPa for 1000 h while at temperatures of 22, 55 and 80 °C. Short-term vertical deflections were found to increase by a factor of 1.3 when the temperature was increased from 22 to 80 °C as increased temperatures resulted in greater circumferential compression of the pipe. Vertical pipe deflections continued to increase at a slow rate when the pressure was sustained for 1000 h, to values that were 1.4 to 1.2 times larger than the short-term deflections at temperatures of 22–80 °C, respectively. Even under elevated temperatures, it appears that ultimately HDPE pipe deflections are governed by the soil as, when extrapolated to 50 years, vertical deflections of −3.2% of the original mean pipe diameter were predicted at 22, 55 and 80 °C.