Time-Dependent Field Performance of Steel-Reinforced High-Density Polyethylene Pipes in Soil

Steel-reinforced high-density polyethylene (SRHDPE) pipe was developed to overcome the disadvantages of steel and high-density polyethylene (HDPE) pipes. In consideration of the long-term serviceability of buried pipes, the time-dependent performance of SRHDPE pipes deserves investigation. In this study, three 8-m (26.2-ft) SRHDPE pipes were installed in a trench in the field with a soil cover thickness of 0.9 m (3 ft). The backfill materials were well-graded aggregate base 3 (AB3) aggregate and poorly-graded crushed stone. A new concept, equivalent pipe stiffness factor, was proposed to consider the large difference in stiffness between pipe and soil for calculating pipe deflection under long-term conditions. The test sections were instrumented with earth pressure cells, displacement transducers, and strain gauges and monitored continuously for 680 days. Measured data indicated that earth pressures increased with time in both AB3 aggregate and crushed stone sections. Vertical arching factor (VAF) increased faster in the crushed stone section than that in the AB3 aggregate section. Pipe deflections in both sections increased with time. The maximum pipe deflections in the AB3 aggregate and crushed stone sections were 0.3% and 0.4% of the pipe diameter at 680 days after installation, respectively. Strains of plastic valley, plastic cover, and steel ribs in both sections were all smaller than the AASHTO limit within 680 days. Finally, empirical relationships were developed for the VAF and the equivalent pipe stiffness factor in order to predict the performance of SRHDPE pipes at a given time.