Laboratory evaluation of buried high-density polyethylene pipes subjected to localized ground subsidence

The serviceability loss of buried high-density polyethylene (HDPE) double-wall corrugated pipes caused by localized ground subsidence has been reported all over the world. Beam-on-nonlinear spring model is widely used to analyze the structural responses of buried pipes to the localized ground subsidence underneath the pipe. However, the pipe-soil separation is not considered by the beam-on-nonlinear spring model which assumes bonded interaction between the pipe and soil. This is because the spring stiffness could not be assigned as zero. The bonded interaction between pipe and soil is not able to capture the pipe behavior and characteristics of load distribution around the pipe when pipe-soil separation occurs. This study presents a series of large-scale model tests aiming to investigate the performance of buried HDPE double-wall corrugated pipes subjected to the localized ground subsidence. Movable plates installed at the bottom of the model test box are lowered down to simulate the localized ground subsidence. Earth pressures, pipe vertical displacements, and settlements at the backfill surface are monitored. For comparison purpose, free field condition (i.e., without pipe) is also tested. The test results demonstrate that soil settlement troughs above buried pipes are shallower and wider than those at the same elevation in the free field condition. Earth pressures at the top of the pipe are found to increase due to the negative soil arching, i.e., earth pressure is greater than the overburden pressure. It is suggested that three-dimensional soil arching, i.e., soil arching effects in both the transverse and longitudinal directions of the tested pipe, should be considered in calculating the earth pressures at the pipe top. The pipe-soil separation is substantiated by the observation that earth pressure measured at the bottom of the pipe is zero. Finally, empirical equations are proposed to correlate the volume of pipe displacement profile with the volume of settlement trough at the backfill surface to facilitate evaluation of the performance of the pipes subjected to the localized land subsidence