Loading-unloading-reloading responses of MDPE pipes in sand subjected to axial ground movement

ABSTRACT: Medium-density polyethylene (MDPE) pipes are one of the common means of gas distribution in Canada and worldwide. These pipes are sometimes exposed to ground displacements caused by landslides and other geohazards. Pipelines can be subjected to load-unload-reload cycles in areas where landslides occur in succession. Repeated loading-unloading-reloading on buried MDPE pipes can affect behavior at the pipe–soil interface and the corresponding pipeline responses. However, very limited study is currently available on the behavior of pipes subjected to loading-unloading-reloading due to landslide. This paper presents a study on the loading-unloading and reloading behavior of MDPE pipes under axial ground movement. A full-scale laboratory facility developed at the Memorial University of Newfoundland was used in the tests. The facility was designed to simulate the axial ground movement where a soil box is moved over two rails. During testing, the pipe was instrumented with fiber optic strain sensor along the entire length to monitor axial strain. A significant drop in axial soil resistance was observed after the first cycle, indicating the damage of soil–pipe interface bonding. Pipe wall strains gradually decrease from the fixed end of the pipe to the free end along the length.