Lateral ground movement effects near connection of medium density polyethylene gas distribution pipes

Abstract

Buried medium-density polyethylene (MDPE) pipes are extensively used for gas distribution systems. These pipes are sometimes exposed to geotechnical hazards such as ground movement, which may cause significant damage to the pipes. Understanding the behaviour of the pipes subjected to the ground movement is critical for transporting natural gas safely and economically using these pipings. This thesis presents an investigation of MDPE gas distribution pipes subjected to lateral ground movements near a connection. Gas distribution systems include a number of connections and lateral branches to supply gas to communities. When a pipe is subjected to the load from the lateral ground movement, the branch pipes experience axial force, and the pipe itself experiences bending deformation. As a result, excessive strains can develop on the pipes, leading to leakage or breakage. In this study, the bending strain on the pipes and the axial force on branch pipes are investigated using full-scale testing. Tests were conducted using 42.2-mm and 60-mm diameter MDPE pipes buried in the ground in a full-scale test facility. Each type of pipe was tested at two different burial depths in dense sand and loose sand. Test results showed that the axial force on the lateral branch depends on the burial depth, the pipe diameter, and soil density. The pipe under lateral ground movement experienced significant bending strain near the connection. The measured responses of the pipes were reasonably estimated within the linear range of deformations using beam-on-elastic spring idealization. For large deformations, elastoplastic spring parameters were required to simulate the pipe behaviour. The bilinear elastoplastic spring parameters recommended in the pipe design guidelines for steel pipes were modified to simulate the measured responses for the MDPE pipes. Based on the validated spring parameters, a parametric study was conducted using a python script to investigate the effect of burial depth, soil density and landslide magnitude on the pulling force and the bending strain.