Response of flexible pipes buried in sand under multi-directional movement: understanding fault-pipeline interaction

Buried pipelines are an integral part of critical lifeline systems, and span across wide geographic areas to convey fluid products for human use. Due to geohazards, pipelines could be subjected to transverse displacements in different directions, i.e., displacements normal to the pipe axis. However, limited experimental studies have been reported on the response of flexible pipes when subjected to such displacements. In this study, fourteen large-scale multi-directional dragging tests were conducted on polyvinyl chloride (PVC) pipes in dry sand to promote a better understanding of flexible pipe-soil interaction. The soil restraint, midspan deflection, circumferential strain, and longitudinal strain are found to increase with the pipe embedment depth and decrease with the loading angle. It is observed that the design guidelines of ALA (2005) largely overestimate the peak soil restraint on PVC pipes subjected to lateral movement, while the yield displacement for PVC pipes is observed to be much greater than the ALA (2005) recommendation. Also, the calculation method of Nyman (1984) is unable to provide close estimations of peak soil restraint on PVC pipes for different loading angles. A new calculation method is proposed, forming a design chart that can accurately predict the peak soil restraint to different movement directions.