Response of small-diameter buried steel pipes to horizontal oblique ground movements

The widely utilization of small diameter steel pipeline for energy distribution across Canada, facilitates the importance of understanding the pipe responses due to relative displacement between pipe and surrounding soil during large ground deformation such as landslides. Traditionally, pipe loads induced by ground movement have been investigated by pulling a pipe through stationary soil to generate relative displacements. Most existing studies focus on soil reactions under individual loading modes, including vertical-uplift, horizontal-lateral, longitudinal-axial, and vertical-bearing movements. This research aims to investigate the coupled responses of small-diameter steel pipelines subjected to horizontal oblique (combined axial–lateral) ground movement. For this purpose, the testing facility at Memorial University of Newfoundland (MUN) was modified so that a soil tank (representing the ground) could move against a stationary pipeline segment. The pipe was buried horizontally within the moving soil box, with its axis inclined relative to the direction of ground displacement to simulate realistic landslide-induced loading conditions. The influence of pipe inclination was examined using three steel pipe diameters (114.3 mm, 60.3 mm, and 26.7 mm) and three corresponding oblique angles (80°, 70°, and 60°) relative to pure lateral loading (90°). The backfill soils were placed in layers, with each layer compacted using a vibratory plate compactor to achieve the targeted soil density. The pipe segment was instrumented installing the Fibre Optic Sensor (FOS) at both the front (passive) and rear (active) sides of the pipe at the springline level of the pipe to measure the wall strain. To investigate the effect of horizontal oblique ground movement, the soil forces, pipe wall strains, pipe deflection, soil failure mechanism and tank displacement were recorded during the tests. The findings indicate that the soil forces, pipe wall strain and soil failure mechanism during oblique soil movement may vary with the inclination of the pipe axis. The longitudinal strain data implies that the active side of the pipe is subjected to tension, whereas the passive side is in compression, confirming the bending of the pipe segment. The observations also demonstrate that horizontal oblique pipe–soil interaction is inherently three-dimensional, meaning that 2D plane strain idealization is not applicable for small-diameter steel pipelines. Finally, the applicability of existing design guidelines was evaluated by performing beam-on-spring analysis to simulate full-scale laboratory experiments.