Investigation of small-diameter steel pipes subjected to axial ground movement

ABSTRACT: Small-diameter steel pipes are often used for distribution of gas to residential homes. These pipelines sometimes run through landslide-prone areas, highlighting a need to better understand their response to ground movements. Many studies were conducted in the past by pulling a pipe through a static soil mass to investigate the behaviour of pipe subjected to axial ground movements. However, in real landslides, a soil mass moves when the pipe can be restrained in the stable ground. It is believed that the effect would be similar to that of pulling a pipe through static soil. A test facility was designed at Memorial University, where a soil mass can move against a pipe restrained on one end, simulating the condition expected during real ground movement. This paper presents the results of a test program completed using the test facility to investigate steel pipes subjected to axial ground movements. Steel pipes of different diameters (26.7 and 60.3 mm) were buried in sandy soil compacted to 96% relative compaction inside a moveable steel tank. Pipes were anchored at one end and free at the other. The tank was pulled at 0.5 mm/min until reaching 35 mm displacement. Varying relaxation times were applied to investigate stress relaxation during ground movements. Pipe axial force, free-end displacement, strain and tank displacement were recorded. Results showed that axial force can be higher during soil pulling than pipe pulling. No reduction of axial force was observed during relaxation. The axial force was found to reduce with repeated cycles of ground movements.