Laboratory Investigation of Buried Small-Diameter Steel Pipes Subjected to Axial Ground Movement

Abstract

Small-diameter steel pipes are often used for the distribution of gas to residential homes. These pipelines must service the end-user, even in landslide-prone areas, necessitating the study of their response to ground movements. Many studies were conducted by pulling large-diameter transmission pipes through static soil mass to investigate the behavior of pipes subjected to axial ground movements. The effects of soil movement around a restrained pipe in the field are believed to be similar to that of pulling a pipe through static soil. A test facility was designed at the Memorial University of Newfoundland, where a soil mass was pulled around a buried pipe fixed at one end, simulating the condition expected during ground movement. This paper investigates the axial resistance of steel pipes with varying diameters (26.7, 60.3, and 114.3 mm) in dense sand using the test facility. The tank was pulled for multiple pulling phases and held in place for varying times between each pull to investigate stress relaxation during ground movements. Pipes were instrumented with distributed fiber-optic sensors to capture the development of strains along the pipe. Results showed that the normalized axial force was higher during soil pulling than pipe pulling. No reduction of axial force was observed during the relaxation period. Measurements of axial strains along the length of the pipe indicated negligible pipe elongations during testing. The outcomes of this research are applicable to the integrity assessment of small-diameter steel pipes in areas prone to ground movements. Ground movements can impose additional stresses and strains on pipes in a distribution network, necessitating evaluation for fitness-for-service assessment. This paper presents an assessment of pipe responses under axial soil loading in an intermittent soil movement cycle. The insights gained from this research will be useful for assessing pipes in the field under similar ground movement scenarios.