Axial ground movement effects on buried small-diameter MDPE pipes

Abstract

The widespread use of medium-density polyethylene (MDPE) pipelines for natural gas distribution across North America necessitates a robust understanding of soil-pipeline interaction mechanisms, particularly under conditions of ground movement caused by geohazards like landslides. This thesis investigates the axial soil-pipeline interactions in MDPE pipelines using full-scale testing and three-dimensional finite element modelling (FEM). The research addresses critical knowledge gaps in how varying backfill compaction methods, soil densities, and displacement rates affect axial forces and pipe strains, offering insights for enhancing pipeline resilience in geohazard-prone environments. Fifteen full-scale tests were conducted on 42.2 mm and 60.3 mm diameter MDPE pipes embedded at two depths and subjected to controlled axial displacements of soil. These tests were performed at varying soil displacement rates and using different backfill compaction techniques (vibratory plate compactor, hand tamper and no compaction). The influence of compaction on pipe forces was significant with the highest forces for vibratory compaction, while the displacement rate showed only minor effects. The findings underscore a gradual mobilization of axial strain from the anchored end toward the free end of the pipe as soil displaces axially, indicating the progressive mobilization of shearing resistance along the pipe length. Existing ALA (2005) and PRCI (2017) guidelines underpredicted peak force for pipes in dense sands. Threedimensional FEM simulations were used to explore the mechanism of soil-pipe interaction involved during axial ground movements. While the FEM models captured peak forces effectively, limitations were observed in pre-peak and post-peak behaviour, suggesting the need for further refinement. The study emphasizes the significant role of compaction methods and soil parameters in governing pipeline response to ground movement. The findings contribute essential data for refining pipeline design guidelines and improving infrastructure resilience against geohazardinduced soil movements.