Influence of soil confinement on local buckling behaviour of buried pipelines

Buried pipelines can be subjected to differential ground movement events. The ground displacement field imposes geotechnical loads on the buried pipeline and may initiate pipeline deformation mechanisms that exceed design acceptance criteria with respect to serviceability requirements or ultimate limit states. The conventional engineering approach to define the mechanical performance of pipelines has been based on combined loading events for in-air boundary conditions. The pipeline/soil interaction and associated load transfer mechanisms that may initiate local buckling modes in buried pipelines are not well understood. Soil confinement may influence the pipeline mechanical behaviour with respect to initiation of local buckling and wrinkling development.;The initiation and progressive development of local wrinkling does not necessarily constitute pipeline rupture. Operational experience and experimental data have shown that the pipeline, under displacement controlled events, has reserve capacity to experience local ovalization and wrinkling deformation without wall thickness rupture and product release. In this research, the behaviour of buried pipelines subject to combined loading (bending and internal pressure) is investigated through a numerical approach. A three-dimensional continuum finite element model, using the commercial software package ABAQUS/Standard, is developed and calibrated based on available full-scale tests data. Parametric analyses are conducted to evaluate the local buckling response of a pipeline subjected to moment loading for in-air and buried conditions. The effect of geotechnical boundary conditions on pipeline deformation mechanisms and the level of conservatism in current codes and standards are examined. A parametric study was conducted for two types of soil, stiff clay and dense sand. The relationship between the parameters, influencing the pipeline local buckling initiation (e.g. diameter, wall thickness, material grade, internal pressure, etc) and certain strain levels is established through Response Surface Methodology (RSM). The new local buckling strain equations are compared with several in-air based criteria. Recommendations to extend the current research and to obtain more in-depth understanding of soil restraint effects on flexural behaviour of a buried pipeline are presented.