Performance assessment of buried pipelines considering soil-structure interaction

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Buried pipelines are widely used as an economic means of transporting liquid and gas. Pipeline failure occurs every year in Canada and worldwide resulting in significant economic and environmental consequences. Factors contributing to pipeline failure include local defects resulting from manufacturer imperfection, dents during construction/operation, and corrosion; and operational/environmental loads. Structural failure of the pipe often initiates locally and propagates gradually or catastrophically, depending upon crack propagation behaviour, through interaction with surrounding soil. This research investigates soil-pipe interaction for the assessments of the structural failure initiation and propagation in a pipe wall due to local defects and the ground loads on pipelines, for municipal cast iron water mains and steel energy pipelines, respectively. For structural failure assessment, finite element modeling techniques will be developed to model crack propagation in the pipe wall using fracture mechanics. The point of initiation of a crack will be defined by creating small defects of different shapes on the pipe and/or by increasing stress concentration locally using a void in the backfill and/or applying concentrated forces simulating sharp objects (rock pieces) in the bedding. Pipe material properties (i.e., elastic parameters, strain-rate dependent stress-strain relations and fracture toughness) for the analysis will be determined using laboratory tests with specimens extracted from pipe samples. For modeling the ground load during axial pullout, finite element modeling will be performed with simulation of large deformation and strain localizations in the soil surrounding the pipeline. The stressstrain behaviour of soil will be modeled through development of new constitutive models capturing the pre-peak hardening, post-peak softening, relative density and confining pressure dependent behaviour of sand. For the constitutive model development, laboratory tests will be conducted with particular attention to the soil behaviour at a low stress level, because the stress around the pipelines is generally lower than the expected stress in typical geotechnical problems. The understanding of the failure mechanisms and the loads from this research can be used to develop novel design guidelines for the pipelines. Outcomes of this research will thus contribute towards rational design of municipal and energy pipelines and thus to the minimization of pipeline failure. Two doctoral, three Masters and two undergraduate students will be supported through the proposed NSERC Discovery grant.