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Frost heave and thaw settlement are two critical factors that need to be considered in the design of chilled gas pipelines in cold regions. Due to the variation in seasonal temperature and operating conditions (e.g., pressure and temperature at the compressor stations), the pipeline temperature in some segments might vary from subzero to above-zero during winter and summer. This study examines the freezing and thawing for cyclic and constant temperatures at the pipeline and ground surfaces based on the response of fourteen model pipes tested in a geotechnical centrifuge. The cyclic (temperature) operation reduces the frost heave rate per year and causes net settlement in some cases. When the thaw bulb resulting from an above-zero operating temperature is less than the previously developed frost bulb, upward water flow occurs through the thawed soil, which could alter the pipeline–soil interaction behaviour. Five types of freeze-thaw-induced vertical displacement of the pipe have been identified from the centrifuge test results.

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The objective of this paper is document numerical and physical modelling carried out under the SIIBED program in order to develop, calibrate and validate a design tool for assessment of risk to subsea infrastructure due to ice keel interaction with pipelines, flexible flowlines, and electrical cables. Soil response is a key factor in the complex interaction between surface-laid flowlines, iceberg keels, and the seabed. In this study, centrifuge model tests and accompanying large-deformation finite element analyses were performed to investigate the soil behavior under various water depths and pipe–soil interaction rates. A series of centrifuge tests were completed using a scaled model of a 0.324 m diameter pipe in dense silica sand with a viscous pore fluid. The model pipe was pushed into the model seabed at a 60° penetration angle, at various penetration rates and water depths. The prototype-scale pipe–soil interaction problem was modeled using the Coupled Eulerian–Lagrangian method. Effective stress based dense sand constitutive behaviors were simulated using a modified Mohr-Coulomb model. The pipe–soil interaction was tested under backpressure and with loading speeds comparable to mean iceberg drift speeds. A significant increase in soil resistance was observed between slow and rapid penetration tests and between the drained and undrained CEL models, indicating that penetration rate and drainage condition can greatly affect soil resistance. Furthermore, a partially drained CEL model was developed to illustrate the connection between penetration rate and drainage condition qualitatively, and how they affect the soil resistance. Meanwhile, the soil response was not sensitive to the water depths (or backpressures) in the centrifuge tests, while a high sensitivity was shown in the undrained CEL model. Potential reasons are explored.

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