Permafrost thaw induced settlement is a major concern for pipeline design and operation in the Arctic region. For a buried warm pipeline in permafrost, heat losses can thaw the frozen water in the surrounding soil and create a thaw bulb around the pipeline. The underlying soil will then settle and consequently cause settlement of the supported pipeline. Uneven settlement along the pipeline will induce pipeline bending, and may even damage pipeline during operation if resulting strains exceed allowable values. Using finite element analyses to predict pipeline behavior due to permafrost thaw induced settlement can provide guidance on pipeline engineering considerations such as pipeline design, installation and mitigation.

The authors previously presented a finite element model (FEM) developed to study the thaw induced settlement and stresses in pipeline by sequentially coupling a 2D heat transfer model and a 3D soil consolidation/soil-pipe interaction model. The heat transfer and thaw settlement were validated by comparing the numerical output with respective analytical solutions. As a continuation of the FEM development, a three-dimensional (3D) fully coupled model to simulate heat transfer and soil consolidation is developed in this paper. This model solves all field equations simultaneously, including temperature, pore pressure and displacement variables. Heat transfer process can be continuously updated as soil consolidation and pipeline settlement occur. Conclusively, the 3D fully coupled model can capture the transient behaviour and interaction between heat transfer, soil consolidation, and pipeline deformation, and simulate the involved mechanisms more realistically. The 3D fully coupled model is compared with the verified sequentially coupled model.

Thermosyphons are then implemented into the fully coupled model to mitigate thaw induced settlement. The effects of thermosyphons on thaw bulb growth around warm pipe and thaw induced pipe settlement are studied.

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