| Soil expansion during freezing is caused by soil water freezing and moisture migration from unfrozen to frozen soil. This process results in frost heaving, and it may cause damage to structures built in the permafrost or seasonally frozen ground. The understanding and simulating of soil freezing process has been a long-term goal of much research in cold regions engineering.;In this thesis, a conceptual model for calculating the amount of heaving and the resulting stresses in a freezing soil, on the basis of three coupled field: heat transfer, moisture migration and stress, is presented. This model takes into account the non-homogeneity of the frozen zone due to temperature variation, as well as the effects of frozen soil creep on stress distribution. In this model, the Clapeyron equation is used to determine the liquid water pressure and to describe the effect of stress field on the heat and moisture transfer within the freezing fringe, while the associated flow rule is used to define creep strains in frozen soil.;This model was used to simulate a test on a saturated cylindrical sample of silt under 50 kPa in unidirectional open freezing system was first carried out. The predicted temperature field and the amount of heave are in a good agreement with the experimental results published by Penner (1986). However, in addition, the simulation furnished also the complete stress field during freezing, which made it possible to take into account the effect of external loading on the amount of frost heave.;Secondly, the proposed model was used to simulate ground-pipeline interaction for a chilled pipeline experiment carried out at the pipeline test facility in Caen, France. The simulated temperature profile agrees well with the measurements, and predicted stresses acting against the pipeline seem to be of a correct order of magnitude. Because of a lack of exact information on the axial confining conditions of the pipe, it was decided to solve first two extreme pipe-confinement cases, i.e., the case of a free floating pipe and the case of a rigidly fixed pipe. It was considered that real conditions would be located between these two limiting cases. To test this assumption, and in order to take into account the possible resistance due to the longitudinal confinement of the pipe, another possible pipe confinement condition was also considered, in which the pipe resistance was represented by a virtual spring. The simulated frost heaving under this pipe confinement condition was directly controlled by the assumed spring stiffness, and was found to be always located between those of the two limiting cases. |
