Frost heave model of canal considering influence of moisture migration and phase transformation on temperature field

Abstract: The great latent heat of the water transfer and phase transformation in the winter has a significant effect on the temperature field of the canal base soil. The researches on the freezing-thawing of frozen soil with moisture phase change are mostly based on the road foundation, buried pipe, and so on. The study on frost heave damage of lining canal is relatively less. As the canal is in water-carrying condition for a long time, the moisture content of canal foundation soil is high, especially in excavation canal because of the high groundwater table caused by moisture convergence. Under the preceding special geological conditions, as the canal foundation soil is freezing, not only is the water frozen in situ, but also the unfrozen water migrates to the freezing front and changes phase, and then the temperature field and displacement field in canal foundation are influenced by reason of tremendous latent heat of phase change. Although in some past thermal-mechanics coupling calculations the latent heat of moisture phase change is in consideration, the source of moisture with phase change is not completely considered, the computed results of temperature field are not precise enough, and the inaccuracy of the results can lead to the error of frost heave deformation calculated by thermal-mechanics coupling models. So the article established a frost heave model for canal foundation frozen soil, and the water migration and phase change were taken into account in this model. The model regarded the permafrost as cryogenic expansion material, in which the latent heat was added to the conduction equation, and the latent heat is equivalent heat capacity. According to Clapeyron equation and Darcy's law, the article established the expression of moisture migration of freezing fronts in saturated freezing soil, and the latent heat of moisture migration was as the source term of conduction equation. In order to verify the reasonableness of the model, the COMSOL was used, which is a kind of large-scale software for multi-physics fields coupling for numerical calculation. Results showed that in the temperature and displacement field the phase change produced a great influence. After considering the phase change, the freezing depth of the soil advanced slowly, the maximum frozen depth was 1.5 m, and it was near to the actual value which was 1.8 m. But if the moisture phase change was not in consideration, the calculation value of maximum frozen depth was 3 m, and it was much greater than the actual value. As the moisture phase change was in consideration, the maximum normal displacements on the shady slope, sunny slop and canal bottom were 9.65, 4.81 and 2.0 cm, respectively. Compared with the model not considering phase change, the frost heave model proposed in this article is more in line with the actual situation. So in order to make the calculation results accord well with actual value, the influence of moisture phase change on temperature fields and displacement fields can't be neglected. The present results can provide reference to engineering design for frost heave resistance in cold region.