Experimental and theoretical study of mechanical deformation of freezing saturated soil

An intensive development of infrastructure in the far North and application of the artificial ground freezing technology for construction of civil and industrial buildings require an accurate description of frost heave caused by freezing of pore water in soils. It is important to understand this processes at the developing stage for the aim of safety exploitation of constructions. The present work is devoted to an experimental and theoretical study of the frost heave in laboratory samples of water saturated sand. Artificial freezing of the sample is performed in a chest freezer. During freezing measurements of temperature and strain are carried out by a control system consisting of a set of thermocouples and fiber optic sensors based on Bragg gratings. To analyze the obtained experimental data, a thermo-hydro-mechanical model has been developed. Water saturated soil is supposed to be three phase porous media consisting of a drained skeleton, water and ice. The model includes the energy conservation equation, the mass balance equations for moisture and ice content, the equilibrium equation and the constitutive relations taking into account an influence of the phase transition of water on heat and mass transfer and the additional volumetric strain. The numerical solution of the nonlinear partial differential equations of the model is performed by the finite element method. The feature of the model is a possibility to take into account the crystallization kinetics on the frost heave of the freezing saturated soil. As a result of the study, a good qualitative and quantitative agreement between a temperature measurement in the volume of the sample and the results of the simulation has been obtained. A comparison of the fiber-optic sensors readings with the results of the numerical simulation has shown that the calculated values are slightly deviated from the experimental ones. On the basis of the measurements analysis and the numerical results it can be concluded that the frost heave proceeds in a long time after the phase transition starts within the temperature range below the temperature of water freezing.