Thermo-hydro-mechanical modeling of artificial ground freezing taking into account the salinity of the saturating fluid

Abstract

The modeling of Artificial Ground Freezing in geotechnical engineering applications has two main objectives, the first is the prediction of the extent of the frozen zone around the cooling sources (Thermo-Hydraulic models) and the second is the prediction of the ground’s deformations and the site stability (Thermo-Hydro-Mechanical models). Reliable predictions require the consideration of unfavorable hydro-geological conditions such as high seepage velocities, ground heterogeneity and saline groundwater that may negatively influence the performance of AGF. The influence of the saturating fluid salinity on the THM behavior of the ground during freezing is the less documented point among the three and is therefore the subject of this paper. To this end, a fully coupled THM model considering the salinity effect has been derived. The formalism is completely thermodynamically consistent and introduces some simplifying assumptions, especially to describe phase change terms (capillary pressure and latent heat), in order to achieve a mathematical formulation that can be easily handled by computation software. Stress-free freezing laboratory tests carried out on specimens initially fully saturated with sodium chloride solutions at three different concentrations allowed to validate the proposed approach and to highlight some key mechanisms associated with the phase change of saline-saturated porous media.