The role of hydraulic and thermal properties of soil in evaporation: a numerical insight

Evaporation from geological formations results from the interaction between the geomaterial and the atmosphere. Geotechnical engineering issues, such as slope stability, pollution containment and soil heave/shrinkage, require a deep understanding of the soil–atmosphere interaction ruled by evaporation. Evaporation is a multiphase thermo-hydraulic phenomenon that includes liquid water, vapour and heat fluxes. It is generally modelled considering the thermal energy and water mass balance equations of unsaturated soils. This paper presents a numerical model for reproducing evaporation processes under controlled environmental conditions. The model was implemented in the Comsol Multiphysics finite-element software and first validated against experimental data from the literature. Then, it was used to investigate the role of hydraulic and thermal properties in the evaporative response. The numerical results revealed differences in the evolution of the water content profiles over time due to the interplay between hydraulic conductivity and retention properties. Hydraulic conductivity mainly impacts the shape of water content isochrones: fast drying of superficial layers and slow desaturation of deeper layers occur with decreasing hydraulic conductivity values. On the other hand, the moisture capacity primarily impacts the thickness of the desaturating layer, which decreases for higher values of the moisture capacity.