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

Abstract

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 multi-phase thermo-hydraulic phenomenon that includes liquid water, vapour, and heat fluxes. It is generally modelled considering unsaturated soils’ thermal energy and water mass balance equations. This paper presents a numerical model to reproduce evaporation processes under controlled environmental conditions. The model was implemented in Comsol Multiphysics Finite Element software and first validated against experimental data from the literature. Then it was used to investigate the role of the 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 the hydraulic conductivity and the retention properties. Hydraulic conductivity mainly impacts the shape of the water content isochrones: fast drying of the superficial layers and slow desaturation of deeper layers occur for 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.