Adaptation of the van Genuchten expression to the effects of temperature and density for compacted bentonites

The main objective of this work is to highlight the influence of variables like temperature and porosity (dry density) on the water retention curve of expansive clays for the analysis of thermo-hydro-mechanical coupled processes (THM problem). The paper presents retention curves of MX-80 bentonite measured under isochoric conditions for different dry densities and temperatures. The influence of dry density on the water retention capacity depends on the suction range, the limiting value being around 30 MPa. For suctions above this threshold value, the retention capacity in terms of water content is higher as the dry density increases, whereas for lower suctions, the lower the dry density the higher the water content for a particular suction. The retention capacity decreases with temperature, more than predicted by the change in interfacial tension of air-water, especially for high temperatures and low suctions. Accordingly, some modifications of the van Genuchten [van Genuchten, M.Th., 1980. A closed-form equation for predicting the hydraulic conductivity of unsaturated soils. Soil Sci. Soc. Am. J., 44, 892-898.] law have been proposed to fit the experimental values. Effects of temperature and porosity on the water retention capacity (other than the traditionally included in the air entry value coefficient) were incorporated through empirical laws that resemble the experimental evidences. By a fitting process, values of the coefficients in those laws were determined for the material used in this work. Finally, several 1D THM simulations using the computer code "CODE_BRIGHT" have been performed in order to analyse the consequences of considering or not temperature and density influences on the water retention curve.