Effect of the clay-water interaction in the hydration of compacted bentonite used in engineered barriers

Compacted expansive clays are considered in the design of barriers for different engineering applications. The expansion and sealing capacity of those clays when hydrated is the main engineering property in that particular context. Numerical models used to analyse and predict the behaviour of these barriers need, among other constitutive laws, the soil water retention curve. In general, numerical codes used in those calculations are formulated considering the degree of saturation as the variable to indicate the water content within the porous medium. Because of that, it is common to express the water retention capacity as a relation between the suction and the degree of saturation. Surprisingly, degrees of saturation larger than one are systematically obtained in the laboratory at low suction values in the case of samples of expansive clay tested at constant volume. This effect is attributed to the density assigned to the water within the pores, which is assumed equal to that of the bulk water. In a previous work a method which defines the density of water in samples of expansive clays as a function of the suction was developed. Using this relation, water retention curves where the degrees of saturation are lower than one are obtained. This work compares experimental results of the hydration processes of a compacted sample of expansive clay with those obtained in numerical models where different laws for the water density were considered. Conclusions with respect to the hydration time as well as to the quantity of water needed to saturate the sample are obtained.