Determining the hydraulic properties of a swelling soil from a transient evaporation experiment

Most methods used to determine the hydraulic properties of swelling soils (i.e., the shrinkage curve, the moisture retention curve, and the hydraulic conductivity curve) are time consuming because they require measurements of several different parameters (either in separate experiments or by using very expensive equipment). We propose a simple evaporation experiment to simultaneously determine all three soil hydraulic properties. The method is illustrated using samples of a vertisol from the Senegal river valley. The value of the shrinkage curve is determined during the experiment by horizontal and vertical linear deformation measurmenets, whereas an inverse parameter estimation method is used to determine the moisture retention curve and the hydraulic conductivity curve. This method relies on a water flow model that takes into account the three-dimensionsl and anisotropic deformation of the soil. The reliability of the estimated parameter values was checked and we compared the results with those obtained by a multistep outflow experiment. Good agreement was found between the results of the different procedures. The sensitivity of the method to deformation was also analyzed. In the soil investigated, the inverse method does not seem to require the use of a water flow model that takes into account deformation. However, a correction for deformation is needed if the characteristic functions are sought in terms of the volumetric water content of the soil. (Résumé d'auteur