HYDRAULIC CONDUCTIVITY OF THE MATRIC POROSITY OF AN UNSATURATED VERTISOL - A FIELD AND LABORATORY COMPARISON

In many swelling clay soils several types of porosity can be defined: matric, structural and crack porosities, Measuring the hydraulic condu ctivity associated with the matric porosity is of major interest becau se soil movements are governed by matric water flows. Our purpose was to determine the matric conductivity of a vertisol from Guadeloupe (Fr ench West Indies) under laboratory and field conditions. We used an Eu lerian flow description to measure the conductivity of natural vertiso l clods in the laboratory with a drying method. In order to take into account soil movements in every direction, we introduced a tensorial a nalysis of soil deformations and hydraulic conductivity. The instantan eous profile method was used in the field under wetting conditions. Us ing soil layer thickness transducers we described water flows in a mat erial coordinate system that can deal with volumetric soil deformation s. For wet soil the ratio between the hydraulic conductivity measured in the field and that measured at the laboratory was around 10. Howeve r, because the spatial variation of the water content was large, no fi nal conclusion could be drawn to explain this discrepancy. We showed t hat the gradient of the overburden potential was smaller than that of the matric potential in the field experiment.