APPARATUS FOR THE RAPID AUTOMATED MEASUREMENT OF UNSATURATED SOIL TRANSPORT-PROPERTIES

To describe the flow of water in unsaturated soils, the constitutive r elationships of capillary pressure and relative permeability are neces sary. To measure these relationships using traditional methods may req uire different experimental apparatuses and can be time-consuming, par ticularly for multiple drainage and imbibition relationships for syste ms containing surfactants at various concentrations. Thus a critical n eed exists for an apparatus that can make rapid measurements. This pap er outlines the design of an automated apparatus that can produce both capillary pressure and relative permeability relationships simultaneo usly and rapidly. The rapidity of the measurements is based on the use of a thin soil sample, a highly conductive capillary barrier, and str ipper tensiometers. The capillary pressure is changed externally, with the change within the sample monitored through the use of tensiometer s. Saturation is determined by monitoring the cumulative effluent, wit h the accuracy of the mass balance enhanced through the active removal of air bubbles from beneath the capillary barrier. A comparison of ca pillary pressure relationships for a fine-grained sandy porous medium produced with this apparatus with those produced with a Tempe cell sho ws that this apparatus yields comparable measurements in about 2% of t he time. Thus the burden of making multiple transport property measure ments can be reduced considerably through the use of this apparatus.