Determination of the Soil-Water Retention Curve and the Hydraulic Conductivity Function Using a Small Centrifuge

An alternative methodology for direct determination of the soil-water retention curve (SWRC) and evaluation the hydraulic conductivity of the unsaturated soil was developed using a commercially available small centrifuge with a swinging type rotor assembly without in-flight instrumentation. The testing procedure consists of spinning up four initially saturated soil specimens until constant water content is achieved for a given angular speed. The soil - suction relationship is determined by relating the respective water content to the suction magnitude induced by the ceramic plate at the specimen's base. The hydraulic conductivity of the unsaturated soil is estimated by dividing the cumulative flow rate measured at each angular speed by the respective hydraulic gradient applied at specimen's middle height. This methodology was applied for evaluating the SWRC of a residual gneissic soil profile using both, undisturbed and remolded soil specimens. The results show good agreement to other well established methodologies such as filter-paper method, porous plate funnel and suction plate extractor. The determined unsaturated hydraulic conductivities magnitudes were compared to the theoretical predicted values given by the Mualem - van Genuchten model (van Genuchten, 1980) indicating good agreement. Overall, it can be concluded that the methodology proposed ensures good agreement in determining the SWRC and the hydraulic conductivity of studied soils.