CENTRIFUGAL TECHNIQUES FOR MEASURING SATURATED HYDRAULIC CONDUCTIVITY

Centrifugal force is an alternative to large pressure gradients for the measurement of low values of saturated hydraulic conductivity (K(sat)). With a head of water above a porous medium in a centrifuge bucket, both constant-head and falling-head measurements are practical at forces up to at least 1800 times normal gravity. Darcy's law applied to the known centrifugal potential leads to simple formulas for K(sat) that are analogous to those used in the standard gravity-driven constant- and falling-head methods. Both centrifugal methods were tested on several fine-textured samples of soil and ceramic with K(sat) between about 10(-10) and 10(-9) m/s. The results were compared to falling-head gravity measurements. The comparison shows most measurements agreeing to within 20% for a given sample, much of the variation probably resulting from run-to-run changes in sample structure. The falling-head centrifuge method proved to be especially simple in design and operation and was more accurate than the constant-head method. With modified apparatus, K(sat) measurements less than 10(-10) m/s should be attainable.