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.