A note on falling-head and rising-tail permeability tests on saturated soils in centrifuge

The falling-head and rising-tail method for permeability test allows for both inflow and outflow rates to be conveniently measured. This helps to detect any possible swelling or consolidation of specimen during testing and to identify the continuity of flow of water through the specimen. It has been widely adopted to measure the hydraulic conductivity of saturated porous media of extremely low permeability, such as hydraulic barrier soil materials. Centrifuge permeameter test with this method has recently been devised to accelerate water flow and reduce the time needed for testing. The accompanying equation for calculating hydraulic conductivity is, however, found to be simplified because it was formulated by idealizing such a variable-head test as multiple segmental constant-head tests. In this paper, a new generalized equation is established based strictly on the variable head. Moreover, based on curve matching between the rates of flow into and out of the soil specimen, an approach is also proposed to identify the continuity state of flow. The data relevant to this state are extracted for performing the calculation of hydraulic conductivity. The practical application of the proposed equation and its associated approach is illustrated through a reanalysis of recently published experimental data in the literature.