Permeability Measurement of Granular Porous Materials by a Modified Falling-Head Method

Liquid flows through granular material are common phenomena in different engineering fields. Under certain conditions, this type of flow can be described by Darcy’s law, which involves the permeability of the porous medium. Experimental characterization of this parameter is then of importance to many practical applications. The falling-head permeability test is regarded as one of the most commonly used methods for that purpose. The required manipulations are easy and rapid, which makes it preferable, especially for field tests. However, due to practical difficulties of carrying out such measurements, it is only applicable to porous materials with permeability values lower than ${10}^{-10}{\mathrm{m}}^2$. To enlarge the test range while keeping its advantages, a modified test procedure is proposed here to measure saturated permeability values two orders of magnitude larger, namely around ${10}^{-8}{\mathrm{m}}^2$. Tests were performed on granular beds containing single-diameter and multiple-diameter beads. Experimental results showed that the saturated permeability can be accurately predicted by the revisited Ergun’s equation with its first empirical constant equal to 180. Two important factors must be considered when performing these tests. The first one is the data-processing method to compute the permeability from experimental data: both the gravity and pressure drop of the setup must be taken into account. The second one is the selection of test fluid. By comparing water and silicone oil, it was shown that the viscosity should be adapted depending on the permeability of the sample to ensure consistent and repeatable results.