POROSITY AND PERMEABILITY IN SEDIMENT MIXTURES

Porosity in sediments that contain a mix of coarser- and finer-grained components varies as a function of the porosity of each component and of the volume fraction of the finer-grained component. We consider model sediment mixtures representing poorly-sorted sands and sandy gravels. An existing fractional packing model for porosity was expanded in order to represent mixtures in which finer grains approach the size of the pores among the pre-mixed coarser grains. The model well represents the porosity measured in experiments in which grain sizes and volume fractions were systematically changed for each component. Permeability values were determined for sediment mixtures using both a method based on grain-size statistics, which incorporates the fractional packing porosity model, and air permeametery methods corrected for the effects of flow in the high Reynolds number regime. Values determined with a water-based constant-head permeameter were taken as a standard for comparison. Permeability values determined by grain-size statistics and by air-based methods, both, corresponded closely to the water-based values.