Grain size distribution and its effect on the permeability of unconsolidated sands

Since permeability is the measure of the ease with which water moves through aquifer material, certain relationships must exist between permeability and the statistical parameters that describe the grain size distribution of the porous mediums. Experimental studies to investigate these relationships consisted of systematic variation of the values of the statistical parameters and evaluation of the corresponding permeabilities of the samples. The parameters investigated included measures of the average size, dispersion, skewness, peakedness, and modality of the sample distributions. Several graphs were developed that related permeability to the various statistical parameters. On the basis of these plots a group of curves was defined to predict laboratory permeability values for aquifer samples with random statistical distribution. This set of prediction curves incorporated only the average size and dispersion, because these parameters best described the relationship between permeability and the grain size properties of the porous mediums. These prediction curves were then used to determine the laboratory permeability coefficients for a group of samples obtained from a natural aquifer, and the results were compared with actual permeability values obtained from laboratory tests.