The use of particle size distribution by surface area method in predicting the saturated hydraulic conductivity of graded granular soils

The hydraulic conductivity (k) of a fully saturated granular material can be predicted by the well-known Kozeny–Carman formula, and its slightly different variations, based on the porosity (n) and effective diameter (d_eff). Most variations of the Kozeny–Carman formula compute the parameter d_eff based on a given conventional particle size distribution by mass (PSDm), where the validation would normally be carried out by comparing against laboratory permeability tests conducted on soils having an average coefficient of uniformity (C_u) of about 3. Knowing that the Kozeny–Carman formula was originally developed for uniformly graded materials, inevitable limitations are inherited when it is applied to increasingly graded soils. This study proposes to convert the PSDm into its equivalence in surface area (PSDsa) conforming to the fundamental geometric assumption by which the Kozeny–Carman equation was originally formulated. The estimated d_eff based on this proposed PSDsa method appears implicitly to incorporate the size, shape and angularity of the natural grains which were traditionally represented by the shape coefficient (α). The results presented in this paper show that the suggested method is capable of predicting k for fully saturated granular soils with C_u of up 20.