Many natural soils and artificial soils are composite soils formed of a range of particle sizes and types. These soils are often difficult to sample and test when following standard site investigation practice thus it is necessary to resort to empirical correlations, most of which were developed for either coarse-grained (e.g. clean sands) or fine-grained (e.g. pure clays) soils. The hydraulic conductivity of clean sands is a function of the void ratio and particle size distribution, and for clays, the clay type and void ratio. This suggests that the hydraulic conductivity of composite soils will be a function of these properties and the clay content. Composite soils formed of four clay minerals and two sands were consolidated from slurry to determine the variation of hydraulic conductivity with clay content, clay type and void ratio. With matrix dominated soils, soils that contain with more than 35% fines content, the flow is a function of the matrix void ratio and clay type; and, for clast dominated soils, soils that contain less than 20% fines content, the intergranular void ratio and particle size distribution. The behaviour of soils with a fines content between 20% and 35% depends on the confining pressure and density.

This paper presents the results of the electrical conductivity measurements of sand-clay mixtures that were formed of three types of sands and five pure clays and prepared with water of low salinity. The results show that an increase in clay content results in an increase in the overall electrical conductivityeither. Moreover, a direct or inverse relationship between the overall soil electrical conductivity (σT) and porosity (n) has been observed depending on whether the water conductivity (σw) is higher or lower than the clay particle surface conductivity (σs). The common predictive models on electrical conductivity were developed for sands and clayey sands with a clay content of less than 20%. This research has extended these studies to include clays, sandy clays, and clayey sands to show that it is possible to predict the electrical conductivity of a soil from its composition and fabric.