Hydraulic conductivity of composite soils

Many natural soils (e.g. glacial tills, residual soils, and alluvial soils) and artificial soils (e.g. engineered fill, environmental barriers) are formed of a range of particle sizes and types. These soils are often difficult to sample and test when using standard site investigations thus it is necessary to resort to empirical correlations; most of which were developed for coarse-grained (e.g. clean sands) or fine-grained (e.g. pure clays) soils. The hydraulic conductivity is dependent on the void ratio, clay type and particle size distribution and, in the case of composite soils it is also dependent on 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. The matrix dominated soils, the flow is a function of the matrix void ratio and clay type; and, in clast dominated soils, the intergranular void ratio and particle size distribution. The transition from a matrix dominated soil to a clast dominated soil occurs at a fines content between 20% and 35%.