Soil properties such as water retention and unsaturated hydraulic conductivity curves controlling fluid flow in soil depend on the particle size distribution (PSD) and soil structure. For soils with a single grain structure the PSD is the most important property for small scale water flow. Amendments of soils with industrial by-products or mixing of sands with clayey materials to reduced water repellency affect hydraulic properties significantly. The objectives of this contribution is to present and test a mixing model that allows the description of hydraulic properties of mixtures of fine and coarse textured soil based on properties of the two pure soils. The bases for describing hydraulic properties are the models by Brooks and Corey and van Genuchten-Mualem which can both be related to the PSD. For our model it was assumed that; i) each substrate of a mixed porous media maintains its own hydraulic properties, meaning water retention (WR) is additive and the hydraulic conductivity depends on the spatial arrangement of the materials; and ii) within a bimodal granular structure the finer materials fills in pore space of the coarser material for the case where the coarse material is grain supported. In the case of a high fraction of fine material the coarse particles float in the fine matrix. The model was calibrated for mixtures of silt-clayed tailings and medium-grained sand at compositions from 10 to 90 % sand or tailings.