A simple method for predicting the hydraulic properties of unsaturated soils with different void ratios

•Void ratio is a major factor that affects the hydraulic properties.•A method to normalize the SWRCs with different void ratios is proposed.•A simple method to simulate the hydraulic properties is developed. Reliable estimates of the unsaturated soil hydraulic properties are needed in many research and engineering projects. The void ratio or bulk density is an important factor affecting the unsaturated soil hydraulic properties. The bulk density of one soil can change considerably due to the influences of rain, irrigation, and traffic compaction. It remains a difficult task to accurately describe the hydraulic hysteresis of the unsaturated soil with different void ratios or bulk densities. The aim of this study was to evaluate hydraulic hysteresis behavior and permeability of unsaturated soil with different void ratios or bulk densities based on the normalized soil water retention curves (SWRCs) method. After the normalization, the normalized main drying and wetting SWRCs are independent of the void ratio or bulk density. The hysteresis behavior between the normalized main drying and wetting SWRCs can be described by referring to the existing void ratio independent hysteresis model. Additionally, a simple estimation method to simulate the effects of the void ratio or bulk density on the relative permeability coefficient of unsaturated soils is proposed. The approach proposed here requires no additional parameters. The results show that the proposed hysteresis model can be used to describe the arbitrary main drying, wetting, and scanning curves at arbitrary void ratios over a wide suction range, and the predictions for the relative permeability coefficient with different void ratios by the proposed permeability model can match the experimental data well.