Analytical Model of Soil-Water Characteristics Considering the Effect of Air Entrapment

Based on experimental data and the flow property analysis of the drying-wetting process of fluids under a microscope, a theoretical model is developed to consider the effect of air entrapment in the soil-water retention constitutive relationship. The effect of hysteresis on the fluid flow is considered by introducing an integrated capillary hysteretic model. There are only three conditions needed in the new model, i.e., the primary drying boundary curve, the main wetting boundary curve, and one point in the main hysteretic loop. Furthermore, as long as the previously experienced maximum matric suction in the porous medium is given, the model is capable of simulating changes of the soil-water state with the effect of air entrapment undergoing an arbitrary change of matric suction. By comparing the predictive curves with measured data from the literature, it is shown that the effects of air entrapment and capillary hysteresis are significant on the soil-water retention relationships. The model with the effects of capillary hysteresis and air entrapment should be taken into account in the soil-water relationship in order to accurately predict soil-moisture states in porous media. (C) 2014 American Society of Civil Engineers.