Effect of Air Entrapment on Unsaturated Flow in Porous Media

Abstract

The sizes and connectivity of the pores in porous media such as rock and soil are randomly distributed at microscopic level. Due to this characteristic, the flow of fluids in the porous media is significantly different from the flow characteristics in the ideal single pore model. As important features of seepage, capillary hysteresis and air entrapment generally occur in the porous media experiencing non-monotonic change of water content. Based on the analysis of drying/wetting processes in unsaturated soils, a theoretic model of seepage is developed, in which the effect of air entrapment is taken into account. The theoretical model is implemented into a computer code and a numerical analysis procedure is developed. The model can be used to simulate the unsaturated seepage in soils with the effect of air entrapment under arbitrary change of water content. By comparing the numerical results with measured data, it is shown that the effect of air entrapment is significant on the fluid distribution. The effect of capillary hysteresis and air entrapment should be taken into account in seepage analysis in order to accurately predict the soil-moisture characteristics of soils.