Numerical Procedure for Simulating the Two-Phase Flow in Unsaturated Soils with Hydraulic Hysteresis

Abstract

When modeling the seepage process in a variably saturated porous medium, it is crucial to properly characterize the effects of hydraulic hysteresis. In this paper, a theoretical model of two-phase flow in porous media is introduced, in which an internal state variable-based model of capillary hysteresis is incorporated. Using this theoretical model, a fully coupled finite-element procedure is developed and implemented into a computer code. The numerical procedure is used to simulate the two-phase flow in the unsaturated soils experiencing various drying/wetting cycles. The simulative results are then compared with the experimental data available in existing literature, showing that the proposed procedure is capable of simulating the two-phase flow processes in the porous media subjected to arbitrary drying/wetting cycles. It is demonstrated that under a nonmonotonic flow condition, the effects of hydraulic hysteresis on the water infiltration and redistribution processes in a soil-column test are significant, and in addition, the effects of air phase cannot be neglected. Noticeably, the proposed procedure can be used to track the hydraulic paths that a soil layer experiences, and hence, the procedure is useful in modeling the water infiltration and moisture redistribution processes in soil layers during a long-term intermittent precipitation event or nonmonotonic underground water-table variation.