EFFECT OF CAPILLARY HYSTERESIS ON TWO-PHASE FLOW IN POROUS MEDIA
(1. State Key Laboratory of Geomechanics and Geotechnical Engineering，Institute of Rock and Soil Mechanics，
Chinese Academy of Sciences，Wuhan，Hubei 430071，China；2. Central Southern China Electric Power Design Institute，
Abstract：The seepage process in porous media is significantly influenced by water content and drying/wetting history that the material has experienced. Based on the continuum theory of porous media and an internal state variable-based model of capillary hysteresis，a two-phase flow model of porous media is created and implemented into the U-DYSAC2 finite element code. Comparing with the experimental data，the results show that the proposed model can be reliably and efficiently used to simulate the unsaturated seepage problems of porous media under complex conditions. The new procedure is used to analyze the seepage processes in a soil slope subjected to drying/wetting cycles. The results show that the effect of capillary hysteresis on unsaturated seepage process is significant；and the hydraulic state of soil is not only related to the current value of water content or matric suction，but also depends on the drying/wetting history that the soil has experienced. In particular，it is shown that if the main drying soil-water characteristic curve is adopted in the analysis，the matric suction of soil will be over-predicted；hence the shear strength of soil and the factor of safety of slope stability can be over-estimated based on the traditional methods of stability analysis. Therefore，it is necessary to take into account the effect of capillary hysteresis in modelling unsaturated seepage problems.