| The unsaturated zone is a tie connecting the surface water and the groundwater system, which plays an important role in hydrological processes. With precise analysis of unsaturated flow, the unsaturated seepage analysis has developed from the single-phase flow to the complicate multi-phase flow. In hydraulic engineering and rock soil engineering, to determine the amount of surface runoff, clarify the formation mechanism of underground water, and analyze the unsaturated slope stability, further research of the moisture movement patterns in unsaturated zone has a great meaning on theory and in practice.Based on a balance of mass, a balance of linear momentum and a balance of moment of momentum satisfied by the liquid phase and gas phase in unsaturated soils, a water-air two-phase flow model was applied, to simulate the infiltration law, Lisse effect and the slop stability induced by rainfall in the unsaturated soil. The main research contents and innovative results are as follows:(1) The water-air two-phase flow model in the unsaturated soil was developed. The numerical treatments of the initial condition and the boundary condition were also presented. And by comparing with the experiment results of ponding infiltration, the simulated results agree well with the experiment results, indicating that, the water-air two-phase flow model can reflect the infiltration law to some extent in the unsaturated soil, and has a physical meaning.(2) Based on the water-air two-phase flow model, considering the influence of the pore-air, the moisture movement patterns in the unsaturated soil under rainfall were simulated, including the distributions of water saturation, pore water pressure, pore air pressure and capillary pressure, the variations of infiltration rate, surface runoff amount and infiltration amount, the Lisse effect, and the groundwater recharge variety. Besides, the influences on rainfall infiltration were also analyzed, which included: rain intensity, air entry value, degree of soil uniformity and intrinsic permeability.(3) According to the seepage calculated by the water-air two-phase flow model, and based on an improved unsaturated soil shear strength theory, the equation describing the safety factor for the given slip surface was derived. So the unsaturated slope stability was anayzed, considering the influences of pore-air pressure and capillary pressure. Firstly, the variation of the safety factor on the given slip surface, the safety factor contributions from the pore-air pressure and the capillary pressure, and their relationships with the total air pressure and the total capillary pressure acting on the slip surface were discussed, respectively. Then the variations of the safety fator under different rain intensities, air entry values, degrees of soil uniformity and intrinsic permeabilityies, were also studied. |
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