考虑气相影响的降雨入渗过程分析研究

Analysis of rainfall infiltration process considering influence of pore air pressure

降雨入渗过程是水在下渗的过程中驱替空气的水-气二相流过程,对这一过程的精确模拟一直是渗流计算的难点,目前的处理方法通常是忽略孔隙气压力变化的影响。根据多相流理论,结合质量守恒定律和达西定律,建立了水-气二相流模型,模型的求解采用积分有限差分法和Newton-Raphson迭代方法,通过变换主要变量来表达相态的变化,实现了水相、气相边界条件及降雨入渗边界的精确模拟。利用上述模型对一土柱试验进行模拟,从而验证了模型的正确性,研究了一均质土层的降雨入渗过程,得到了孔隙水压力、孔隙气压力和毛细压力及含水率的变化过程。根据入渗率与地表孔隙气压力的变化关系,验证了孔隙气压力的增大对入渗水流产生阻滞作用。在求解非稳定渗流问题中,考虑空气压力变化的影响是值得研究的。

Rainfall infiltration is a process of water flow driving air flow through unsaturated soil, which is a difficult to exact simulate numerically in geotechnical engineering and the influence of pore air is ignored. In this paper, a water-air two-phase flow model is proposed based on the water-air mass balance equations, Darcy＇s law and multiphase flow theory. The integral finite difference method and Newton-Raphson iterative method are used to solve the water-air two-phase model. By switching primary variables, a set of phase state （single phase and two-phase） are taken into account. The refined treatments of every boundary condition are described in detail. The water-air two-phase flow model is verified by simulating an experiment of water through an earth column. The process of rainfall infiltration is simulated numerically. The variation of pore water pressures, pore air pressure, capillary pressure and saturation of water and air phase in different depth of the soil are described; and it is verified that the water-air two-phase flow model is a better model to perform transient seepage problem; and airflow will obstruct water flow from infiltrating into the soil.