土体初始饱和度对降雨入渗的影响

Effects of initial degree of saturation of soil on rainfall infiltration

基于水、气两相流理论,采用有限单元法计算了壤土在不同饱和度下的降雨入渗过程,以研究初始饱和度变化对降雨入渗的影响。数值模拟结果表明:降雨入渗初期孔隙气压会逐渐增大,入渗强度会因孔隙气的顶托作用逐渐减小并最终趋于稳定。稳定后的降雨入渗强度主要取决于土体基质吸力和渗透特性,与土体初始饱和度大小直接相关;入渗强度存在最大、最小值,最大值通常会出现在初始饱和度为0或1时,而最小值所对应的饱和度与土体非饱和特性有关;受土体基质吸力和水、气渗透性的双重影响,入渗强度会先随饱和度的增大而逐渐减小,当降至最小值后,入渗强度又会随饱和度的增大而增大。根据计算结果,提出了一个可计算相对稳定入渗强度的公式。

Based on the theory of gas-liquid two-phase flow, the finite element method was used to simulate rainfall infiltration in loam soil with different degrees of saturation to investigate the effects of the initial degree of saturation on rainfall infiltration. Numerical results show that the pore air pressure increases gradually in the initial stage of rainfall infiltration;then, the infiltration rate decreases to a stable value because of the jacking force caused by pore air. The stable infiltration rate is mainly determined by the matrix suction and permeability characteristics of soil, varying with the initial degree of saturation. With the variation of the initial degree of saturation, the infiltration rate reaches its maximum or minimum values. The maximum infiltration rate usually appears in the stage of residual or full saturation, while the minimum infiltration rate occurs in the unsaturated stage, depending on soil unsaturated characteristics. Affected by the matrix suction of soil and the relative permeability of water and air, the infiltration rate gradually decreases with the increase of the degree of saturation at first. When the infiltration rate drops to the minimum, it starts to rise with the increase of the degree of saturation. According to the results of numerical simulation, a formula is proposed for calculation of the relatively stable infiltration rate for different initial degrees of saturation.