Analytical Analysis of Rainfall Infiltration Mechanism in Unsaturated Soils

To improve the understanding of the influence of hydraulic properties and rainfall conditions on rainfall infiltration mechanism and hence on the pore-water pressure distributions in single and two-layer unsaturated soil systems, an analytical parametric study has been carried out. Parameters considered in this study include saturated permeability $\left(k_s\right)$, desaturation coefficient ($\alpha$), water storage capacity $({\theta }_s-{\theta }_r)$, and antecedent and subsequent rainfall infiltration rate ($q_A$ and $q_B$). Moreover, the influence of soil profile heterogeneity is also investigated. The calculated results demonstrate that the infiltration process and pore-water pressure response are primarily controlled by both $q\alpha /k_s$ and $k_s/\alpha$. Generally the larger the value of $q\alpha /k_s$ , the greater the reduction of negative pore-water pressure in shallow soil layer. The larger the ratio of $k_s/\alpha$, the faster is the advancement of wetting front. Among the three hydraulic parameters, the effects of $\alpha$ and $k_s$ on pore-water pressure response are much more significant than that of $({\theta }_s-{\theta }_r)$. However, the relative importance of $k_s$ and $\alpha$ depends on the initial negative pore-water pressure range in the ground. In addition, the influence of antecedent infiltration rate $\left(q_A\right)$ on pore-water pressure response appears to be much more significant than that of subsequent infiltration rate $\left(q_B\right)$.