A pore-water distribution model for the estimation of the hydraulic conductivity of stiff unsaturated soil during the wetting process

It is noted that not only the soil–water characteristic curve (SWCC) exhibits hysteresis in the drying and wetting processes, but the hydraulic conductivity of unsaturated soil also shows a similar characteristic. The experimental measurements of the hydraulic conductivity of unsaturated soil either in the drying or wetting process are commonly time-consuming and costly. Therefore, the hydraulic conductivity of unsaturated soil is commonly determined by using the indirect method. In the previous studies, the drying hydraulic conductivity function (HCF d ) is commonly estimated from the drying SWCC based on the concept of the pore-size distribution. In this study, a new pore-water distribution-based model was proposed to estimate the wetting hydraulic conductivity function (HCF w ) of unsaturated soil. In the proposed model, several factors such as the “rain-drop” effect, “ink-bottle” effect, and entrapped air that may lead to the hysteresis of SWCC were incorporated in the computation of the pore-water distribution in soil during the wetting process. Subsequently, the statistical method was adopted to compute the effective area that allows water flow in an unsaturated soil based on the information of pore-water distribution in the soil. Consequently, a new pore-water distribution-based model was proposed to estimate the HCF w of unsaturated soil. The proposed model shows good agreement with the experimental data from various published literatures.