Estimation of wetting hydraulic conductivity function for unsaturated sandy soil

The occurrence of rainfall-induced slope failures is mainly due to the infiltrated rainwater which reduces the shear strength of soil. The slope is initially observed in an unsaturated condition and it becomes wetted during rainfall. In other words, the infiltration of rainwater into the soil slope is a wetting process. As a result, the amount of the infiltrated rainwater is mainly governed by the hydraulic conductivity of the unsaturated soil under the wetting process. Direct measurement of the hydraulic conductivity of unsaturated soil under the wetting process is time-consuming and costly. On the other hand, there are various available methods or models for the estimation of hydraulic conductivity of unsaturated soil under the drying process. In this paper, the methodology for the estimation of hydraulic conductivity function (HCF) of unsaturated soil under the wetting process based on the drying soil-water characteristic curve (SWCC) is proposed. The proposed method is based on the concept of the pore size distribution function. Both ink-bottle and rain-drop effects on the hysteresis of SWCC are incorporated in the estimation of the HCF of unsaturated soil under the wetting process. The estimated results were verified with the experimental data from published literature.

Automated summary

Rainfall-induced slope failures are mainly caused by infiltrated rainwater reducing soil shear strength. This study proposes a method for estimating the hydraulic conductivity function (HCF) of unsaturated soil during the wetting process based on the drying soil-water characteristic curve (SWCC). The estimation considers ink-bottle and rain-drop effects on the hysteresis of SWCC and was verified using experimental data from published literature.