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. •Estimation of wetting hydraulic conductivity, kw, from SWCC.•Reduction in wetting kw due to the “rain-drop” effect.•Reduction in wetting kw due to the “ink-bottle” effect.•Proposed method is applicable for the sandy soil.