Estimation of the wetting scanning curves for sandy soils

It is known that the soil-water characteristic curve (SWCC) of unsaturated soils is hysteretic. The engineering properties of unsaturated soils during the drying process are different from those during the wetting process, and the difference can be related to the hysteresis of the SWCC. Therefore, understanding the hysteresis of the SWCC is crucial in engineering practices. In this paper, both the “rain-drop” and “ink-bottle” effects on the hysteresis of the SWCC are quantified with mathematical equations. In the proposed equations, it is assumed that soil volume changes during the drying and wetting processes are negligible, which is a reasonable assumption for most sandy soils. Based on the proposed theory, the wetting scanning curves were estimated from the main drying curves. The results from the method proposed in this paper have been compared with experimental data from the published literature. Satisfactory agreements were found between the measured and estimated wetting scanning curves. Consequently, the method for estimating the wetting scanning curves from the fitting parameters of the SWCC by using the equations proposed in this paper is recommended.