Assessing Hydraulic Hysteresis Models to Characterize Unsaturated Flow Behavior under Drying and Wetting Conditions

Abstract

A soil-water retention curve (SWRC) is one of the important constitutive laws for soil-water distribution and shear-strength assessment in unsaturated soil. A SWRC commonly shows the hysteretic behavior under drying and wetting conditions. Several mathematical models have been developed to describe hysteresis, including a model commonly presented in the literature and implemented into HYDRUS software. Recently, the authors developed a new hydraulic hysteresis model for which only one additional parameter was introduced to capture the effects of capillary and air-entrapment hysteresis. To confirm the capabilities of the two models in analyzing the unsaturated flow, the authors’ model was implemented with a numerical code using the FORTRAN language. The numerical codes including the authors’ model and the model in HYDRUS for hysteresis assessment were used to analyze the same transient unsaturated flow problems under drying and wetting conditions. By comparing the measured data to curves predicted by the two models, the results show that the hysteretic SWRC cannot be described correctly when the effects of hydraulic hysteresis are ignored under drying and wetting conditions. Moreover, the comparison between the results predicted by the two models shows that the authors’ model gave a robust performance for capturing hydraulic hysteresis behavior in unsaturated flow.