A Hysteretic Model Considering Contact Angle Hysteresis for Fitting Soil-Water Characteristic Curves

The soil-water characteristic curve (SWCC) plays an essential role in the analysis of the shear strength, deformation, hydraulic conductivity, and aqueous diffusion of unsaturated soils. A review of methods proposed for fitting the main SWCCs is presented. The methods can be categorized into three groups, namely, (i) empirical methods, (ii) domain methods, and (iii) theoretical methods. A hysteretic model considering the contact angle hysteresis is proposed for fitting the main SWCCs based on a theoretical method. The model links the physical quantities at the micro-and macro-scale. Specifically, a modified expression describing the relationship between the volume of the liquid bridge and the water content is derived, and the contact angle hysteresis behavior is modeled based on the study of total thermodynamic potential energy. The model has a clear physical meaning, and the parameters can be obtained easily. Comparisons of the model simulation and experimental data show that the proposed model accurately captures the main features of the SWCC and describes the nonlinear relationship between the matric suction and the water content during wetting and drying processes. Plain Language Summary The relationship between the matric suction and the water content in the soil is known as the soil-water characteristic curve (SWCC). The SWCC is crucial for analyzing the shear strength, deformation, hydraulic conductivity, and aqueous diffusion of unsaturated soils. The drying SWCC is typically located above the wetting SWCC in a given plane. This phenomenon can be described by the hysteretic behavior of the SWCC. The determination of a complete set of hysteretic SWCCs involves measuring the matric suction and water content during wetting and drying processes. However, these measurements are time-consuming and costly, and the use of raw experimental data without a fitted model is impractical. Therefore, we developed a novel hysteretic model based on the Young-Laplace equation to address these issues. The model links the physical quantities at the micro-and macro-scale and accurately captures the main features of the SWCCs.