Study of Soil-Water Characteristic Curve Using Microscopic Spherical Particle Model

When variations occur in the water content or dry bulk density of soil, the contact angle hysteresis will affect the soil-water characteristic curve (SWCC). The occurrence of the contact angle hysteresis can be divided into slipping and pinning. It is difficult to determine the effect of pinning existence on SWCC by tests. In this study, the effect of contact angle hysteresis on SWCC was analyzed either in the case of no variations in soil dry bulk density with changes in soil water content or no variations in soil water content with changes in soil dry bulk density. In both cases, soil particles were simplified to the spherical particle model. Based on the geometrically mechanic relationship between the particles and connecting liquid bridges, a physical model for predicting the SWCC was derived from the spherical particle model. Adjusting parameters made the model applicable to various soils, that is, the cohesive soil was considered as micron-sized spherical particles. Through the simulations on SWCC test data of sand, silt, clay, and swelling soil, it was confirmed that the physical model possessed good reliability and practicability. Finally, the analysis of rationality of contact angle was performed based on the basic assumptions of the model.