Abstract:

The fundamental mechanisms responsible for drying/wetting hysteresis in the relationship between metric suction and water content, and relevant computational method were studied. The difference between drying and wetting contact angles was considered as the principal factor in terms of microscopic view. Then, based on thermodynamic principle and the assumption that the meniscus among soil particles is a crown face, the iteration relation of filling angles was deduced by studying geometrical properties and taking into account the factors such as radius ratio of soil particles and wetting/drying contact angles. And the relationship between suction and volume of filled water among soil particles with different radii was developed by introducing formulas which solve intensity of pressure on meniscus and volume of filled water. The soil-water characteristic curves (SWCCs) of single meniscus and soil particles with different accumulation styles were solved; the results indicate that: the change of contact angles will cause the hysteresis of SWCCs; filling the pore between particles will raise the water content in lower suction status; and it is more remarkable for loose particles, in which the water content can be enlarged by 90%; the influence of accumulation style and graduation of soil particles on hysteresis is paltry comparatively. Besides, the hysteresis loop of SWCCs can not be interpreted only by hysteresis of contact angles, the relevant theory still under developing.

Key words: unsaturated soil, SWCC, hysteresis, meniscus, contact angle