Modeling the swelling curve for packed soil aggregates using the pedostructure concept

The swelling curve is generally studied as structural soil volume dependence on water content during swelling, and not on time. In this paper, we show how the swelling curve defined as the specific volume of the soil as a function of time, V(t), represent the dynamic properties of the pedostructure where the shrinkage curve represents and characterizes the hierarchical and functional organization of the soil medium. This paper presents the development and experimental evaluation of the swelling curve for a dry bed of packed aggregates immersed in water using the pedostructure concept. Pedostructure-based parametric functions for the soil structure and water interaction represented by soil shrinkage and matric water potential curves were used to derive the swelling curve equation. This equation represents the kinetic of absorption of water by swelling of the primary peds within the pedostructure. Experiments on wetting-drying cycles of reconstituted soil samples were conducted to obtain the parameters needed for the swelling curve equation. The simulated swelling curves using the derived equation agreed well with the measured data. The new swelling equation shows only one additional parameter; namely, the time to half charge, t(1/2), which seems to be a characteristic of the clay type. It was found to be near 2100 s for kaolinitic soils and found to be independent of the clay content; as it decreased by a factor of two to three due to the presence of smectites in the sample. This paper gives access to the study of the kinetic of water absorption by primary peds