Porous materials like soils are susceptible to volume change either by external or by internal forces. Internal forces can be considered as self-organising forces, which control the arrangement of particles as a result of changing water contents or water potentials, respectively. Generally, these changes are accompanied by volume change due to swelling and shrinkage. The understanding of volume change of soils due to shrinkage is necessary to characterise the formation and density of cracks, and hence the development of soil structure, as well as to apply this knowledge to model the hydrology of porous media more precisely.

Tensile stresses are the driving factor for shrinkage. As they are a function of water potential, this stress state variable may be used to model volume change together with a change in the water status. It has been shown previously that it is possible to use generally available hydraulic models for predicting volume change. When combining this relationship with the water retention curve, the shrinkage curve based on the variable water potential will be the result. Using continuous functions to predict the shrinkage curve allows the interpretation of these functions and the derivation of characteristic values defining and describing the mechanical and hydraulic behaviour of soils, using water potential as the main variable.

This method will be explained and examples will be given, which shows the possibilities for modelling and interpreting shrinkage curves.