A model to predict the water retention curve from basic geotechnical properties

The water retention curve (WRC) has become a key material function to define the unsaturated behavior of soils and other particulate media. In many instances, it can be useful to have an estimate of the WRC early in a project, when little or no test results are available. Predictive models, based on easy to obtain geotechnical properties, can also be employed to evaluate how changing parameters (e.g., porosity or grain size) affect the WRC. In this paper, the authors present a general set of equations developed for predicting the relationship between volumetric water content, theta, (or the corresponding degree of saturation, S-r) and suction, psi. The proposed model assumes that water retention results from the combined effect of capillary and adhesion forces. The complete set of equations is given together with complementary relationships developed for specific applications on granular materials and on fine-grained soils. It is shown that the model provides a simple and practical means to estimate the water retention curve from basic geotechnical properties. A discussion follows on the capabilities and limitations of the model, and on additional tools developed to complement its use.