On the swelling potential of compacted high plasticity clays

In earthworks engineering, predicting the influence of the water content and the dry density on compacted soils deformation is a fundamental issue, which is particularly important for the use of clays in embankments. This paper presents the experimental results and a microstructural interpretation of swelling tests performed on four clays, compacted at different water contents and dry densities. The influences of dry density and water content on the swelling potential are described, showing the coupled effect of these two parameters. In order to quantify this coupling, the initial air void ratio is defined and it is observed that this air void ratio has an apparent linear relationship with the void ratio after swelling. This observation enables analysing all the tests in a synthetic manner, by plotting the origin ordinate and the slope of the linear relationships versus the initial hydrous state.Moreover, one of the clays microstructure was analysed using mercury intrusion porosimetry (MIP). The results show that swelling leads to a micropores increase and a macropores decrease. In addition, micropores volume increase does not depend on the initial dry densities, whereas the macropores volume increase does.For further discussion, a simplified microstructural model is proposed allowing the interpretation of the soil swelling using MIP results. The comparison between the model prediction and the microstructure observation supports the interpretation of the swelling tests and shows that the origin ordinate and the slope of the relationship between the initial air void ratio and the final void ratio can be linked to micropores and macropores volume variations. However, the comparison also shows that the simplified microstructural model presents some limitations when applied to very dry or wet soils.