Role of Stress History on the Swelling-Shrinkage Behavior of Compacted Scaly Clay

Compacted scaly clays are complex geomaterials widely used for the realization of dam cores and waste dump liners. This research aims to investigate the swelling/shrinkage behavior of these geomaterials subjected in an oedometric cell to complex hydromechanical stress paths, including different sequences of cyclic variations of suction and stress. Microstructure investigations, based on scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) techniques, highlighted the microstructural characteristics of the material, which are the distinctive microfabric features (particles assemblages and scales) and the double-porosity networks, where micro- and macropores coexist. Moreover, the MIP technique, applied to the tested oedometric specimens, provided significant elements supporting the microscale interpretation of the observed behavior on the basis of mechanical interaction between the different levels of microstructural arrangements. In all the cases analyzed, the suction cycles induce a microstructural rearrangement in the macropore domain, enhancing the stability of the fabric of the compacted clay. Suction-controlled oedometric test results were modeled with an elastoplastic constitutive model, which considers the role of a double structure in the behavior of unsaturated soils. The results obtained highlight the mutual influence between wetting/drying cycles and loading/unloading paths on the volumetric behavior of the geomaterial.