The influence of different hydro-mechanical paths on final properties of saturated MX80 bentonite samples

Compacted bentonite is considered to be used for deep geological nuclear waste disposal due to its isolation properties such as low permeability, solute retention and swelling pressure. To ensure that these properties will remain favourable throughout the long-term performance, understanding its physical behaviour in front of environmental variables is paramountThe study of expansive soils in geotechnics and geomechanics has been historically motivated because of the damage related to foundations during wetting and drying cycles. In recent decades, research has also been driven by the foreseen use of these materials, in particular bentonite, as buffers in nuclear waste disposal concepts. In this context the main behaviour to be predicted is the swelling pressure development, which will condition the microbial activity and the sealing. The characterisation of material was done determining: the evolution of macroscopic parameters (such as axial strains, void ratio and, in case of isochoric saturation, swelling pressure) upon wetting; initial and final total suction; initial and final degree of saturation; as well as, by analysing the structure of bentonite in initial and final state on the base of XCT image data. Tests were conducted is such a way that the influence of possible side factors such as crushing the grains upon compaction of dry material and cracks evolution upon drying were avoided.