In the context of deep nuclear wastes storage deep galleries will be backfilled with clay-based materials. These backfill must have specific hydromechanical properties to prevent water circulation along the repository after its closure. The backfill material will be partly made from the excavated material, i.e. Callovo-Oxfordian argillite that would have been stored at surface during the exploitation period, and mixed with sand to reach the target design properties. The hydromechanical properties of the backfill must remain stable over time. It is thus necessary to determine the relative impact of several factors such as the setting conditions, nature and dosage of treatment product, etc. on the properties of the backfill. The thesis will be focused at understanding the cross relationship between macroscopic hydromechanical properties, the reorganization of the material microstructure due to the swelling of clay particles upon hydration as well as the alteration processes associated to the circulation of alkaline water.

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