Hydro-Mechanical Behaviour of a Sand-Bentonite Mixture for the Confinement of Nuclear Wastes

The established concept for the protection of the biosphere from high-level nuclear wastes consists in the use of multi-barrier systems in deep geological repository, for which clayey geomaterials are key elements. Bentonite-based materials are selected as buffer and backfilling materials. Once in place, the barriers will be subjected to a series of severe loadings, including strong variations of suction (i.e. wetting and drying cycles). The paper presents selected results from a large ongoing research work to investigate the behaviour of bentonite-based materials in the context of nuclear waste disposal. In particular, the paper focuses on the response of a Sand/Bentonite mixture under different hydro-chemo-mechanical loadings. Performed experiments include free and confined swelling tests and controlled-suction confined swelling tests, along with an assessment of the fabric evolution during those loadings. Different dry densities and waters of different salinity were considered in the experiments. The obtained data combined with results from other studies allowed to define a trend for the calculation of the swelling pressure as a function of the relative dry density of the bentonite in the mixture.