Sand/bentonite (S/B) mixtures are considered as backfilling materials for nuclear waste storage. The paper presents an experimental campaign that was carried out to investigate the swelling behavior of a S/B mixture, under different hydro-chemo-mechanical loadings. Performed experiments include free and con-fined swelling tests and controlled-suction confined swelling tests. Different dry densities and waters of dif-ferent salinity were considered in the experiments. The fabric evolutions associated with the swelling behav-iour was investigated by combining mercury intrusion porosimetry analyses and scanning electron microscope photomicrographs. The swelling potential was found to be sensitive to variations in compaction dry density, applied matric suction and pore water salinity. The pore size distribution (PSD) of the compacted specimens was found to be bimodal, irrespective of the dry density or of the water used for the preparation of the mix-ture. Tests on specimens compacted at the same dry density and saturated with different types of water under constant volume conditions have revealed how with increasing salinity of the solution, the final PSD moves from a mono-modal to a bi-modal distribution. 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.