The results of a comprehensive experimental program focused on the study of progressive degradation processes on a low permeability argillaceous rock induced by hydraulic cycles is presented in the paper. Relative humidity cycles were applied with vapour transfer technique, and bender elements were used to evaluate the evolution of shear stiffness during the application of hydraulic paths. The characterisation of the material included the determination of the water retention properties (water retention curve), as well as the pore size distribution using mercury intrusion porosimetry, complemented with SEM micrographs and elemental analysis using X-ray spectroscopy to characterise micro-structural features and detect clayey and non-clayey constituents. Results showed cumulative and irreversible swelling of the samples with the application of relative humidity cycles. Regarding shear stiffness, an important reduction (around 80%) was observed at the end of the hydraulic paths applied. Evidence of rock degradation at macro-scale was linked to structural modifications at micro-level.