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The hydro-mechanical processes of a reconstituted clay shale (Opalinus Clay) were studied and implications for constitutive modelling of swellable clay shales derived. The study aims to provide further insights into these coupled processes. For that, oedometric swelling tests with varying boundary conditions and loading paths, oedometric compression tests under dry and saturated conditions, and permeability tests were performed. The results showed a unique preloading line for the dry state when plotting the void ratio against the vertical stress. For saturated states, this line was shifted to the left (to smaller stresses) which revealed a severe reduction of preloading stress due to saturation. All loading paths converged in a normal compression line (NCL) regardless of the mechanical boundary conditions during saturation. A trend line afne to the NCL was established for swelling pressures at diferent initial void ratios. The infuence of saturation on the mechanical properties became further evident, as the un-/reloading stifness was signifcantly reduced. A linear relationship between volumetric deformation and saturation was found. A severe swelling induced reduction of permeability in the saturated state was demonstrated and confrmed by the analysis of consolidation processes during oedometric loading. The experimental fndings were used to derive fundamental assumptions for constitutive modelling and were discussed within a numerical framework for expansive soils.