The constitutive behaviour of the Opalinus Clay is well understood. Geomechanical properties and volumetric ("swelling") behaviour are particularly favourable for self-sealing (Section 5.7).
The Opalinus Clay exhibits comparable mechanical properties in the three siting regions, but peak strengths are clearly different from the shaly facies of the Mont Terri rock laboratory. The different burial history (greater burial depth and lower tectonic overprint) has led not only to higher overall strength than in Mont Terri, but also to a lower variability.
Deformation tests with the Opalinus Clay and confining units, as well as aquifer limestones, are consistent with observed effects of mechanical layering (Sections 4.3 and 4.4) and highlight that fracturing has a much greater effect on the more competent rocks than for the Opalinus Clay.
Deformation in clay-rich rocks is typically expressed by more distributed strain and step-overs in contrast to more localised discrete strain accommodation in stiffer units.
Segmentation of fault structures in the Opalinus Clay is expected to hinder fault-related flow.