Anisotropic behaviour of shallow opalinus clay

Opalinus Clay shale, the selected host geomaterial of a high-level radioactive waste repository in Switzerland, was sourced at shallow depth in a borehole in the northern part of the country. Pairs of specimens, retrieved from the same depth were prepared to be tested in oedometric conditions, with loading in the direction either parallel or perpendicular to the bedding planes. The results showed a marked anisotropy of the material response in the low effective stress ranges (