Hydro-Mechanical Characterization of a Shale by Unusually High-Pressure Oedometric Tests

The note presents selected results of an experimental campaign conducted with the aim to investigate the hydro-mechanical behaviour of a shale recovered at a depth of about 900 m below the ground. High-pressure oedometric tests were performed to investigate the stress-strain behaviour and the swelling potential. Moreover, constant-head permeability tests were performed using a specially modified oedometric cell oedometric cell. The obtained results highlighted the anisotropy of the behaviour of the geomaterial. Samples recovered parallel to bedding are characterized by yielding stress, compressibility index and swelling index higher than the ones obtained on the sample recovered perpendicular to the bedding. At the same time, the swelling potential increased in the direction parallel to the bedding and with the decrease in the initial density of the geomaterial. However, regardless of the flow direction, the geomaterial showed consistently very low hydraulic conductivity. The collected results provided fundamental elements for the safety case of underground construction of deep radioactive waste repositories in deep Opalinus Clay shale.