Experimental investigations on anisotropy in dilatancy, failure and creep of Opalinus Clay

Deformation behaviour and failure of Opalinus Clay were investigated in the BGR laboratories. True triaxial compression experiments were performed on differently oriented cubic specimens to detect the onset of dilatancy. Both short term strength and dilatancy are influenced by the orientation of bedding planes with respect to the orientation of the stress components. When the maximum principal stress acts normal to the bedding planes the dilatancy boundary is close to the failure boundary. In contrast, both boundaries are clearly different for samples loaded parallel to the bedding planes. The experimental findings show a less pronounced anisotropy of the dilatancy behaviour than of the failure strength. The creep rate of Opalinus Clay is found to be less sensitive to the applied stress as the deviatoric stress is decreased. Bedding plane anisotropy was found to have a greater effect on transient creep than on steady state creep.