Evolution and failure of the Opalinus clay: relationship between deformation and damage, experimental results and constitutive equation

The rock mechanical properties of the Opalinus clay are investigated in the BGR laboratories. Undrained clay specimens were compressed to study the temperature effects on their strength. Post-failure stresses were observed to drop to 40% of the failure stresses. At 60 °C, the failure stresses were 25% lower than at room temperature. 3D test frame was used to deform unconfined cubic specimens of Opalinus clay in all three principal directions. The test data are used to develop a material law, based on Burgers rheological model. The orthorhombic symmetry of the material requires independent parameters parallel as well as orthogonal to the bedding plane. The modeled strains fit reasonably well to the measured strains, revealing the applicability of the applied method.