3. Experiments on strength and softening response of rock
Mechanical behavior of rock is reviewed and approaches to measure material and system response are highlighted. A non-traditional testing method that involves biaxial deformation developed through a Vardoulakis-Goldscheider plane strain apparatus is used to assess dilatancy and friction, as well as dilatancy of the shear band after localization. The Paul-Mohr-Coulomb failure criterion, which includes the intermediate stress, is applied to interpret the stress states at failure. Post-peak response, often referred to as softening, is explained as a size effect using a cohesive crack model.