Applications of a micro-structured brittle damage model to laboratory tests on rocks

A multiscale microstructured brittle damage model is used to describe the behavior of confined rock materials. Plane strain and triaxial tests conducted at the laboratory scale are simulated in terms of boundary value problems. Simulations reveal good predictive qualities of the model to describe the macroscopic features of specimens at failure. The microstructures, oriented in different directions, allow the localization of the macroscopic strain along straight lines, emerging at the macroscale in the form of shear bands. The microstructured material model, characterized by recursive equidistant parallel cohesive-frictional faults, is fully defined by six elastic and inelastic material constants. The model was originally developed in a finite kinematics framework to simulate the dynamic behavior of confined brittle materials (Pandolfi et al. in J Mech Phys Solids 54:1972–2003, 2006). In linearized form, it has been extended and used for the simulation of in-field excavations (De Bellis et al. in: Eng Geol 215:10–24, 2016). The performance of the model in predicting the behavior of small scale rock tests in the laboratory, the object of the present study, has never been investigated. Numerical simulations show that the model is able to capture several important features observed in rocks, in particular the reduction of the overall stiffness for increasing deterioration of the material, fragile to ductile transition, strain localization, shear band formation, and more general size effect.