Theoretical and computational investigation of the fracturing behavior of anisotropic geomaterials

The fracturing process in geomaterials is studied to characterize a potential host rock for radioactive waste, such as the kaolinite-rich Opalinus Clay formation. Because of its sedimentary genesis, this rock can be considered as a transversely isotropic geomaterial. A semi-circular bending test is here modeled based on the eXtended Finite Element Method (XFEM), to check for the formation and propagation of cracks in the rock, with a particular focus on the effect of notch dimensions and scale effects on the fracturing response of the specimen in terms of peak load. Starting with the XFEM-based results, a novel analytical formulation is also proposed to approximate the response of the material in terms of load-crack mouth opening displacement. The proposed formulation is also capable to provide a reliable estimate of the peak value and time history response, compared to some experimental predictions from literature, starting from a predefined value of initial notch depth, which could represent a useful theoretical tool for design purposes.