FEM/XFEM modeling of the 3D fracturing process in transversely isotropic geomaterials

This paper studies the fracturing process in geomaterials in order to define the mechanical properties of elements belonging to the lithosphere, such as the kaolonite-rich Opalinus Clay (OPA) formation, due to its potential application as host rock for radioactive waste. For the sedimentary genesis, this rock can be considered a transversely isotropic geomaterial, as also documented in the experimental literature. The fracturing problem is here tackled computationally for a Semi-Circular Bending test (SCB), by resorting to a classical Finite Element Method (FEM) combined with a cohesive zone modeling, or a more advanced eXtended Finite Element Method (XFEM). The selected approaches are successfully compared despite the different computational demand and complex nonlinear nature of the problem. A parametric investigation checks, also, for the possible influence of the notch shape on the fracturing behaviour of the specimen, both in terms of peak load and direction of propagation of the crack within the specimen.