No abstract

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.

Abstract. The present work investigates the fracturing behavior of an anisotropic layered geomaterial, known as Opalinus Clay (OPA). The formation of this rock is mainly related to a sedimentation process, where bedding planes correspond to planes of isotropy. OPA is here studied because of its good properties, primarily, the low permeability and high adsorption capability, which make it a perfect candidate for the storage of radioactive waste. The characterization of this rock takes place experimentally in the Mont Terri Rock Laboratory, in the northern Switzerland, with an increased attention to theoretical and computational predictions. In this context, this work aims at simulating the nonlinear crack behavior of OPA by using the eXtended Finite Element Method (XFEM) and damage mechanics. The study is applied on a Semi-Circular specimen under a Bending load (SCB), whose fracturing response is investigated in terms of peak load and direction of the cracking propagation for different notch dimensions and geometries.