Time to Failure Prediction Scheme for Rocks

Excerpt

The lifetime of solids under loads has been studied by many researchers (e.g., Mishnaevsky 1996; Ignatovich 1996; Sun and Hu 1997; Aubertin et al. 2000; Miura et al. 2003; Kemeny 2003, 2005; Guedes 2006; Le et al. 2009; Damjanac and Fairhurst 2010). In this study, the lifetime of rocks under load is governed by microstructural defects such as microcracks. The natural rock contains microcracks which propagate and coalesce under loads. The macroscopic fractures formed by these microcracks could finally lead to the failure of the rock. This process has been simulated by Konietzky et al. (2009), based on cellular automata. As a further development of this research work, this study improved the crack propagation scheme by considering initial crack orientations and wing cracks. The developed scheme is especially valid for cohesive granular material, like rocks, which consists of mineral grains of different shape, size, and mechanical properties, like strength and stiffness. Like seismoacoustic monitoring documents (e.g., Yang et al. 2012; Fortin et al. 2011; Mayr et al. 2011; Yoon et al. 2012), the damage and final failure of rocks are not characterized by the growth of one single crack, but, instead, by the growth and coalescence of many microcracks, which grow at different speeds at the same time. The proposed simulation scheme is an attempt to reproduce this process up to the formation of a final macroscopic failure (macroscopic tensile crack or shear band). As a limitation of the current numerical model, the evaluated lifetime value is influenced by the mesh size. …