Based on the theory of subcritical crack growth, Linear Elastic Fracture Mechanics (LEFM), and Charles equation, a lifetime (time to failure) prediction scheme has been developed for rock specimens containing initial microcracks under constant loadings. It is assumed, that the macroscopic failure of the rock is the result of the coalescence of many small micro-cracks at the grain size level. The damage process was modeled and macroscopic fracture pattern of the rock specimens were studied through numerical modeling. Lifetimes were predicted; typical fracture patterns were observed in the numerical models. Factors influencing the predicted lifetime were studied. Conclusions were drawn and possible improvements to the future research work were proposed.
The long term stability of geotechnical structures such as tunnels, mining shafts etc. has long been an important issue for safety considerations. As rock is the main load-bearing material in such structures, the lifetime (time to failure) of rock under load is of great practical interest for engineers and researchers. Time dependent behavior of rock has been studied by many researchers (Kemeny 1991, 2003,2005, Sun & Hu 1997, Eberhardt 1998, Shao et al. 1999, Malan 1999, 2002, Aubertin et al. 2000, Masuda 2001, Miura et al. 2003, Chen et al. 2004, Chandler 2004, Shin et al. 2005, Amitrano & Helmstetter 2006, Lei et al. 2006, Jeong et al. 2007, Li et al. 2008, Damjanac & Fairhurst 2010, Jiang et al. 2012, Lu et al. 2014). Konietzky et al. (2009) proposed a lifetime prediction approach for brittle rocks under constant load. Numerical calculations were performed to simulate the time-dependent propagation and coalescence of microcracks, which finally lead to the failure of the rock. As a further development of this research work, this study improved the existing approach by introducing new crack propagation mode and stress intensity factor calculation scheme. The proposed scheme is studied through numerical simulations.
