Rocks often experience high temperatures (several hundred degrees Celsius) due to underground operations, such as deep geological disposal of nuclear waste, geothermal heat extraction, CO2 geological storage and underground coal gasification as well as deep mining. Laboratory studies have shown that mechanical properties such as compressive strength, tensile strength, elastic modulus, etc. of rocks such as granite, marble and sandstone are temperature and temperature-history dependent. Therefore, the conventional failure criteria may not be suitable enough under high temperature conditions. In the present study, a thermo-mechanical modified Mohr-Coulomb failure criterion is proposed based on the extensive review and interpretation of mechanical properties of granites exposed to high temperatures. The deduced criterion takes into consideration the effects of thermal damage and confining conditions. The numerical study indicates that the proposed criterion provides a higher quality depicting rock strength under high temperatures compared with the conventional Mohr-Coulomb criterion. Moreover, according to analyses of the behavior of other rock materials exposed to high temperatures, this criterion is also suitable for other rocks.
Rock-mechanical engineering in high temperature environments is of universal interests and a challenge to scientists and engineers of different disciplines. Rock mass may undergo high temperatures (several hundred degrees Celsius) in modern projects, such as deep underground nuclear waste disposal (Bergman 1980, Rutqvist et al. 2008), geothermal heat extraction (Zhao 2000, Zhao 2002), geological CO2 storage (Roddy & Younger 2010) and underground coal gasification (Burton et al. 2007, Kühnel et al. 1993), as well as deep mining (Zhou et al. 2005, He 2009). Under the action of high temperature, the micro-structures of rocks change significantly (Dwivedi et al. 2008), new micro-cracks are developed, and pre-existing ones are extended/widened (Den''gina et al. 1994). Meanwhile, various physical and mineralogical changes take place within these rocks.