An understanding of thermal effects on mechanical behavior of crystalline rocks is important for many underground projects, such as enhanced geothermal systems, nuclear waste repositories, CO2 sequestration and underground coal gasification, where the temperature can be up to 300 °C or even approach the melting point of rocks. A large number of laboratory tests have been conducted to study the thermal effects on mechanical properties of crystalline rocks, like granites, which showed that elastic modulus, compressive and tensile strengths generally decrease with increasing temperatures. It is known that the rock mechanical behavior is dependent on the formation, growth and eventual interaction of micro-cracks, but the responsibility and mechanism of micro-cracking caused by thermal loading for the macroscopic mechanical properties of granites are still not clear. In this study, particle mechanics method is used to simulate the thermal cracking processes in granite at a scale of laboratory test, in order to elucidate the changing macroscopic mechanical properties with increasing temperature from the point of view of micro-cracking. The main conclusions are:
a monotonous increasing temperature (heating) can generally reduce the elastic modulus, compressive and tensile strengths of granite, mainly by increasing thermal stresses and secondarily by generating tensile micro-cracks.
Compared with heating, the heating-cooling cycles can have a less significant influence on the rock mechanical properties, which is solely due to the increase density of thermal-induced micro-cracks.
