ABSTRACT: Changes in the mechanical properties of high thermally loaded gabbro have been investigated in the laboratory to evaluate damage in crystalline rock. Specimens were heated in an electrical furnace within the range of 150°C to 1000°C. After the thermal loading, the specimens were tested in uniaxial compression condition. Test results showed that both the maximum uniaxial strength and theYoung's moduli of rock decreased with increasing temperature. However, the rate of decrease varied depending on the nominal temperatures. While the strength decrease reached 20% at a temperature of 600°C, it suddenly dropped to 50% for 700°C. A drastic decrease was also observed for the Young's moduli of specimens that were heated above 600°C. These results provide insights for a better understanding of the behaviour of a rock mass subjected to high temperature, such as an underground construction that has experienced a fire accident. To illustrate this example, the damage zone calculations show the consequence of thermal loading on the stability of the underground opening.
1 INTRODUCTION In many situations, rock masses may experienced high temperatures that lead to a drastic degradation of their mechanical properties. This can happen for rock at great depth or for near surface infrastructure such as tunnels that have experienced fire accidents. For these infrastructures, it is extremely important to investigate micro-crack propagations and consequent rock damage (Erdakov and Khokhryachkin, 2005). In the last few decades, special attention has been given to thermal damage in relation with rock characterization for underground radioactive waste repositories (Homand & Houpert 1989). Recent laboratory studies, summarized by David et al. (1999), clearly show how thermal cracking modifies the elastic moduli (Heard & Page 1982, Nasseri et al. 2007), permeability (Menendez et al. 1999) and mechanical strength (Homand & Troalen 1984).