The influence of the elevated temperature on the evolution of the EDZ (Excavation Damaged Zone) in the rock mass is an important issue for the performance assessment of radioactive waste repositories. The thermal stress-induced additional damage may increase the extent of the EDZ and the degradation of mechanical properties of rock mass around the deposition openings which may provide a preferential pathway for radionuclides to migrate. Laboratory scale biaxial compression tests were performed using 170 mm cubic cement mortar specimens with a circular opening in the center to simulate and investigate the brittle failure process around the underground excavations. Acoustic emission (AE) technique was applied to monitor and characterize the brittle failure process around the circular opening. The experimental observations of biaxial compression tests indicate that brittle failure around a circular opening is mainly a process of progressive spalling and finally results in a v-shaped failed zone. Laboratory scale heater tests were conducted under a confined condition with both intact and pre-damaged cement mortar specimens to investigate the effect of elevated temperature on the damaged zone. The results of the heater test using an intact specimen showed that no clear damage was found on the surface of the circular opening after heating. In contrast, for the heater test using a pre-damaged specimen, it was found that fractures initiated on the surface of the circular opening but no obvious further spalling was identified and these experimental findings are consistent with the field observations from the in situ single hole heating damage test.
The thermo-mechanical response of rock is a critical research issue in many fields such as geological sequestration of CO2 (Shiu et al., 2011), compressed air energy storage (Mohanto et al., 2014), enhanced geothermal systems (Rutqvist et al., 2015) and nuclear waste repository (Tsang et al., 2012) which are usually subject to complex thermo-mechanical conditions. One of the key issues when assessing the performance of the nuclear waste repository is related to the effects of the temperature elevation due to the heat emitted from the placement canister (Pusch, 2008).