ABSTRACT
The influence of the elevated temperature on the evolution of the Excavation Damaged Zone (EDZ) in the rock mass is an important issue for the performance assessment of radioactive waste repositories. Thermal stress produce additional damage and may increase the extent of the EDZ resulting in the degradation of mechanical properties of rock mass around the deposition openings which provides a preferential pathway for radionuclides to migrate. In this research, cubic specimens with central circular opening were casted using cement mortar. Biaxial compression tests were firstly performed to generate damaged zone around the opening. Acoustic Emission (AE) technique was applied to monitor and characterize the brittle failure process around the circular opening. The experimental observations of the biaxial compression tests indicated that brittle failure around a circular opening was mainly a process of progressive spalling and finally resulted in a v-shaped failed zone. Laboratory scale heater tests were conducted under confined condition using intact and damaged cement mortar specimens to investigate the effect of elevated temperature on the evolution of the damaged zone. The results of the heater test using intact specimen showed that no clear damage was found on the surface of the opening. In contrast, results of heater test using damaged specimen revealed that fractures tended to initiate on the surface of the opening and no obvious further spalling was identified. These experimental findings are consistent with the field observations from the in situ single hole heating damage test.
