A study on damaged zone around an opening in rock-like material due to thermo-mechanical loading

Abstract

The influence of the elevated temperature on the evolution of the EDZ in the rock is an important issue for the safety assessment of radioactive waste repositories. The thermal stress induced additional damage may promote the degradation of mechanical properties of rock mass and increase the extent of the EDZ around the deposition openings which may provide a preferential pathway for radionuclides to migrate.

Biaxial compression tests were performed to investigate the brittle failure around the underground excavations using cubic mortar specimen with a central circular opening. Acoustic emission technique was applied to monitor the failure process around the circular opening. Three failure grades were identified base on the absolute AE energy results. Laboratory heater tests were conducted under confined condition with both intact (undamaged) and damaged cement mortar specimen to study the effect of elevated temperature on the damaged zone. In addition, the effect of damaged zone to the temperature distribution was also investigated in the heater tests.

Numerical simulation was performed using an elastic damage model with the consideration of the heterogeneity of rock-like material to simulate the brittle failure around a circular opening under biaxial compression loading condition. Furthermore, based on the elastic damage model, the coupled thermo-mechanical analysis was implemented to simulate the laboratory heater tests. The validation of the proposed numerical model was achieved by comparison the simulation results with laboratory experimental results.

Furthermore, for evaluating the applicability of the numerical model, numerical simulations were carried out to investigate the thermo-mechanical behaviors at the rock pillar in Äspö pillar stability experiment. The simulation results were agreed well with the simulation results from other numerical codes and the in situ experimental observations. It is believed that the results of this research can contribute to the understanding of coupled thermo-mechanical process in the damaged zone around a circular opening, in the context of deep geological disposal of high-level waste.