Coupled thermo-mechanical simulations for HLW disposal tunnel using distinct element method

In this study, the thermal calculation algorism was developed and introduced to the original distinct element code, and the coupled thermo-mechanical behavior of rock mass around the HLW disposal tunnel was simulated. The simulation results were compared with the experimental data obtained from the pillar stability experiments with mechanical loading and heating at Aspo HRL (hard rock underground laboratory), Sweden. For the simulation, input microscopic parameters were calibrated to match the macroscopic properties of the Aspo Diorite. As a result, the crack propagation process, temperature change and displacement at measuring point during thermal evolution were successfully simulated and calculated results agreed qualitatively well with the measuring and observation results at the site. After the confining pressures were applied, microcracks were generated around the borehole. All microcracks were generated by tensile failure, and the direction of the crack propagation was parallel to the borehole surface. These microcracks were gradually propagated with increasing temperature during heating process. However, the number of microcracks was a few and exfoliation of rock surfaces observed in the in-situ experiment was not formed in the simulation even though the calculated maximum temperature was higher than the experimental data. Therefore, for further improvement of quantitative accuracy, different bonding parameters as a function of thermal aspect will be required. Moreover, calibration of laboratory experiments considering heat should be conducted to investigate the effect of heat on the microscopic parameters to develop more realistic DEM models with bonded particles. (author)