Distinct element approach for the analysis of coupled thermal-mechanical processes in the near field of the HLW repository

Koyama, Tomofumi*; Shimizu, Hiroyuki*; Chijimatsu, Masakazu*; Nakama, Shigeo ; Fujita, Tomoo 

In this paper, the coupled thermal-mechanical processes in the sp pillar stability experiments (APSE) carried out by the Swedish Nuclear Fuel and Waste Management Company (SKB) were simulated using 2 dimensional Distinct Element Method (2-D DEM) with particles. The main objective for large scale in-situ experiment is to investigate the yielding strength of crystalline rock and the formation of the excavation disturbed/damaged zone (EDZ) during excavation of two boreholes, pressurizing in one of the borehole and heating processes. For the simulations, the heat flow algorism was newly introduced into original DEM code to consider heating processes in the APSE. For the DEM simulations, one of the borehole cross sections (in 2-D) was selected and modeled as an assemblage of many particles bonded each other to investigate the failure mechanism during excavation and heating processes in detail including crack propagation at the borehole surface. The microscopic parameters used in the DEM simulations were determined by the calibration using the laboratory uniaxial/triaxial compression testing results. The calculated stress distribution, displacements and temperature distribution were compared with the ones obtained from in-situ measurements and 2-D, 3-D FEM simulations. The simulated crack propagation during the excavation, pressurizing and heating processes by DEM with particles agrees qualitatively well with the observation. The parametric study for initial microcracks was performed to reproduce the spalling phenomena observed in the APSE.