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Pillar Stability Experiment by the coupled T-H-M analysis using the damage modelChijimatsu, Masakazu*; Koyama, Tomofumi*; Kobayashi, Akira*; Shimizu, Hiroyuki*; Nakama, Shigeo
Proceedings of 4th International Conference on Coupled T-H-M-C Processes in Geosystems: Fundamentals, Modeling, Experiments and Applications (GeoProc 2011) (CD-ROM), 13 Pages, 2011/07
The experiment was performed at the sp Hard Rock Laboratory facility owned by the Swedish Nuclear Fuel and Waste Management Co. For the experiment an oval shape tunnel was excavated in which two large holes, 
1.75 m and depth 6.5 m, were excavated. The holes were placed so that a 1 m wide vertical pillar was created between them. The pillar volume was then heated to increase the tangential stress so that yielding could propagate along the borehole wall. Analysis of the coupled thermal, hydraulic and mechanical processes is carried out with the computer code named THAMES. In order to evaluate the spalling phenomena, the damage model was included in the computer code. In the damage mechanics, the change in mechanical behavior due to the growth of damage (cracks) in material is considered. The parameters of this damage model were determined by the unconfined compression test. When the parameters determined by laboratory test were used, the damage did not occur. This is because the parameters were determined from the experiment of the rock core, and it is thought that the parameter of actual bedrock is inferior to that of the rock core. Therefore, the calibration of the damage parameters was performed. When the calibrated parameters were used, simulation results agree qualitatively well with the experimental results. During the simulation of excavation, generating of damage is seen to similar to the observation by the in-situ experiment. Furthermore, temperature change during heating after the excavation of borehole also shows the good agreement between the measured and simulated results. Therefore, it can be said that the spalling phenomenon is expressible even by the application with the continuum model by the use of the suitable parameters.
sp Pillar Stability Experiment; Continuum and discontinuum based approachesKoyama, Tomofumi*; Shimizu, Hiroyuki*; Chijimatsu, Masakazu*; Kobayashi, Akira*; Nakama, Shigeo; Fujita, Tomoo
Proceedings of 4th International Conference on Coupled T-H-M-C Processes in Geosystems: Fundamentals, Modeling, Experiments and Applications (GeoProc 2011) (CD-ROM), 11 Pages, 2011/07
In this paper, the coupled thermal-mechanical processes in the pillar stability experiments carried out at the sp Hard Rock Laboratory by the Swedish Nuclear Fuel and Waste Management Company (SKB) were simulated using both Finite Element Method (FEM) and Distinct Element Method (DEM) with particles. The main purpose for in-situ experiment is to investigate the yielding strength of crystalline rock and the formation and growth of the excavation disturbed/damaged zone (EDZ) during excavation and heating processes. For the 3-D numerical simulations using FEM (called THAMES), the measured in-situ stress and its time evolutions (stress re-distribution) due to the tunnel and two borehole excavations, pressurize in one of the borehole as well as heating process were considered. On the other hand, in 2-D 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 (spalling phenomena). The microscopic parameters used in the DEM simulations were determined by the calibration using the laboratory uniaxial/triaxial compression testing results. The calculation results such as stress distribution, displacements as well as temperature distribution were compared with the in-situ observation and measurements. The simulation results from 3-D FEM shows good agreement with the data obtained from the measurements. The simulated crack propagation during the excavation, pressurizing and heating processes by DEM with particles agrees qualitatively well with the observation. The findings obtained from two different types of numerical simulations can be used for the performance and safety assessment of nuclear waste disposal.