The presented study summarizes results from a numerical simulation campaign in the context of Task B in the DECOVALEX 2011. The project is based on the Äspö Pillar Stability experiment performed by the Swedish Nuclear Fuel and Waste Management Co at Äspö Hard Rock Laboratory. The experimental layout consists of two boreholes in an access tunnel leaving a pillar between them and heaters introduce thermal stresses in addition to the redistributed stresses from the excavations. The main focus was on the design, execution of, and observations during the experiment with particular attention to the yielding strength of the rock mass in the pillar. Based on the findings from the physical field experiments the rock response was simulated using FRACOD. FRACOD is a 2D boundary element software able to simulate the initiation, propagation and coalescence of fractures in geological media. Fracture initiation follows a Mohr-Coulomb criterion and fracture propagation is modeled by a fracture mechanics approach. The simulation campaign successfully back calculated the temperature evolution in the pillar during the heating phase, gave good predictions for the stress development, and gave very good agreement in simulated fracture patterns. The shallow spalling observed in the physical experiment as a result of the thermal heating was explicitly simulated using FRACOD.
The Swedish Nuclear Fuel and Waste Management Company SKB conducted the Äspö Pillar Stability Experiment (APSE) at the Äspö Hard Rock Laboratory. The major objective of the experiment was to determine the spalling/yielding strength of the granitic rock mass and to test how small confining pressures effect the yielding strength. To induce yielding a combination of excavation induced and thermally induced stresses were used in the experiment. The work described in this contribution was conducted within the context of the international DECOVALEX (2011) project.
