2013:35 Technical Note, Rock Mechanics – Confidence of SKB’s models for predicting the occurrence of a damage zone around the excavations – Main Review Phase

This assignment, performed at Southwest Research Institute, focusses on evaluating SKB’s assessment of potential occurrence of damaged rock zones (also referred to as excavation-damaged zone or EDZ) around underground excavations at the site. This report presents the authors’ evaluation of SKB’s assessment in the specific area based on questions raised by SSM. The evaluation includes independent calculations by the authors using alternative models and codes to assess potential EDZ configurations and spatial persistence. The independent calculations consider the effects of stress change due to excavation, thermal and glacial loadings, buffer swelling and groundwater pressure.

SKB assessed potential EDZ occurrence due to construction and the stress effects of excavation, thermal loading, glacially induced loading and pore pressure. Based on the assessment, SKB, in its modelling of near-field flow and radionuclide transport, includes a 30-cm thick EDZ at the floor of the deposition tunnel.  SKB assigns the EDZ a tunnel-parallel transmissivity of 10-8 m2/s to assess potential effects of rock damage on safety functions. For deposition holes, SKB does not include an explicit EDZ but accounts for potential damage due to spalling by modifying the flow pathways at the wall of the deposition hole.