Statistical quantification of earthquake effects on the excavation damage zone

ABSTRACT: Deep geological repositories are being designed to manage spent nuclear fuel of past and future reactors for up to 1 million years across the world. The geosphere surrounding a repository should be structurally stable against geological perturbations, such as earthquakes. Previous studies have evaluated earthquake effects on the repository showing that, there is a measured change in excavation damage zone due to a low probability earthquake event. However, a quantitative study has yet to be performed considering extreme events. In this study, a two-dimensional model was developed in RS2, from Rocscience, a finite element package and compared to a previous repository seismic model. The model utilized a Voronoi joint network around the repository to represent a crystalline rock formation (host rock) and allow for excavation induced damage to evolve during construction. The host rock as well as the engineered barrier system were then subjected to glacial induced stress and earthquake loading. This model was then used to perform a statistical study using analysis of variance (ANOVA) to quantify the earthquake effects. The ANOVA analysis (significance level of 0.05) examined normal and shear stresses and displacements along the Voronoi joints after earthquake events of different seismic coefficients (model coefficients used to represent the peak ground acceleration as a fraction of the acceleration due to gravity), relative to the model with no earthquake events and no glacial loading. Glacial loading caused additional damage in the repository excavation damage zone and had statistically significant effect on joint normal stress. The seismic coefficients had no statistically significant effect on the joint parameters, although only the final state after the earthquake loading was investigated. Future research will examine the dynamic loading response during an earthquake.