Hydro-mechanical coupling under ice sheet conditions : A modelling study of Forsmark

Sammanfattning

The long-term safety of deep geological repositories for spent nuclear fuel dependson understanding how future climate-driven processes may affect host rock characteristics. The advance and retreat of continental ice sheets impose large and variable loads on the subsurface. While Forsmark, Sweden, is a site designated as a nuclear waste repository, the hydro-mechanical effects of glacial loading on its fractured bedrock remain insufficiently quantified. This thesis addresses that gap by analysing how ice sheet loading could alter stress, pore pressure, and permeability conditions in the host rock. Numerical models were developed in COMSOL Multiphysics to simulate coupledfluid flow and rock deformation under glacial loads, based on the geological properties of Forsmark. Both intact and fractured rock scenarios were simulated, allowing comparison of homogeneous and heterogenous responses. Model performance was validated against benchmark problems, Terzaghi’s and Mandel’s consolidation, to ensure reliability. Results show that glacial loading substantially increases stress, displacement, and pore pressure at repository depth. In models that do not account for faults, changes are relatively uniform, whereas models considering fault heterogeneity reveal local drainage effects and irregular pore pressure distributions. These findings indicate that fractures influence hydro-mechanical behaviour significantly under ice sheet loads. Neglecting such processes could therefore underestimate repository response, highlighting their relevance for safety evaluations. This work contributes a modelling framework that can be used for future evaluation of glaciation scenarios in risk assessments of nuclear waste repositories. While uncertainties remain in fault variability, three-dimensional effects, and climate projections, the study establishes a foundation for more comprehensive models that may incorporate thermal, chemical, and inelastic processes. Overall, the thesis emphasizes the necessity of including ice sheet loading in the assessment of long-term safety of nuclear waste storage.