A Coupled Hydro-Mechanical Framework for Gas Migration in Bentonite Barrier System for Deep Geological Repositories

Understanding the migration of gas within engineered barrier systems remains essential for evaluating the long-term safety of deep geological repositories (DGRs). This study presents a fully coupled hydro-mechanical (HM) modelling framework developed to examine gas transport in saturated bentonite. A modified formulation for intrinsic permeability evolution is introduced to better represent the mechanical response of bentonite during gas-induced fracturing. The approach employs an exponential law to capture the progressive transition of permeability during stress redistribution. The formulation explicitly incorporates the differential stress variable (σ-p_g), enabling assessment of the combined influence of total stress variation and gas pressure on fracture initiation. Heterogeneity in dry density is represented through a spatially random distribution concept. Allowing simulation of realistic mechanical variability within compacted bentonite blocks. Model predictions are validated against laboratory experiments conducted under different HM boundary conditions. The numerical results reproduce the observed evolution of total stress, pore pressure, and gas breakthrough behaviour. This demonstrates the model’s capability to capture key coupled processes associated with gas migration in bentonite-based barrier materials.