3D modelling of gas injection tests on FEBEX material: incorporating heterogeneity effects

An experimental programme was conducted as part of the EURAD-GAS project, with the objective of understanding the mechanisms controlling advective gas flow through the Spanish reference barrier material, FEBEX bentonite. The experimental procedure began with the saturation of the material and was followed by a series of gas breakthrough (BT) tests. This paper presents a coupled hydro-mechanical and gas transport (HM-G) model to simulate micro-aperture-driven gas flow through FEBEX bentonite. The modelling framework has been refined using an advanced HM model, incorporating strain-dependent permeability for preferential flow pathways. The parameters of the HM-G model were calibrated through the simulation of laboratory-scale experiments and subsequent back-calculations. The model successfully reproduced the results of gas BT tests, encompassing the processes of saturation, gas injection, gas drainage, re-saturation, and subsequent gas injection. The Barcelona Basic Model was employed as the geo-mechanical model to simulate the development of swelling pressure during the hydration process. The model incorporates randomly distributed permeability zones and heterogeneity in dry density. Key findings from this investigation include the successful simulation of successive gas BT processes that correspond to repository-like conditions, considering a three-dimensional model configuration under an elasto-plastic regime.