Abstract :
[en] Nowadays, the deep geological disposal based on the multi-barriers confinement concept, is considered as one of the most promising solutions for the safe storage of radioactive wastes. Many Thermo-Hydro-Mechanical (THM) phenomena are likely to occur during the construction and the lifetime of the repository, which could alter the confining function of the different constituent layers.
Among these, the underground excavation process tends to create a so-called Excavation Damaged Zone (EDZ) in the surrounding of the storage galleries, where the mechanical and hydraulic properties are affected. For instance, the hydraulic permeability is increased compared to the sound rock formation. Moreover, during the exploitation of the system, a certain amount of gases, such as hydrogen could actually be generated in the nearfield of the repository due to the anoxic corrosion of the metal components, and lead to the alteration of the host rock behaviour.
In light of this, the present work aims at developing a numerical tool within the finite element code LAGAMINE1, able to reproduce simultaneously the development of strain localisation bands due to excavation, the multiphysical couplings associated with gas generation and migrations, as well as their possible close interactions. This model includes on the one hand a THM part to describe triphasic porous media under unsaturated and non-isothermal conditions. On the other hand, since the problem involving strain localisation is not well posed when modelled using classical mechanics, the local second gradient approach is also integrated to the model. It helps avoiding the pathological mesh dependency by considering an enrichment of the continuum with microstructure effects through a regularizing internal length.
This model is subsequently put into practise for the case of Boom Clay Formation, investigated by the Belgian National Radioactive Waste Management Agency (ONDRAF) to host a deep geological disposal. More particularly, two in situ gas injection tests conducted in two distinct directions in the Underground Research Laboratory (URL) in Mol, are simulated in 2D plane stain state. The modelling finally provides information about the fracture structure and permeability evolution due to the excavation, and about the stress state during a second phase of pore pressures stabilization, and a last phase of gas migrations.
