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See detailPermeability evolution and water transfer in the excavation damaged zone of a ventilated gallery
Pardoen, Benoît ULg; Talandier, Jean; Collin, Frédéric ULg

in International Journal of Rock Mechanics & Mining Sciences (2016), 85

The fluid transfers occurring around underground galleries are of paramount importance when envisaging the long-term sustainability of underground structures for nuclear waste disposal. These transfers ... [more ▼]

The fluid transfers occurring around underground galleries are of paramount importance when envisaging the long-term sustainability of underground structures for nuclear waste disposal. These transfers are mainly conditioned by the behaviour of the surrounding material and by its interaction with the gallery air. The hydro-mechanical behaviour of the excavation damaged zone, which develops around galleries due to the drilling process, is thenceforward critical because it is composed of fractures having a significant irreversible impact on flow characteristics and transfer kinetics. Besides, the material interaction with the gallery air may engender water drainage and desaturation. Thus, a gallery air ventilation experiment, preceded by its excavation, is numerically modelled in an unsaturated argillaceous rock to study its influence on hydraulic transfers. The fractures are numerically represented with shear strain localisation bands by means of a microstructure enriched model including a regularisation method. The impact of fracturing on the transport properties is addressed by associating the intrinsic permeability increase with mechanical deformation which is amplified in the strain localisation discontinuities. Such dependence permits us to reproduce a significant permeability increase of several orders of magnitude in the excavation damaged zone, in agreement with available experimental measurements. After the excavation, the hydraulic transfers are studied through the reproduction of a gallery air ventilation experiment that implies drainage and desaturation of the surrounding rock. These transfers depend on liquid water and water vapour exchanges at gallery wall that are introduced through a non-classical boundary condition. The model prediction successfully captures the drainage and desaturation kinetics of undisturbed and damaged rock. [less ▲]

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See detailModelling of localised gas preferential pathways in claystone
Gerard, Pierre; Harrington, Jon; Charlier, Robert ULg et al

in International Journal of Rock Mechanics & Mining Sciences (2014), 67

A long-term injection gas test on initially saturated claystone samples under isotropic confining pressure is modelled in a 2D hydro-mechanical framework, which includes the hydraulic anisotropy ... [more ▼]

A long-term injection gas test on initially saturated claystone samples under isotropic confining pressure is modelled in a 2D hydro-mechanical framework, which includes the hydraulic anisotropy. Evidences of localised pathways through the sample have been observed experimentally, which are difficult to reconcile with standard two-phaseflow models. The presence of an embedded pre-existing fracture is included in a continuum finite element model. A hydro-mechanical coupling between the fracture aperture, permeability and the retention properties along the fracture is included in the model. Due to the increase in permeability and the decrease of the air entry pressure induced by the rise in fluid pressure at constant mean total stress, the model provides good agreement with the experimental observations. The discussion offers additional insight into thefluidflow mechanisms into the sample and the processes involved in the development of localised gas pathways. This study allows conclusions to be drawn regarding the performance of the model and its practical limitations. [less ▲]

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See detailHydro-mechanical modelling of the Excavation Damaged Zone around an underground excavation at Mont Terri Rock Laboratory
Levasseur, Séverine ULg; Charlier, Robert ULg; Frieg, Bernd et al

in International Journal of Rock Mechanics & Mining Sciences (2010), 47(3), 414-425

A zone with significant irreversible deformations and significant changes in flow and transport properties is expected to be formed in indurated clay around underground excavations. The stress ... [more ▼]

A zone with significant irreversible deformations and significant changes in flow and transport properties is expected to be formed in indurated clay around underground excavations. The stress perturbation around the excavation could lead to a significant increase of the permeability, related to diffuse and/or localized crack propagation in the material. The main objective of the study is to model these processes at large scale in order to assess their impacts on the performance of radioactive waste geological repositories. This paper concerns more particularly the hydro-mechanical modelling of a long term dilatometer experiment performed in Mont Terri Rock Laboratory in Switzerland within the Selfrac Project. The proposed model defines the permeability as a function of the aperture of the cracks that are generated during the excavation. With this model, the permeability tensor becomes anisotropic. Advantages and drawbacks of this approach are described thanks to the results of the Selfrac long term dilatometer experiment. [less ▲]

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