Correcting Errors Using the Framework of Argumentation: Towards Generating Argumentative Correction Propositions from Error Annotation Schemas

PACLIC 23 / City University of Hong Kong / 3-5 December 200

Modeling of Excavation Damaged Zone through the strain localization approach in Boom clay

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Coupled modeling of Excavation Damaged Zone in Boom clay: Strain localization in rock and distribution of contact pressure on the gallery’s lining

Around galleries excavated at depth in geological media, the creation of a damaged zone with significant irreversible deformation is generally unavoidable. In the case of a geological disposal system for high-level radioactive waste, the resulting change in the host rock properties in this damaged zone may potentially be important with respect to the long-term evolution and the performance of that system. In this context, predicting the extent of the so-called Excavation Damaged Zone (EDZ) and, possibly, the fractures' network topology remains a challenge. This study is aimed to simulate numerically the extension of this zone at the large scale's excavation, around the Connecting gallery (HADES URL, Mol, Belgium), in Boom clay host rock through analyzing the evolution of strain localization in shear bands mode. To realistically model the involved phenomena, the concrete lining is considered on the gallery wall highlighting its impacts on the evolution of convergence and EDZ around the gallery. The focus of the current paper is made on analyzing the coupled hydro-mechanical behavior of Boom clay host rock during and after the gallery excavation with respect to the evolution of localized shear bands around the gallery. This study is accompanied by the analysis of the contact mechanism on the interface between the clay massive and the lining. The obtained results reveal some interesting features regarding the contact phenomenon relatively to the evolution pattern of shear bands within the clay around the gallery. To assess the reliability of the proposed approach, a discussion on some in-situ observations during the gallery's construction is also performed based on which a good agreement is found between the in-situ evidence and simulated results

A benchmark of the large-scale in-situ PRACLAY Heater test

editorial reviewedDeep geological disposal is widely considered as one of the most sustainable solutions for isolating radioactive waste from the biosphere and ensuring its long-term management. Understanding the thermo-hydro-mechanical (THM) behavior of the host rock is important for the design of geological disposal. In Belgium, a poorly indurated clay named Boom Clay is studied as a potential host rock thanks to its low intrinsic permeability, its excellent self-sealing property and its capability of adsorption of radionuclides. Laboratory tests [1] and former in-situ small and intermediate scale heater tests [2] carried out in the HADES underground research facility (URF) in Mol (Belgium) already showed the strong hydro-mechanical coupled behavior of the host rock. However, the relatively limited size of these tests suffers from the inevitable mechanical disturbance induced by the installation of the heater and a lower accuracy in reproducing the thermal pressurization in the excavation damaged zone (EDZ). A large-scale in-situ heater test PRACLAY [3] (Fig. 1) is thus now conducted in HADES URF to reproduce the thermal impacts in the EDZ and in the near field and to verify at large scale the far field performance. A 2D benchmark, carried out in the framework of the European Joint programme EURAD HITEC [4], is proposed to model the PRACLAY heater test with fully coupled THM finite elements and to investigate the in-situ behavior of the host rock. The geometry of this model is a cross-section of a supported heating gallery and host rock perpendicular to the gallery axis. Only a quarter of the full gallery is modelled thanks to the symmetry of the problem and the boundary conditions. The numerical modelling comprises four primary phases: excavation, waiting, artificial injection, and heating phases, conducted by adjusting boundary conditions of gallery wall and the linner. An extensive monitoring system established around the PRACLAY gallery enables the observation of temperature and pore water pressure changes within the Boom Clay. The comparison between the numerical prediction and in-situ measurement are carried out. The computation is performed with the finite element code LAGAMINE, developed at the University of Liege. The thermal pressurization due to the discrepancy of thermal dilation between solid and fluid phases is well predicted in the EDZ. To well reproduce the evolution of pore water pressure, the dependency of the permeability on the deformation is introduced in the implemented modelling [5]. The small strain stiffness theory based on the HSsmall model is also taken into account [6]. Finally, a good agreement is obtained between the in-situ measurement and the numerical results (Fig. 2). The benchmark provides valuable insights into the THM impact on the host rock and reliable indications of the model capacity

A benchmark of the large-scale in-situ PRACLAY Heater test

editorial reviewedDeep geological disposal is widely considered as one of the most sustainable solutions for isolating radioactive waste from the biosphere and ensuring its long-term management. Understanding the thermo-hydro-mechanical (THM) behavior of the host rock is important for the design of geological disposal. In Belgium, a poorly indurated clay named Boom Clay is studied as a potential host rock thanks to its low intrinsic permeability, its excellent self-sealing property and its capability of adsorption of radionuclides. Laboratory tests [1] and former in-situ small and intermediate scale heater tests [2] carried out in the HADES underground research facility (URF) in Mol (Belgium) already showed the strong hydro-mechanical coupled behavior of the host rock. However, the relatively limited size of these tests suffers from the inevitable mechanical disturbance induced by the installation of the heater and a lower accuracy in reproducing the thermal pressurization in the excavation damaged zone (EDZ). A large-scale in-situ heater test PRACLAY [3] (Fig. 1) is thus now conducted in HADES URF to reproduce the thermal impacts in the EDZ and in the near field and to verify at large scale the far field performance. A 2D benchmark, carried out in the framework of the European Joint programme EURAD HITEC [4], is proposed to model the PRACLAY heater test with fully coupled THM finite elements and to investigate the in-situ behavior of the host rock. The geometry of this model is a cross-section of a supported heating gallery and host rock perpendicular to the gallery axis. Only a quarter of the full gallery is modelled thanks to the symmetry of the problem and the boundary conditions. The numerical modelling comprises four primary phases: excavation, waiting, artificial injection, and heating phases, conducted by adjusting boundary conditions of gallery wall and the linner. An extensive monitoring system established around the PRACLAY gallery enables the observation of temperature and pore water pressure changes within the Boom Clay. The comparison between the numerical prediction and in-situ measurement are carried out. The computation is performed with the finite element code LAGAMINE, developed at the University of Liege. The thermal pressurization due to the discrepancy of thermal dilation between solid and fluid phases is well predicted in the EDZ. To well reproduce the evolution of pore water pressure, the dependency of the permeability on the deformation is introduced in the implemented modelling [5]. The small strain stiffness theory based on the HSsmall model is also taken into account [6]. Finally, a good agreement is obtained between the in-situ measurement and the numerical results (Fig. 2). The benchmark provides valuable insights into the THM impact on the host rock and reliable indications of the model capacity

Thermal effect characterisation in the excavated damaged zone around tunnels for nuclear waste disposal in agilaceous rocks

La solution du stockage des déchets nucléaires de haute activité et de longue durée de vie dans les couches argileuses profondes comporte de nombreuses incertitudes. Pour combler celles-ci de nombreux projets européens sont réalisés de façon à les minimiser. Le projet TIMODAZ (Thermal Impact On the Damaged Zone Around a Radioactive Waste Disposal in Clay Host Rocks) étudie l'influence de la température sur la zone endommagée. Cette zone correspond à une zone soumise à la redistribution des contraintes lors de l'excavation constituant un lieu de développement de micro et macro fractures. Cet endommagement mécanique est complété par un endommagement thermique lors de la pose des canisters qui vont émettre de la chaleur durant des milliers d'années et donc provoquer une augmentation de la température du massif argileux. Cette élévation de température de l'argile peut faire apparaitre des déformations plastiques thermiques de contraction. Cette nouvelle plasticité peut contribuer au développement de la zone endommagée. L'objectif de ce travail est donc de caractériser la zone endommagée autour des tunnels souterrains, construits dans l'Argile de Boom, soumis à des élévations de température induites par les déchets nucléaires. Durant ce travail, une loi de comportement thermo-mécanique est implémentée. Celle-ci se base sur un "modèle à chapeau" étendu à la thermo-plasticité. Ce modèle comprend la combinaison d'un modèle à frottement interne, d'un critère Cam-Clay et d'un critère de rupture à la traction. Ce modèle est étendu à la température et en particulier à la thermo-plasticité en considérant les travaux de Sultan. Les paramètres thermo-hydro-mécaniques de l'Argile de Boom sont identifiés et servent à la modélisation d'expériences de laboratoire et in situ. Ces expériences consistent en outres en un cylindre creux, en l'expérience de chauffage ATLASIII et en l'expérience à grande échelle PRACLAY. Ces trois expériences ont pour objectif d'étudier l'Argile de Boom d'une petite échelle à une plus grande représentative du massif argileux. L'étude du comportement dans la zone élastique et plastique est également prise en compte via ces différentes expériences. Les résultats, avec différentes lois de comportement, montrent que l'influence de la thermo-plasticité est faible mais non négligeable vis-à-vis des déformations déviatoriques engendrées par l'excavation

Application of a new thermo-mechanical model for study of the nuclear waste disposal in clay rocks

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