IOP Conference Series: Earth and Environmental Science
In the context of nuclear waste management project Cigeo, the behavior of the fractured Callovo O... more In the context of nuclear waste management project Cigeo, the behavior of the fractured Callovo Oxfordian claystone (COx) is studied for its time dependent effect on the long term convergences of the drifts. We present an experimental setup designed to investigate the viscous behavior of a fracture. While few experimental setup already exist with the purpose of studying the time dependent deformation of a rock joint, all of them measure the displacement in the direction of the sheared discontinuities in one point of the sample with devices such as a linear variable displacement transducers (lvdt). The information provided by this sensor comes to measuring the average displacement of the fracture slip. Depending on the configuration of the experimental device, the lvdt sometimes also measures the deformation of the rock medium which cannot always be considered as a rigid body. Which is why we propose in this paper to set a camera up in order to use Digital Image Correlation to get an...
IOP Conference Series: Earth and Environmental Science
The long term behavior of the lining support in deep drifts is a crucial issue for nuclear waste ... more The long term behavior of the lining support in deep drifts is a crucial issue for nuclear waste underground repository project. In order to demonstrate the feasibility of the project, the French Radioactive Waste Management Agency (Andra) has built an Underground Research Laboratory (URL) at Bure. The underground structure is composed of a network of galleries whose drilling generates stress redistribution, damage and fracture in the surrounding medium. The damage and fracturing of this excavation damage zone have a direct effect on the displacement field and on the interaction between the formation and the lining support. The design of the support system request, in order to be as efficient as possible, a precise knowledge of the stress and displacement fields around the drift. For viscoplastic rock formation, the stress field around the drift and its effect on the support system must be determined for at least a couple hundred years. This is why we have studied the long term beha...
This study aims to demonstrate the capability to account for seismic and aseismic responses due t... more This study aims to demonstrate the capability to account for seismic and aseismic responses due to fault reactivation using a cohesive zone model in a Finite Element framework. We adopt an elastic-damage-plastic formulation to predict the fault reactivation while considering unilateral effects observed in geomaterials. In a conceptual 2D problem representing two layers of rock separated by an existing fault, we apply displacement-driven and stress-driven shear loading to provide a first characterization of the instabilities and energy dissipation. Qualitative and quantitative analyses of the dissipative process are provided through the shear stress field and the evolution of the shear stress, displacement, and energy balance. We obtain through the present model the total of dissipated energy thanks to the energy balance. Also, while the elastic energy variation can be positive or negative depending on the type of boundary conditions (stress-driven or displacement-driven), the radiat...
HAL (Le Centre pour la Communication Scientifique Directe), Jun 28, 2022
Le gypse est une roche évaporitique avec une dissolution à l'origine de désordres géotechniques d... more Le gypse est une roche évaporitique avec une dissolution à l'origine de désordres géotechniques dont les propriétés hydromécaniques via la percolation sont peu étudiées malgré la présence d'une porosité intrinsèque au matériau. Cet article présente les caractéristiques microstructurales de 3 gypses aux textures et géologies différentes afin de mieux comprendre les écoulements en leur sein.
HAL (Le Centre pour la Communication Scientifique Directe), May 11, 2021
Oscillations of displacements [2] i = cos(ln) + i sin(ln) ⇒ Interpenetration of crack walls! SIF ... more Oscillations of displacements [2] i = cos(ln) + i sin(ln) ⇒ Interpenetration of crack walls! SIF has "awkwardly complex" physical dimensions [2] =̂î∶ arbitrary reference length [3]
HAL (Le Centre pour la Communication Scientifique Directe), Aug 26, 2019
Nous considérons le problème de deux fissures de longueurs différents, soumises à une contrainte ... more Nous considérons le problème de deux fissures de longueurs différents, soumises à une contrainte uniforme à l'infini, situées à l'interface entre une inclusion circulaire et la matrice infinie. En utilisant la méthode des potentiels complexes de Muskhelishvili, nous obtenons l'expression semi-analytique des facteurs d'intensité de contrainte et du taux restitution d'énergie à l'extrémité des fissures. Finalement,
This work presents numerical simulations of the excavation-induced fractures around galleries in ... more This work presents numerical simulations of the excavation-induced fractures around galleries in Andra Underground Research Laboratory (URL-MHM) in France. An instrumented gallery with geological surveys of the surrounding fractures network was taken as case study. Fractures form a system of distinct, almost parallel discontinuities surrounding the excavation. Finite Element simulations with joint elements (JFEM) constituting the potential fractures were performed to reproduce their spacing and length in the rock. A damage cohesive fracture model representing the stress-displacements behaviour and failure of discontinuities was used. Two configurations were analysed. The first one consists in a JFEM model with a single joints series to analyse the fracture evolution. The second one considers the occurrence of multiple fractures around the gallery. Here, the maximal cracks length approximates correctly the extension of the failure zone observed in-situ. The average radial displacemen...
In sedimentary basin numerous phenomenon depending on the geological time span and its history ca... more In sedimentary basin numerous phenomenon depending on the geological time span and its history can lead to a decrease in effective stress and therefore result in fracture initiation. Thus, during its formation, under certain conditions, natural fracturing and fracture network formation can occur in various context such as under erosion, tectonic loading and the compaction disequilibrium due to significant sedimentation rate.
Geomechanics and Geophysics for Geo-Energy and Geo-Resources, 2021
Fault instability in response to subsurface wastewater injection is controlled by various operati... more Fault instability in response to subsurface wastewater injection is controlled by various operation- and site-dependent parameters. Previous numerical approaches focus on the prediction of the onset of fault reactivation, whereas the subsequent stress redistribution and fault movement are not considered. To better understand the potential correlation between injection activities and fault instability, we develop a hydro-mechanical coupled finite element model and use the May 2012 Timpson earthquake sequence as a case study. Cohesive zone model integrating hyperbolic damage criterion and weakening behaviors is assigned to element interface to represent the nearby fault and capture the resulting fault behaviors under fluid injection. Simulation results indicate that this model is able to reveal the spatiotemporal evolution of pore pressure and geomechanical stress field at the Timpson site. Under continual fluid injection, pore pressure increases and gradually stabilizes, more evident in regions close to the injection layer. Poroelastic stress and pore pressure changes jointly influence the fault stability. Through damage evolution considered in the cohesive zone model, the finite element model can simulate the foreshock and main shock of the Timpson earthquake sequence, associated with fault displacement and stress relaxation. Once the damage criterion is reached, the stress redistribution at the failed fault segment induces further increase of stress on the other domains of the fault, which drives subsequent fault slip. This study brings new insights into the numerical modeling of induced earthquakes and highlights the importance of accounting for fluid injection activities to minimize the potential of fault reactivation and slip.
The viscoplastic behavior of coarse and bimodal fine/ultrafine grained (F/UFG) Al5083 alloy was i... more The viscoplastic behavior of coarse and bimodal fine/ultrafine grained (F/UFG) Al5083 alloy was investigated between 20°C and 200°C through tensile tests at various strain rates, and stress relaxation tests to deduce the strain rate sensitivity (SRS). The plastic strain fields were measured by correlation of SEM images. In the F/UFG material at high temperature, very high strains were measured in shear bands which sometimes crossed the whole gage width and exhibited intensive grain boundary sliding (GBS). Both the SRS and ductility rose with the temperature, and as the strain rate decreased, mainly due to a rising contribution of GBS, which accommodated a much larger fraction of the global strain in the F/UFG material. The boundary between the temperature-strain rate domains where grain refinement led either to strengthening or to softening was determined. Finite element simulations of tension and relaxation tests with viscoplastic grains and sliding grain boundaries captured the macro-scale behavior of the F/UFG material. It also provided some insight into the mechanisms of correlated and cooperative GBS and grain rotation along percolation paths (both inter and intragranular), probably, responsible for macro shear banding.
IOP Conference Series: Earth and Environmental Science
In the context of nuclear waste management project Cigeo, the behavior of the fractured Callovo O... more In the context of nuclear waste management project Cigeo, the behavior of the fractured Callovo Oxfordian claystone (COx) is studied for its time dependent effect on the long term convergences of the drifts. We present an experimental setup designed to investigate the viscous behavior of a fracture. While few experimental setup already exist with the purpose of studying the time dependent deformation of a rock joint, all of them measure the displacement in the direction of the sheared discontinuities in one point of the sample with devices such as a linear variable displacement transducers (lvdt). The information provided by this sensor comes to measuring the average displacement of the fracture slip. Depending on the configuration of the experimental device, the lvdt sometimes also measures the deformation of the rock medium which cannot always be considered as a rigid body. Which is why we propose in this paper to set a camera up in order to use Digital Image Correlation to get an...
IOP Conference Series: Earth and Environmental Science
The long term behavior of the lining support in deep drifts is a crucial issue for nuclear waste ... more The long term behavior of the lining support in deep drifts is a crucial issue for nuclear waste underground repository project. In order to demonstrate the feasibility of the project, the French Radioactive Waste Management Agency (Andra) has built an Underground Research Laboratory (URL) at Bure. The underground structure is composed of a network of galleries whose drilling generates stress redistribution, damage and fracture in the surrounding medium. The damage and fracturing of this excavation damage zone have a direct effect on the displacement field and on the interaction between the formation and the lining support. The design of the support system request, in order to be as efficient as possible, a precise knowledge of the stress and displacement fields around the drift. For viscoplastic rock formation, the stress field around the drift and its effect on the support system must be determined for at least a couple hundred years. This is why we have studied the long term beha...
This study aims to demonstrate the capability to account for seismic and aseismic responses due t... more This study aims to demonstrate the capability to account for seismic and aseismic responses due to fault reactivation using a cohesive zone model in a Finite Element framework. We adopt an elastic-damage-plastic formulation to predict the fault reactivation while considering unilateral effects observed in geomaterials. In a conceptual 2D problem representing two layers of rock separated by an existing fault, we apply displacement-driven and stress-driven shear loading to provide a first characterization of the instabilities and energy dissipation. Qualitative and quantitative analyses of the dissipative process are provided through the shear stress field and the evolution of the shear stress, displacement, and energy balance. We obtain through the present model the total of dissipated energy thanks to the energy balance. Also, while the elastic energy variation can be positive or negative depending on the type of boundary conditions (stress-driven or displacement-driven), the radiat...
HAL (Le Centre pour la Communication Scientifique Directe), Jun 28, 2022
Le gypse est une roche évaporitique avec une dissolution à l'origine de désordres géotechniques d... more Le gypse est une roche évaporitique avec une dissolution à l'origine de désordres géotechniques dont les propriétés hydromécaniques via la percolation sont peu étudiées malgré la présence d'une porosité intrinsèque au matériau. Cet article présente les caractéristiques microstructurales de 3 gypses aux textures et géologies différentes afin de mieux comprendre les écoulements en leur sein.
HAL (Le Centre pour la Communication Scientifique Directe), May 11, 2021
Oscillations of displacements [2] i = cos(ln) + i sin(ln) ⇒ Interpenetration of crack walls! SIF ... more Oscillations of displacements [2] i = cos(ln) + i sin(ln) ⇒ Interpenetration of crack walls! SIF has "awkwardly complex" physical dimensions [2] =̂î∶ arbitrary reference length [3]
HAL (Le Centre pour la Communication Scientifique Directe), Aug 26, 2019
Nous considérons le problème de deux fissures de longueurs différents, soumises à une contrainte ... more Nous considérons le problème de deux fissures de longueurs différents, soumises à une contrainte uniforme à l'infini, situées à l'interface entre une inclusion circulaire et la matrice infinie. En utilisant la méthode des potentiels complexes de Muskhelishvili, nous obtenons l'expression semi-analytique des facteurs d'intensité de contrainte et du taux restitution d'énergie à l'extrémité des fissures. Finalement,
This work presents numerical simulations of the excavation-induced fractures around galleries in ... more This work presents numerical simulations of the excavation-induced fractures around galleries in Andra Underground Research Laboratory (URL-MHM) in France. An instrumented gallery with geological surveys of the surrounding fractures network was taken as case study. Fractures form a system of distinct, almost parallel discontinuities surrounding the excavation. Finite Element simulations with joint elements (JFEM) constituting the potential fractures were performed to reproduce their spacing and length in the rock. A damage cohesive fracture model representing the stress-displacements behaviour and failure of discontinuities was used. Two configurations were analysed. The first one consists in a JFEM model with a single joints series to analyse the fracture evolution. The second one considers the occurrence of multiple fractures around the gallery. Here, the maximal cracks length approximates correctly the extension of the failure zone observed in-situ. The average radial displacemen...
In sedimentary basin numerous phenomenon depending on the geological time span and its history ca... more In sedimentary basin numerous phenomenon depending on the geological time span and its history can lead to a decrease in effective stress and therefore result in fracture initiation. Thus, during its formation, under certain conditions, natural fracturing and fracture network formation can occur in various context such as under erosion, tectonic loading and the compaction disequilibrium due to significant sedimentation rate.
Geomechanics and Geophysics for Geo-Energy and Geo-Resources, 2021
Fault instability in response to subsurface wastewater injection is controlled by various operati... more Fault instability in response to subsurface wastewater injection is controlled by various operation- and site-dependent parameters. Previous numerical approaches focus on the prediction of the onset of fault reactivation, whereas the subsequent stress redistribution and fault movement are not considered. To better understand the potential correlation between injection activities and fault instability, we develop a hydro-mechanical coupled finite element model and use the May 2012 Timpson earthquake sequence as a case study. Cohesive zone model integrating hyperbolic damage criterion and weakening behaviors is assigned to element interface to represent the nearby fault and capture the resulting fault behaviors under fluid injection. Simulation results indicate that this model is able to reveal the spatiotemporal evolution of pore pressure and geomechanical stress field at the Timpson site. Under continual fluid injection, pore pressure increases and gradually stabilizes, more evident in regions close to the injection layer. Poroelastic stress and pore pressure changes jointly influence the fault stability. Through damage evolution considered in the cohesive zone model, the finite element model can simulate the foreshock and main shock of the Timpson earthquake sequence, associated with fault displacement and stress relaxation. Once the damage criterion is reached, the stress redistribution at the failed fault segment induces further increase of stress on the other domains of the fault, which drives subsequent fault slip. This study brings new insights into the numerical modeling of induced earthquakes and highlights the importance of accounting for fluid injection activities to minimize the potential of fault reactivation and slip.
The viscoplastic behavior of coarse and bimodal fine/ultrafine grained (F/UFG) Al5083 alloy was i... more The viscoplastic behavior of coarse and bimodal fine/ultrafine grained (F/UFG) Al5083 alloy was investigated between 20°C and 200°C through tensile tests at various strain rates, and stress relaxation tests to deduce the strain rate sensitivity (SRS). The plastic strain fields were measured by correlation of SEM images. In the F/UFG material at high temperature, very high strains were measured in shear bands which sometimes crossed the whole gage width and exhibited intensive grain boundary sliding (GBS). Both the SRS and ductility rose with the temperature, and as the strain rate decreased, mainly due to a rising contribution of GBS, which accommodated a much larger fraction of the global strain in the F/UFG material. The boundary between the temperature-strain rate domains where grain refinement led either to strengthening or to softening was determined. Finite element simulations of tension and relaxation tests with viscoplastic grains and sliding grain boundaries captured the macro-scale behavior of the F/UFG material. It also provided some insight into the mechanisms of correlated and cooperative GBS and grain rotation along percolation paths (both inter and intragranular), probably, responsible for macro shear banding.
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Papers by Amade Pouya