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Papers by Mohamed Mahjoub

Research paper thumbnail of A hydromechanical approach for anisotropic elasto-viscoplastic geomaterials: Application to underground excavations in sedimentary rocks

Underground Space, 2018

To better describe excavation operations in deep geological formations, several aspects should be... more To better describe excavation operations in deep geological formations, several aspects should be considered, especially the material anisotropy, time-dependent behavior, and hydromechanical coupling. In the present paper, a hydromechanical model based on the framework of continuous porous media was proposed. The mechanical elasto-viscoplastic constitutive model accounted for the material elastic and non-elastic anisotropies, using a transformation between the real transversely isotropic material and a fictitious isotropic material. Considering the hydraulic behavior, the permeability was expressed as a function of the volumetric viscoplastic strain. The model was applied to a case study of two tunnel excavations in an anisotropic rock under an initial anisotropic stress state. The results of the numerical simulations using a finite element code were in good agreement with the field convergence and permeability data.

Research paper thumbnail of Modeling of Anisotropic Damage Due to Hydrogen Production in a Radioactive Waste Disposal

Environmental Geotechnics, 2018

The production of hydrogen due to metallic container corrosion is one of the most critical proble... more The production of hydrogen due to metallic container corrosion is one of the most critical problems related to an underground radioactive waste disposal project. In fact, the increasing hydrogen pressure in the porous network of the host rock may lead to a mechanical damage, and consequently increase the risk of environment contamination. This paper proposes an approach to study this phenomena using a hydromechanical model, which accounts for the hydrogen and water flows, the anisotropic mechanical damage, and the anisotropic damage-induced permeability change. For a given geometry and material characteristics, a parametric study on the quantity of the produced hydrogen was conducted. Namely, the time of the damage initiation and the extent of the damaged zone were considered. A threshold on the produced quantity, below which the host rock was not damaged, was obtained. This value was found to be considerably higher than the estimates obtained by some studies concerning the corrosion reactions, which is encouraging for the repository project reliability.

Research paper thumbnail of Numerical Study of Callovo-Oxfordian Argillite Expansion due to Gas Injection

International Journal of Geomechanics, 2018

An important aspect in an underground radioactive waste disposal project is the characterization ... more An important aspect in an underground radioactive waste disposal project is the characterization of hydrogen production due to steel container corrosion and its migration in the initially water-saturated host rock. For the French repository project, gas injection tests into initially saturated samples of the Callovo-Oxfordian (COx) claystone were conducted to mimic these phenomena. They showed an important expansion of the tested samples. In this paper, a series of hydromechanical simulations were performed, within the framework of two-phase flow in deformable porous media, to explain both hydraulic and mechanical responses of the material in those experiments. The analysis of experimental and numerical results suggested the simultaneous advance of gas and damage fronts through the sample. The increasing gas pressure led to the decay of the material rigidity and, consequently, to the alteration of the hydraulic properties, particularly the permeability. Simultaneously, the mechanical damage caused a significant expansion of the tested COx samples. The good agreement between the experimental and numerical results supported these explanations and should lead, in future works, to a more complete hydromechanical model aiming to simulate the problem of hydrogen production and migration.

Research paper thumbnail of A damage model for transversely isotropic materials

In a nuclear disposal project, the damage of the hosting rock is a capital issue that should be s... more In a nuclear disposal project, the damage of the hosting rock
is a capital issue that should be studied and understood. This problem is even more complex when the studied rock is anisotropic. In
the present paper, a damage model that takes into account both initial and induced anisotropy is introduced using equivalence relations between the real material and a fictitious isotropic one on which we can take all the advantages of the well established isotropic theory. Numerical simulations using a Finite Element Method (FEM) code shows an agreement between the theoretical predictions and the experimental data of Brazilian tests wi
th different orientation angles.

Research paper thumbnail of An approach to model the mechanical behavior of transversely isotropic material

International Journal for Numerical and Analytical Methods in Geomechanics , 2015

The present work proposes an approach to adapt existing isotropic models to transversely isotropi... more The present work proposes an approach to adapt existing isotropic models to transversely isotropic materials. The main idea is to introduce equivalence relations between the real material and a fictitious isotropic one on which one can take all the advantages of the well-established isotropic theory. Two applications of this approach are presented here: a failure criterion and a damage model that takes into account the load-induced anisotropy. In both cases, theoretical predictions are in agreement with the experimental data. In the present paper, the developed approach is applied to sedimentary rock materials; nevertheless, it can be generalized to any material that exhibits transverse isotropy.

Research paper thumbnail of A hydromechanical approach for anisotropic elasto-viscoplastic geomaterials: Application to underground excavations in sedimentary rocks

Underground Space, 2018

To better describe excavation operations in deep geological formations, several aspects should be... more To better describe excavation operations in deep geological formations, several aspects should be considered, especially the material anisotropy, time-dependent behavior, and hydromechanical coupling. In the present paper, a hydromechanical model based on the framework of continuous porous media was proposed. The mechanical elasto-viscoplastic constitutive model accounted for the material elastic and non-elastic anisotropies, using a transformation between the real transversely isotropic material and a fictitious isotropic material. Considering the hydraulic behavior, the permeability was expressed as a function of the volumetric viscoplastic strain. The model was applied to a case study of two tunnel excavations in an anisotropic rock under an initial anisotropic stress state. The results of the numerical simulations using a finite element code were in good agreement with the field convergence and permeability data.

Research paper thumbnail of Modeling of Anisotropic Damage Due to Hydrogen Production in a Radioactive Waste Disposal

Environmental Geotechnics, 2018

The production of hydrogen due to metallic container corrosion is one of the most critical proble... more The production of hydrogen due to metallic container corrosion is one of the most critical problems related to an underground radioactive waste disposal project. In fact, the increasing hydrogen pressure in the porous network of the host rock may lead to a mechanical damage, and consequently increase the risk of environment contamination. This paper proposes an approach to study this phenomena using a hydromechanical model, which accounts for the hydrogen and water flows, the anisotropic mechanical damage, and the anisotropic damage-induced permeability change. For a given geometry and material characteristics, a parametric study on the quantity of the produced hydrogen was conducted. Namely, the time of the damage initiation and the extent of the damaged zone were considered. A threshold on the produced quantity, below which the host rock was not damaged, was obtained. This value was found to be considerably higher than the estimates obtained by some studies concerning the corrosion reactions, which is encouraging for the repository project reliability.

Research paper thumbnail of Numerical Study of Callovo-Oxfordian Argillite Expansion due to Gas Injection

International Journal of Geomechanics, 2018

An important aspect in an underground radioactive waste disposal project is the characterization ... more An important aspect in an underground radioactive waste disposal project is the characterization of hydrogen production due to steel container corrosion and its migration in the initially water-saturated host rock. For the French repository project, gas injection tests into initially saturated samples of the Callovo-Oxfordian (COx) claystone were conducted to mimic these phenomena. They showed an important expansion of the tested samples. In this paper, a series of hydromechanical simulations were performed, within the framework of two-phase flow in deformable porous media, to explain both hydraulic and mechanical responses of the material in those experiments. The analysis of experimental and numerical results suggested the simultaneous advance of gas and damage fronts through the sample. The increasing gas pressure led to the decay of the material rigidity and, consequently, to the alteration of the hydraulic properties, particularly the permeability. Simultaneously, the mechanical damage caused a significant expansion of the tested COx samples. The good agreement between the experimental and numerical results supported these explanations and should lead, in future works, to a more complete hydromechanical model aiming to simulate the problem of hydrogen production and migration.

Research paper thumbnail of A damage model for transversely isotropic materials

In a nuclear disposal project, the damage of the hosting rock is a capital issue that should be s... more In a nuclear disposal project, the damage of the hosting rock
is a capital issue that should be studied and understood. This problem is even more complex when the studied rock is anisotropic. In
the present paper, a damage model that takes into account both initial and induced anisotropy is introduced using equivalence relations between the real material and a fictitious isotropic one on which we can take all the advantages of the well established isotropic theory. Numerical simulations using a Finite Element Method (FEM) code shows an agreement between the theoretical predictions and the experimental data of Brazilian tests wi
th different orientation angles.

Research paper thumbnail of An approach to model the mechanical behavior of transversely isotropic material

International Journal for Numerical and Analytical Methods in Geomechanics , 2015

The present work proposes an approach to adapt existing isotropic models to transversely isotropi... more The present work proposes an approach to adapt existing isotropic models to transversely isotropic materials. The main idea is to introduce equivalence relations between the real material and a fictitious isotropic one on which one can take all the advantages of the well-established isotropic theory. Two applications of this approach are presented here: a failure criterion and a damage model that takes into account the load-induced anisotropy. In both cases, theoretical predictions are in agreement with the experimental data. In the present paper, the developed approach is applied to sedimentary rock materials; nevertheless, it can be generalized to any material that exhibits transverse isotropy.