... Zienkiewicz, 1977). The formulation of the problem leads to a non-linear algebraic system whi... more ... Zienkiewicz, 1977). The formulation of the problem leads to a non-linear algebraic system which is solved by a Newton-Raphson Algorithm coupled with a Fixed Point Method (William HP and al., 1986). INTRODUCTION Recent ...
Modelling and Simulation in Materials Science and Engineering, Mar 30, 2010
We explore the possibility that the G2 gas cloud falling in toward SgrA * is the mass-loss envelo... more We explore the possibility that the G2 gas cloud falling in toward SgrA * is the mass-loss envelope of a young T Tauri star. As the star plunges to smaller radius at 1000-6000 km s −1 , a strong bow shock forms where the stellar wind is impacted by the hot X-ray emitting gas in the vicinity of SgrA *. For a stellar mass-loss rate of 4 × 10 −8 M yr −1 and wind velocity 100 km s −1 , the bow shock will have an emission measure (EM = n 2 vol) at a distance ∼10 16 cm, similar to that inferred from the IR emission lines. The ionization of the dense bow shock gas is potentially provided by collisional ionization at the shock front and cooling radiation (X-ray and UV) from the post shock gas. The former would predict a constant line flux as a function of distance from SgrA * , while the latter will have increasing emission at lesser distances. In this model, the star and its mass-loss wind should survive pericenter passage since the wind is likely launched at 0.2 AU and this is much less than the Roche radius at pericenter (∼3 AU for a stellar mass of 2 M). In this model, the emission cloud will probably survive pericenter passage, discriminating this scenario from others.
European Journal of Environmental and Civil Engineering, Jan 28, 2015
In some arid and semi-arid regions, different types of infrastructure assets suffer from degradat... more In some arid and semi-arid regions, different types of infrastructure assets suffer from degradation of the roads, the embankment failures, erosion due to cyclic hydraulic actions and the effects of rainfall infiltration on slopes. Typical cases, such as the national roads in the northwest of Tunisia (Béja city) have been affected dramatically. Recent landslide is manifested in this region, especially in a plastic clay soil. Stability problems are caused by soil saturation and the presence of abundant cracks which are developed after a long dry summer. In fact, due to geotechnical problems, the annual loss due to the damage is estimated at $1 million in Béja area (30 km 2). The effect of rainfall infiltration into the unsaturated clay during wet seasons characterised by either long duration low intensity rain or short duration high intensity rain have been analysed. The elastoplastic Barcelona Basic Model (BBM) has been used and soil movements leading to slope failure were calculated according to the unsaturated state evolution. The effects of cyclic hydraulic paths on the yield function have also been investigated. The yield function evolution depends on the cohesion and the apparent consolidation stress variations. The numerical calculations were evaluated against the field measurement displacements.
Le travail presente concerne l'etude numerique de la stabilite des talus en terre armee a l&#... more Le travail presente concerne l'etude numerique de la stabilite des talus en terre armee a l'aide de la methode cinematique de la theorie de l'analyse limite et le critere de plasticite du materiau homogeneise propose par De Buhan. Deux mises en oeuvre numeriques de la methode cinematique utilisant toutes deux une discretisation du milieu en elements finis sont presentees. La premiere conduit a la resolution d'un probleme d'optimisation lineaire, tandis que, dans la deuxieme, le probleme d'optimisation non lineaire est directement resolu. Les resultats obtenus par ces deux techniques sont ensuite analyses et commentes. (A). (Voir fiche generale DIRR 128861). (Titre en anglais : NUMERICAL FORMULATIONS FOR THE STUDY OF STABILITY IN REINFORCED SOIL WORKS).
International Journal of Innovative Technology and Exploring Engineering, 2019
The aim of this paper is to study the micro-mechanical behavior of an industrial crushable and hi... more The aim of this paper is to study the micro-mechanical behavior of an industrial crushable and highly porous granular material. Lightweight Expanded Clay Aggregates (LECA) was selected in this research for testing thanks to its brittle nature and highly porous character which makes it easier to study the crushable behavior of this material. LECA’s micro-mechanical properties were identified to understand the parameters that affect particle’s crushing. Uniaxial compression tests, consisting on compressing the particles between two rigid platens, were made on a set of single LECA’s particles to investigate the force displacement response and the Hertzian behavior was identified as the contact law. The particles’ strengths were determined for tested granules using the crushing force and grains’ Young moduli were calculated using the suggested contact law. Due to their high variability, the particles’ crushing stress and their Young moduli were related to particle’s dimension using a su...
International Journal of Innovative Technology and Exploring Engineering, 2019
Chemical foam is being used more frequently with Earth Pressure Balance (EPB) shields to achieve ... more Chemical foam is being used more frequently with Earth Pressure Balance (EPB) shields to achieve underground works, which present a rising interest in the excavation technique. During tunneling with an Earth Pressure Balance shield in clayey soil, clogging of the clay occurs, leading to blocking the cutting head and clog then the shield chambers. Surfactants are commonly used as conditioning agents to reduce clay stickiness. This treatment leads to a change in the mechanical properties of conditioned soil. This paper aims tostudy the shear strength behavior of foam-conditioned soil basing on triaxial tests in the undrained consolidated conditions. Experimental results are modeled using the finite element code COMSOL Multiphysics with the aim of analyzing the effect of the percentage of foam on the shear strength behavior. The soil mixture made from 40% of kaolinite and 60% of sand was conditioned with a foaming agent based on anionic surfactant. Consolidated undrained triaxial tests...
European Journal of Environmental and Civil Engineering, 2022
The expected impact of this study is to propose a bio-sourced composite
material coupling mechan... more The expected impact of this study is to propose a bio-sourced composite
material coupling mechanical and hygrothermal performances. This paper
deals with the prediction of hygric properties of compacted raw-earth
material reinforced with the flax fibers. New experiments have been performed on fibers and earth composite specimens. Then two modeling
approaches have been applied using mixing theory and asymptotic homogenization. It was showed, that besides adding flax fibers improves the
mechanical behavior of raw earth as strength and shrinkage reduction,
their impact on the hygric property as water vapor permeability was also
proved. For longitudinal arrangement of flax fibers with different fibers
contents, experimental and modeling results are in good agreement.
Les tunneliers à pressions de terre (EPBM, Earth Pressure Balance Machine) sont conçus pour le cr... more Les tunneliers à pressions de terre (EPBM, Earth Pressure Balance Machine) sont conçus pour le creusement des tunnels en terrain meuble. Dans le cas des sols fins, des additifs sont utilisés pour augmenter les performances et faciliter le creusement. Ces additifs sont classiquement formés par des mousses à base de tensio-actif. Au cours du traitement la mousse s'intègre dans le sol en modifiant sa structure à partir de la création des porosités fermées formées par des bulles de gaz discrètes. La présence de la mousse dans le sol modifie les propriétés hydromécaniques du sol. Cette étude s'intéresse à étudier l'effet d'un agent moussant (CLBF5 TM) sur la perméabilité et la rétention d'eau dans un sol sableux argileux. Des essais de perméabilité à charge variable montrent que l'injection de la mousse dans le sol conduit à la diminution de la perméabilité du mélange. Sous l'effet de la consolidation la perméabilité du sol traité tend vers celle du sol propre...
The study of the clay tensile behaviour is one of the topics which require a specific lighting es... more The study of the clay tensile behaviour is one of the topics which require a specific lighting especially when we give a closely attention to the pathology of the works built with or on the clays submitted to significant tensile strength. Therefore, failure or damage of clay can be related especially to tensile limit and not to shear limit overtaking. It is the case of compacted clay liners in wastes landfill cover or for embankments built on high compressible soils. In order to study the tensile compacted clay behaviour, a series of laboratory bending tests were carried out. On the basis of the test results, different numerical simulations using Discrete Element Method were engaged. Two numerical bending tests were carried out: a three points bending and a four points bending. A comparison between the two numerical protocols is given. Four analytical models (classical elasticity, bimodular elasticity, differential model and struts-tie method) are used in order to interpret bending tests results and are compared with the numerical simulations. At the same time, the validity of the assumptions relative to the four models was discussed. To lead to these results, a study and adjustment of numerical and micromechanical parameters were carried out. It was demonstrated that the Discrete Element Method has a strong correlation with a laboratory tests and can contribute somewhat to the understanding and discussion on the validity degree of the kind of indirect tests and of their interpretation.
The mechanical behavior of granular materials is largely affected by particle breakage. Physical ... more The mechanical behavior of granular materials is largely affected by particle breakage. Physical and mechanical properties of granular materials, such as grain size distribution, deviatoric and volumetric behavior, compressibility and mobilized friction angle are affected by particle crushing. This paper focuses on the evolution of the above mentioned characteristics using the Discrete Element Method (DEM). Behaviors of stiff and soft materials are studied using well established crushing criteria. Results from simulations indicate that stiff materials, have a typical fractal distribution of particle size, which is dominant when confining pressure increases. The fractal characteristic parameter of grain size effect is discussed. Evolution of shear stresses and volumetric strains during shearing are also predicted and analyzed. Expanded perlite, selected as a soft material, is investigated in terms of shear and volumetric behavior. For perlite, triaxial compression tests and corresponding DEM simulations are also performed. Results show good agreement between experiments and simulations and support the fact that the DEM can be considered as a useful tool to predict the behavior of crushable granular materials.
... Zienkiewicz, 1977). The formulation of the problem leads to a non-linear algebraic system whi... more ... Zienkiewicz, 1977). The formulation of the problem leads to a non-linear algebraic system which is solved by a Newton-Raphson Algorithm coupled with a Fixed Point Method (William HP and al., 1986). INTRODUCTION Recent ...
Modelling and Simulation in Materials Science and Engineering, Mar 30, 2010
We explore the possibility that the G2 gas cloud falling in toward SgrA * is the mass-loss envelo... more We explore the possibility that the G2 gas cloud falling in toward SgrA * is the mass-loss envelope of a young T Tauri star. As the star plunges to smaller radius at 1000-6000 km s −1 , a strong bow shock forms where the stellar wind is impacted by the hot X-ray emitting gas in the vicinity of SgrA *. For a stellar mass-loss rate of 4 × 10 −8 M yr −1 and wind velocity 100 km s −1 , the bow shock will have an emission measure (EM = n 2 vol) at a distance ∼10 16 cm, similar to that inferred from the IR emission lines. The ionization of the dense bow shock gas is potentially provided by collisional ionization at the shock front and cooling radiation (X-ray and UV) from the post shock gas. The former would predict a constant line flux as a function of distance from SgrA * , while the latter will have increasing emission at lesser distances. In this model, the star and its mass-loss wind should survive pericenter passage since the wind is likely launched at 0.2 AU and this is much less than the Roche radius at pericenter (∼3 AU for a stellar mass of 2 M). In this model, the emission cloud will probably survive pericenter passage, discriminating this scenario from others.
European Journal of Environmental and Civil Engineering, Jan 28, 2015
In some arid and semi-arid regions, different types of infrastructure assets suffer from degradat... more In some arid and semi-arid regions, different types of infrastructure assets suffer from degradation of the roads, the embankment failures, erosion due to cyclic hydraulic actions and the effects of rainfall infiltration on slopes. Typical cases, such as the national roads in the northwest of Tunisia (Béja city) have been affected dramatically. Recent landslide is manifested in this region, especially in a plastic clay soil. Stability problems are caused by soil saturation and the presence of abundant cracks which are developed after a long dry summer. In fact, due to geotechnical problems, the annual loss due to the damage is estimated at $1 million in Béja area (30 km 2). The effect of rainfall infiltration into the unsaturated clay during wet seasons characterised by either long duration low intensity rain or short duration high intensity rain have been analysed. The elastoplastic Barcelona Basic Model (BBM) has been used and soil movements leading to slope failure were calculated according to the unsaturated state evolution. The effects of cyclic hydraulic paths on the yield function have also been investigated. The yield function evolution depends on the cohesion and the apparent consolidation stress variations. The numerical calculations were evaluated against the field measurement displacements.
Le travail presente concerne l'etude numerique de la stabilite des talus en terre armee a l&#... more Le travail presente concerne l'etude numerique de la stabilite des talus en terre armee a l'aide de la methode cinematique de la theorie de l'analyse limite et le critere de plasticite du materiau homogeneise propose par De Buhan. Deux mises en oeuvre numeriques de la methode cinematique utilisant toutes deux une discretisation du milieu en elements finis sont presentees. La premiere conduit a la resolution d'un probleme d'optimisation lineaire, tandis que, dans la deuxieme, le probleme d'optimisation non lineaire est directement resolu. Les resultats obtenus par ces deux techniques sont ensuite analyses et commentes. (A). (Voir fiche generale DIRR 128861). (Titre en anglais : NUMERICAL FORMULATIONS FOR THE STUDY OF STABILITY IN REINFORCED SOIL WORKS).
International Journal of Innovative Technology and Exploring Engineering, 2019
The aim of this paper is to study the micro-mechanical behavior of an industrial crushable and hi... more The aim of this paper is to study the micro-mechanical behavior of an industrial crushable and highly porous granular material. Lightweight Expanded Clay Aggregates (LECA) was selected in this research for testing thanks to its brittle nature and highly porous character which makes it easier to study the crushable behavior of this material. LECA’s micro-mechanical properties were identified to understand the parameters that affect particle’s crushing. Uniaxial compression tests, consisting on compressing the particles between two rigid platens, were made on a set of single LECA’s particles to investigate the force displacement response and the Hertzian behavior was identified as the contact law. The particles’ strengths were determined for tested granules using the crushing force and grains’ Young moduli were calculated using the suggested contact law. Due to their high variability, the particles’ crushing stress and their Young moduli were related to particle’s dimension using a su...
International Journal of Innovative Technology and Exploring Engineering, 2019
Chemical foam is being used more frequently with Earth Pressure Balance (EPB) shields to achieve ... more Chemical foam is being used more frequently with Earth Pressure Balance (EPB) shields to achieve underground works, which present a rising interest in the excavation technique. During tunneling with an Earth Pressure Balance shield in clayey soil, clogging of the clay occurs, leading to blocking the cutting head and clog then the shield chambers. Surfactants are commonly used as conditioning agents to reduce clay stickiness. This treatment leads to a change in the mechanical properties of conditioned soil. This paper aims tostudy the shear strength behavior of foam-conditioned soil basing on triaxial tests in the undrained consolidated conditions. Experimental results are modeled using the finite element code COMSOL Multiphysics with the aim of analyzing the effect of the percentage of foam on the shear strength behavior. The soil mixture made from 40% of kaolinite and 60% of sand was conditioned with a foaming agent based on anionic surfactant. Consolidated undrained triaxial tests...
European Journal of Environmental and Civil Engineering, 2022
The expected impact of this study is to propose a bio-sourced composite
material coupling mechan... more The expected impact of this study is to propose a bio-sourced composite
material coupling mechanical and hygrothermal performances. This paper
deals with the prediction of hygric properties of compacted raw-earth
material reinforced with the flax fibers. New experiments have been performed on fibers and earth composite specimens. Then two modeling
approaches have been applied using mixing theory and asymptotic homogenization. It was showed, that besides adding flax fibers improves the
mechanical behavior of raw earth as strength and shrinkage reduction,
their impact on the hygric property as water vapor permeability was also
proved. For longitudinal arrangement of flax fibers with different fibers
contents, experimental and modeling results are in good agreement.
Les tunneliers à pressions de terre (EPBM, Earth Pressure Balance Machine) sont conçus pour le cr... more Les tunneliers à pressions de terre (EPBM, Earth Pressure Balance Machine) sont conçus pour le creusement des tunnels en terrain meuble. Dans le cas des sols fins, des additifs sont utilisés pour augmenter les performances et faciliter le creusement. Ces additifs sont classiquement formés par des mousses à base de tensio-actif. Au cours du traitement la mousse s'intègre dans le sol en modifiant sa structure à partir de la création des porosités fermées formées par des bulles de gaz discrètes. La présence de la mousse dans le sol modifie les propriétés hydromécaniques du sol. Cette étude s'intéresse à étudier l'effet d'un agent moussant (CLBF5 TM) sur la perméabilité et la rétention d'eau dans un sol sableux argileux. Des essais de perméabilité à charge variable montrent que l'injection de la mousse dans le sol conduit à la diminution de la perméabilité du mélange. Sous l'effet de la consolidation la perméabilité du sol traité tend vers celle du sol propre...
The study of the clay tensile behaviour is one of the topics which require a specific lighting es... more The study of the clay tensile behaviour is one of the topics which require a specific lighting especially when we give a closely attention to the pathology of the works built with or on the clays submitted to significant tensile strength. Therefore, failure or damage of clay can be related especially to tensile limit and not to shear limit overtaking. It is the case of compacted clay liners in wastes landfill cover or for embankments built on high compressible soils. In order to study the tensile compacted clay behaviour, a series of laboratory bending tests were carried out. On the basis of the test results, different numerical simulations using Discrete Element Method were engaged. Two numerical bending tests were carried out: a three points bending and a four points bending. A comparison between the two numerical protocols is given. Four analytical models (classical elasticity, bimodular elasticity, differential model and struts-tie method) are used in order to interpret bending tests results and are compared with the numerical simulations. At the same time, the validity of the assumptions relative to the four models was discussed. To lead to these results, a study and adjustment of numerical and micromechanical parameters were carried out. It was demonstrated that the Discrete Element Method has a strong correlation with a laboratory tests and can contribute somewhat to the understanding and discussion on the validity degree of the kind of indirect tests and of their interpretation.
The mechanical behavior of granular materials is largely affected by particle breakage. Physical ... more The mechanical behavior of granular materials is largely affected by particle breakage. Physical and mechanical properties of granular materials, such as grain size distribution, deviatoric and volumetric behavior, compressibility and mobilized friction angle are affected by particle crushing. This paper focuses on the evolution of the above mentioned characteristics using the Discrete Element Method (DEM). Behaviors of stiff and soft materials are studied using well established crushing criteria. Results from simulations indicate that stiff materials, have a typical fractal distribution of particle size, which is dominant when confining pressure increases. The fractal characteristic parameter of grain size effect is discussed. Evolution of shear stresses and volumetric strains during shearing are also predicted and analyzed. Expanded perlite, selected as a soft material, is investigated in terms of shear and volumetric behavior. For perlite, triaxial compression tests and corresponding DEM simulations are also performed. Results show good agreement between experiments and simulations and support the fact that the DEM can be considered as a useful tool to predict the behavior of crushable granular materials.
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Papers by Mehrez Jamei
material coupling mechanical and hygrothermal performances. This paper
deals with the prediction of hygric properties of compacted raw-earth
material reinforced with the flax fibers. New experiments have been performed on fibers and earth composite specimens. Then two modeling
approaches have been applied using mixing theory and asymptotic homogenization. It was showed, that besides adding flax fibers improves the
mechanical behavior of raw earth as strength and shrinkage reduction,
their impact on the hygric property as water vapor permeability was also
proved. For longitudinal arrangement of flax fibers with different fibers
contents, experimental and modeling results are in good agreement.
material coupling mechanical and hygrothermal performances. This paper
deals with the prediction of hygric properties of compacted raw-earth
material reinforced with the flax fibers. New experiments have been performed on fibers and earth composite specimens. Then two modeling
approaches have been applied using mixing theory and asymptotic homogenization. It was showed, that besides adding flax fibers improves the
mechanical behavior of raw earth as strength and shrinkage reduction,
their impact on the hygric property as water vapor permeability was also
proved. For longitudinal arrangement of flax fibers with different fibers
contents, experimental and modeling results are in good agreement.