Denis BRANQUE - Academia.edu (original) (raw)

Papers by Denis BRANQUE

HAL (Le Centre pour la Communication Scientifique Directe), Jun 28, 2022

HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

HAL (Le Centre pour la Communication Scientifique Directe), Jun 28, 2022

Revue Française de Géotechnique

Un exercice de prévision a été organisé dans le cadre du projet de recherche TULIP (TUnneliers et... more Un exercice de prévision a été organisé dans le cadre du projet de recherche TULIP (TUnneliers et Limitation des Impacts sur des Pieux) sur la base d’une expérimentation en vraie grandeur originale réalisée sur la ligne 16 du Grand Paris Express. Cet exercice de modélisation a vu une large mobilisation des acteurs des travaux souterrains (bureaux d’études, entreprises, concepteurs de logiciels géotechniques, universitaires) qui ont confronté leurs approches d’estimation des déplacements induits en surface du terrain, du tassement d’un pieu, et des efforts induits dans le pieu par le passage du tunnelier. La synthèse des hypothèses effectuées entre les différents participants révèle tout d’abord une grande diversité d’approches, tant en termes de choix des caractéristiques géotechniques des terrains à données d’entrée constantes, qu’en termes de procédés de modélisation du tunnelier. La synthèse des résultats des différents modèles et leur comparaison aux résultats expérimentaux révè...

Revue Française de Géotechnique

Étude expérimentale de l'interaction entre les fonds marins et les pipelines flexibles soumis à l... more Étude expérimentale de l'interaction entre les fonds marins et les pipelines flexibles soumis à la houle et aux courants Résume Les pipelines posés sur les fonds marins en position non recouverte sont dans le cas de mer peu profonde soumis à l'action hydrodynamique de la houle et des courants. Ces efforts hydrodynamiques qui tendent à mettre le pipeline en mouvement sont contrebalancés par la réaction du sol. En conséquence, l'étude de la stabilité de ces pipelines requiert une estimation réaliste des efforts en présence. Cet article fait état d'une étude expérimentale en laboratoire visant à quantifier et à analyser l'interaction sol-eau-pipeline sous les effets de la houle. Lors de ces essais, l'action de la houle et des courants sur le pipeline est simulée mécaniquement (modèle physique d'échelle 1). Les variations de grandeurs physiques telles que la hauteur d'enfoncement du pipeline, la résistance horizontale du sol, les pressions d'eau autour du pipeline sont enregistrées et analysées. Différentes natures de chargements du pipeline, par référence à celles rencontrées sur site, sont étudiées. Une méthode analytique d'estimation de la résistance horizontale du sol est proposée.

This article present a hydro-mechanical model that considers separately the kinematics and the me... more This article present a hydro-mechanical model that considers separately the kinematics and the mechanical behavior of each fluid type (eg liquid water, dissolved air , gaseous air) and the solid matrix in quasi saturated soils. Elastic behavior law is adopted for the solid and liquid phases. This new model was finally implemented in the computer code COMSOL Multiphysics. Numerical simulations are used to demonstrate the ability of this model to reproduce a continuous transition of unsaturated to saturated domains. Mots clefs : sols quasi-saturé, modèle hydro mécanique, transition continu

Materials and Structures, 2021

This paper investigates the compaction characteristics of raw earth via a double-faced static com... more This paper investigates the compaction characteristics of raw earth via a double-faced static compaction and the traditional Proctor test (dynamic process). The corresponding compaction energies are estimated for each individual sample, while the matric suctions are measured by a simple method using filter papers. The obtained results allow to draw the following observations and conclusions. Firstly, similar to classic Proctor tests, a family of iso-energy curves (i.e. tests with identical compaction energy) are identified for the set of static compaction tests. With increasing compaction energy, the iso-energy curve shifts leftwards and upwards, leading to a reduction of optimum moisture content and an increase of maximum dry density. Secondly, a new term called the optimum saturation degree ( S r ) opt is introduced, defined as the degree of saturation S r where ( ρ d ) max is obtained for a given value of compaction energy and for a particular compaction method. For a specific earth type, and a given compaction energy, our experimental results indicate this ( S r ) opt value is constant and that, a unique compression curve linking the degree of compaction D c = ρ d /( ρ d ) max to S r −( S r ) opt exists regardless of the compaction method (static compaction, dynamic Proctor etc.) and compaction energy. Thirdly, the matric suction of specimen subject to static compaction tests is slightly higher than that in dynamic Proctor tests at the same moisture content, whereas the dry density has hardly any correlation with the variation of matric suction. Finally, a new method of earth compaction control is proposed here. This new protocol is organized to compact the earth to a target dry density ρ d , by taking advantage of practically achievable compaction energies and meeting the design requirement, while keeping the S r = ( S r ) opt condition.

E3S Web of Conferences, 2020

Different approaches have been used for modeling retention curves. The experimental correlation w... more Different approaches have been used for modeling retention curves. The experimental correlation was first proposed [1-3]. The physical modelling of unsaturated soils is used for this study. The shape of the retention curve is a consequence of physical assumptions. The paper presents a theoretical model based on elastic spherical particle arrangement. Firstly, a uniform model is presented with a single diameter of soil particle. The second step extends the use of the model to graded soils. The model uses only physical parameters easy to measure. The model is compared with the experimental retention curve of two different samples, the Livet-Gavet loam (1.61m-3mm) as paste and the Gavet sandy loam compacted with 85 falls per layer of Proctor weight. It shows its ability to model the experimental curves. It is of great interest for engineers as it uses only physical parameters. It gives a direct determination of the retention curve along the wetting path and along the drying path. It sh...

Revue Française de Géotechnique, 2020

L’estimation des déplacements induits par le creusement au tunnelier sur des constructions avoisi... more L’estimation des déplacements induits par le creusement au tunnelier sur des constructions avoisinantes (immeubles, ouvrages d’art, tunnels, réseaux…) est une étape essentielle des projets d’ouvrages souterrains en zones urbaines. De cette estimation sont, en effet, déduits ou adaptés des choix forts de conception tels que le tracé du tunnel, le dimensionnement du tunnelier (surcoupe, conicité…) et le choix de ses paramètres de pilotage (pression frontale, pression de bourrage…). Cet article présente des comparaisons entre les résultats de calculs éléments finis 2D et six sections instrumentées d’ouvrages réels. L’ensemble des paramètres nécessaires à la modélisation (modèle géotechnique et paramètres de creusement du tunnelier) est décrit de manière explicite. Ces rétro-analyses permettent de mieux cerner les paramètres clés du problème, en particulier le rôle majeur des pertes de volume induites le long de la jupe du tunnelier.

Computers and Geotechnics, 2020

Applying a high internal pressure inside an underground cavity can increase the extent or intensi... more Applying a high internal pressure inside an underground cavity can increase the extent or intensity of the Excavation Damaged Zone (EDZ). This issue arises in many situations: the geological disposal of radioactive waste where different swelling materials can be encountered (engineered barriers, …), in-situ pressuremeter tests, gas storage projects, etc. This paper presents an analytical approach of the elastoplastic behaviour of a tunnel subjected to a simplified 2-stage loading under the assumption of small strains. In stage-1 (unloading), its excavation is represented in a classical way by cancelling the fictitious internal pressure initially applied to the wall of the future tunnel. In stage-2 (reloading), the internal pressure is increased up to relatively high values. The mechanical behaviour considered is elastic-perfectly-plastic, obeying Tresca's yield criterion and its associated flow rule. In both stages, the elastic phase preceding yielding is considered. During stage-2, the reversed direction of the stress path compared to stage-1 induces reverse yielding, reversing the direction of plastic strain rates. A fully analytical solution is presented, where all field quantities can be assessed by entirely explicit equations. Notably, the critical values of the internal pressure for which yielding resumes, then further extends, are presented.

European Journal of Environmental and Civil Engineering, 2019

This paper proposes a method of describing a global failure in geomechanics problems using the fi... more This paper proposes a method of describing a global failure in geomechanics problems using the finite element method. When considering a quasi-static approach, a limit state cannot be described properly before a numerical divergence of the computation is reached. The main idea is to use a dynamic approach to catch the failure state of a quasi-static problem. However, the events that occur after the failure state are not taken into consideration, because after such a state, the response of a geostructure is not physically and mathematically unique. The second point developed in this paper is the definition of a proper safety factor, which can be useful for engineers. The second-order work criterion under local (homogeneous problems) and global (boundary value problems) forms is reviewed to determine the physical and mathematical interests of using it. Selected finite element simulations are presented. The best way of defining a safety factor using such numerical methods is proposed.

Materials and Structures, 2018

This paper presents a new constitutive model on the poroplastic behaviour of earthen materials ac... more This paper presents a new constitutive model on the poroplastic behaviour of earthen materials accounting for stiffness degradation, using the approach of continuum damage mechanics. The poroplastic behaviour is modelled based on the bounding surface plasticity (BSP) theory and the concept of effective stress while isotropic damage is modelled using a scalar variable. Plastic flow and damage evolution occur simultaneously in a coupled process which take into account the impact of suction. The model was successfully validated against results of triaxial compression tests performed at different relative humidities and confining pressures. Despite the relatively small number of material parameters, this model can reproduce the essential features of earthen materials behaviour observed experimentally: suctioninduced hardening and stiffening, post-peak softening, as well as the progressive transition from contractant to dilatant volumetric behaviour. Use of the BSP theory allows to reproduce a smooth stress-strain relation as experimentally observed, instead of an abrupt change upon plastic yielding predicted by classic elastoplastic models. Furthermore, the present model also furnishes a quantitative description on the degradation of elastic properties hitherto not accounted for, thanks to the additional scalar damage variable. Keywords Unsaturated rammed earth Á Bounding surface plasticity Á Suction Á Damage Á Degradation The original version of this article was revised due to a retrospective Open Access order.

Tunnelling and Underground Space Technology, 2018

This paper brings new elements of understanding on the stress-strain behaviour of soils during tu... more This paper brings new elements of understanding on the stress-strain behaviour of soils during tunnel excavation using earth pressure balance shields (EPBS), thanks to laboratory tests carried out with an original reduced-scale physical model. Typical experiment results obtained during tunnelling with different soil types (purely frictional, cohesive-frictional) and different geometries (homogeneous or stratified grounds) are presented and discussed. These results mainly concern the soil stress-strain behaviour around the tunnel boring machine (TBM) and the soil-machine interaction at ideal rates of excavation. Firstly, results concerning the identification of pertinent control parameters to guarantee the safe advancement of the machine and the ground-supporting function of the cutting wheel are analysed. Surface settlements, stresses and displacements around the tunnel and behind the tunnel face, as well as arching effects around the shield are then presented and discussed.

Materials and Structures, 2019

Computers and Geotechnics, 2019

Near saturation, air bubbles and pockets can be trapped in the porous network of soils. The aim o... more Near saturation, air bubbles and pockets can be trapped in the porous network of soils. The aim of this paper was to present a coupled model that takes into account the effect of this entrapped air on the poro-elasto-plastic behavior of the soil. The model takes into account the physical-mechanical interactions between different phases as well as the kinematics of each constituent (liquid water, dissolved air, gaseous air and solid grains). This new model was implemented in a FEM code. Some numerical simulations were performed to demonstrate its ability to reproduce a continuous transition of unsaturated to saturated states.

Soils and Foundations, 2018

This paper investigates the impact of clay and moisture contents on the shear behavior of compact... more This paper investigates the impact of clay and moisture contents on the shear behavior of compacted earth taking into account loading-unloading cycles. Fine sand was added to a natural soil, thereby obtaining three different soils with clay contents of 35%, 26%, and 17%, respectively. A series of triaxial tests was conducted on samples previously equilibrated at three different values of relative humidity (RH). The evolution of failure strength f c , Young's modulus E, and residual strain e res was investigated according to the clay content and the RH, the last two parameters being measured during the loading-unloading cycles. Firstly, the relative humidity at which the samples were fabricated and conditioned was seen to have a strong impact on the mechanical characteristics of the earthen material. An increase in RH led to a decrease in both failure strength f c and Young's modulus E, and an increase in plastic strain. The tendencies were found to depend on the clay content of the samples. Secondly, with an increasing stress level, a progressive decrease in Young's modulus and an increase in residual strain e res (after a loading-unloading cycle) appeared. Thirdly, within the range of the investigated clay contents, both failure strength f c and residual strain e res increased with an increasing clay content at constant values of RH and confining pressure, the rate of this increase being a function of the RH. Young's modulus E was relatively insensitive to changes in the clay content, its variation being less than 20% for all cases. Finally, based on a particular definition of Bishop's effective stress, involving a specific functional form v(s), the failure states of all the samples were observed to lie approximately on a unique failure line crossing the origin in the (p 0-q) plane regardless of the matric suction and confining pressure.

Journal of Rock Mechanics and Geotechnical Engineering, 2010

HAL (Le Centre pour la Communication Scientifique Directe), Jun 28, 2022

HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

HAL (Le Centre pour la Communication Scientifique Directe), Jun 28, 2022

Revue Française de Géotechnique

Un exercice de prévision a été organisé dans le cadre du projet de recherche TULIP (TUnneliers et... more Un exercice de prévision a été organisé dans le cadre du projet de recherche TULIP (TUnneliers et Limitation des Impacts sur des Pieux) sur la base d’une expérimentation en vraie grandeur originale réalisée sur la ligne 16 du Grand Paris Express. Cet exercice de modélisation a vu une large mobilisation des acteurs des travaux souterrains (bureaux d’études, entreprises, concepteurs de logiciels géotechniques, universitaires) qui ont confronté leurs approches d’estimation des déplacements induits en surface du terrain, du tassement d’un pieu, et des efforts induits dans le pieu par le passage du tunnelier. La synthèse des hypothèses effectuées entre les différents participants révèle tout d’abord une grande diversité d’approches, tant en termes de choix des caractéristiques géotechniques des terrains à données d’entrée constantes, qu’en termes de procédés de modélisation du tunnelier. La synthèse des résultats des différents modèles et leur comparaison aux résultats expérimentaux révè...

Revue Française de Géotechnique

Étude expérimentale de l'interaction entre les fonds marins et les pipelines flexibles soumis à l... more Étude expérimentale de l'interaction entre les fonds marins et les pipelines flexibles soumis à la houle et aux courants Résume Les pipelines posés sur les fonds marins en position non recouverte sont dans le cas de mer peu profonde soumis à l'action hydrodynamique de la houle et des courants. Ces efforts hydrodynamiques qui tendent à mettre le pipeline en mouvement sont contrebalancés par la réaction du sol. En conséquence, l'étude de la stabilité de ces pipelines requiert une estimation réaliste des efforts en présence. Cet article fait état d'une étude expérimentale en laboratoire visant à quantifier et à analyser l'interaction sol-eau-pipeline sous les effets de la houle. Lors de ces essais, l'action de la houle et des courants sur le pipeline est simulée mécaniquement (modèle physique d'échelle 1). Les variations de grandeurs physiques telles que la hauteur d'enfoncement du pipeline, la résistance horizontale du sol, les pressions d'eau autour du pipeline sont enregistrées et analysées. Différentes natures de chargements du pipeline, par référence à celles rencontrées sur site, sont étudiées. Une méthode analytique d'estimation de la résistance horizontale du sol est proposée.

This article present a hydro-mechanical model that considers separately the kinematics and the me... more This article present a hydro-mechanical model that considers separately the kinematics and the mechanical behavior of each fluid type (eg liquid water, dissolved air , gaseous air) and the solid matrix in quasi saturated soils. Elastic behavior law is adopted for the solid and liquid phases. This new model was finally implemented in the computer code COMSOL Multiphysics. Numerical simulations are used to demonstrate the ability of this model to reproduce a continuous transition of unsaturated to saturated domains. Mots clefs : sols quasi-saturé, modèle hydro mécanique, transition continu

Materials and Structures, 2021

This paper investigates the compaction characteristics of raw earth via a double-faced static com... more This paper investigates the compaction characteristics of raw earth via a double-faced static compaction and the traditional Proctor test (dynamic process). The corresponding compaction energies are estimated for each individual sample, while the matric suctions are measured by a simple method using filter papers. The obtained results allow to draw the following observations and conclusions. Firstly, similar to classic Proctor tests, a family of iso-energy curves (i.e. tests with identical compaction energy) are identified for the set of static compaction tests. With increasing compaction energy, the iso-energy curve shifts leftwards and upwards, leading to a reduction of optimum moisture content and an increase of maximum dry density. Secondly, a new term called the optimum saturation degree ( S r ) opt is introduced, defined as the degree of saturation S r where ( ρ d ) max is obtained for a given value of compaction energy and for a particular compaction method. For a specific earth type, and a given compaction energy, our experimental results indicate this ( S r ) opt value is constant and that, a unique compression curve linking the degree of compaction D c = ρ d /( ρ d ) max to S r −( S r ) opt exists regardless of the compaction method (static compaction, dynamic Proctor etc.) and compaction energy. Thirdly, the matric suction of specimen subject to static compaction tests is slightly higher than that in dynamic Proctor tests at the same moisture content, whereas the dry density has hardly any correlation with the variation of matric suction. Finally, a new method of earth compaction control is proposed here. This new protocol is organized to compact the earth to a target dry density ρ d , by taking advantage of practically achievable compaction energies and meeting the design requirement, while keeping the S r = ( S r ) opt condition.

E3S Web of Conferences, 2020

Different approaches have been used for modeling retention curves. The experimental correlation w... more Different approaches have been used for modeling retention curves. The experimental correlation was first proposed [1-3]. The physical modelling of unsaturated soils is used for this study. The shape of the retention curve is a consequence of physical assumptions. The paper presents a theoretical model based on elastic spherical particle arrangement. Firstly, a uniform model is presented with a single diameter of soil particle. The second step extends the use of the model to graded soils. The model uses only physical parameters easy to measure. The model is compared with the experimental retention curve of two different samples, the Livet-Gavet loam (1.61m-3mm) as paste and the Gavet sandy loam compacted with 85 falls per layer of Proctor weight. It shows its ability to model the experimental curves. It is of great interest for engineers as it uses only physical parameters. It gives a direct determination of the retention curve along the wetting path and along the drying path. It sh...

Revue Française de Géotechnique, 2020

L’estimation des déplacements induits par le creusement au tunnelier sur des constructions avoisi... more L’estimation des déplacements induits par le creusement au tunnelier sur des constructions avoisinantes (immeubles, ouvrages d’art, tunnels, réseaux…) est une étape essentielle des projets d’ouvrages souterrains en zones urbaines. De cette estimation sont, en effet, déduits ou adaptés des choix forts de conception tels que le tracé du tunnel, le dimensionnement du tunnelier (surcoupe, conicité…) et le choix de ses paramètres de pilotage (pression frontale, pression de bourrage…). Cet article présente des comparaisons entre les résultats de calculs éléments finis 2D et six sections instrumentées d’ouvrages réels. L’ensemble des paramètres nécessaires à la modélisation (modèle géotechnique et paramètres de creusement du tunnelier) est décrit de manière explicite. Ces rétro-analyses permettent de mieux cerner les paramètres clés du problème, en particulier le rôle majeur des pertes de volume induites le long de la jupe du tunnelier.

Computers and Geotechnics, 2020

Applying a high internal pressure inside an underground cavity can increase the extent or intensi... more Applying a high internal pressure inside an underground cavity can increase the extent or intensity of the Excavation Damaged Zone (EDZ). This issue arises in many situations: the geological disposal of radioactive waste where different swelling materials can be encountered (engineered barriers, …), in-situ pressuremeter tests, gas storage projects, etc. This paper presents an analytical approach of the elastoplastic behaviour of a tunnel subjected to a simplified 2-stage loading under the assumption of small strains. In stage-1 (unloading), its excavation is represented in a classical way by cancelling the fictitious internal pressure initially applied to the wall of the future tunnel. In stage-2 (reloading), the internal pressure is increased up to relatively high values. The mechanical behaviour considered is elastic-perfectly-plastic, obeying Tresca's yield criterion and its associated flow rule. In both stages, the elastic phase preceding yielding is considered. During stage-2, the reversed direction of the stress path compared to stage-1 induces reverse yielding, reversing the direction of plastic strain rates. A fully analytical solution is presented, where all field quantities can be assessed by entirely explicit equations. Notably, the critical values of the internal pressure for which yielding resumes, then further extends, are presented.

European Journal of Environmental and Civil Engineering, 2019

This paper proposes a method of describing a global failure in geomechanics problems using the fi... more This paper proposes a method of describing a global failure in geomechanics problems using the finite element method. When considering a quasi-static approach, a limit state cannot be described properly before a numerical divergence of the computation is reached. The main idea is to use a dynamic approach to catch the failure state of a quasi-static problem. However, the events that occur after the failure state are not taken into consideration, because after such a state, the response of a geostructure is not physically and mathematically unique. The second point developed in this paper is the definition of a proper safety factor, which can be useful for engineers. The second-order work criterion under local (homogeneous problems) and global (boundary value problems) forms is reviewed to determine the physical and mathematical interests of using it. Selected finite element simulations are presented. The best way of defining a safety factor using such numerical methods is proposed.

Materials and Structures, 2018

This paper presents a new constitutive model on the poroplastic behaviour of earthen materials ac... more This paper presents a new constitutive model on the poroplastic behaviour of earthen materials accounting for stiffness degradation, using the approach of continuum damage mechanics. The poroplastic behaviour is modelled based on the bounding surface plasticity (BSP) theory and the concept of effective stress while isotropic damage is modelled using a scalar variable. Plastic flow and damage evolution occur simultaneously in a coupled process which take into account the impact of suction. The model was successfully validated against results of triaxial compression tests performed at different relative humidities and confining pressures. Despite the relatively small number of material parameters, this model can reproduce the essential features of earthen materials behaviour observed experimentally: suctioninduced hardening and stiffening, post-peak softening, as well as the progressive transition from contractant to dilatant volumetric behaviour. Use of the BSP theory allows to reproduce a smooth stress-strain relation as experimentally observed, instead of an abrupt change upon plastic yielding predicted by classic elastoplastic models. Furthermore, the present model also furnishes a quantitative description on the degradation of elastic properties hitherto not accounted for, thanks to the additional scalar damage variable. Keywords Unsaturated rammed earth Á Bounding surface plasticity Á Suction Á Damage Á Degradation The original version of this article was revised due to a retrospective Open Access order.

Tunnelling and Underground Space Technology, 2018

This paper brings new elements of understanding on the stress-strain behaviour of soils during tu... more This paper brings new elements of understanding on the stress-strain behaviour of soils during tunnel excavation using earth pressure balance shields (EPBS), thanks to laboratory tests carried out with an original reduced-scale physical model. Typical experiment results obtained during tunnelling with different soil types (purely frictional, cohesive-frictional) and different geometries (homogeneous or stratified grounds) are presented and discussed. These results mainly concern the soil stress-strain behaviour around the tunnel boring machine (TBM) and the soil-machine interaction at ideal rates of excavation. Firstly, results concerning the identification of pertinent control parameters to guarantee the safe advancement of the machine and the ground-supporting function of the cutting wheel are analysed. Surface settlements, stresses and displacements around the tunnel and behind the tunnel face, as well as arching effects around the shield are then presented and discussed.

Materials and Structures, 2019

Computers and Geotechnics, 2019

Near saturation, air bubbles and pockets can be trapped in the porous network of soils. The aim o... more Near saturation, air bubbles and pockets can be trapped in the porous network of soils. The aim of this paper was to present a coupled model that takes into account the effect of this entrapped air on the poro-elasto-plastic behavior of the soil. The model takes into account the physical-mechanical interactions between different phases as well as the kinematics of each constituent (liquid water, dissolved air, gaseous air and solid grains). This new model was implemented in a FEM code. Some numerical simulations were performed to demonstrate its ability to reproduce a continuous transition of unsaturated to saturated states.

Soils and Foundations, 2018

This paper investigates the impact of clay and moisture contents on the shear behavior of compact... more This paper investigates the impact of clay and moisture contents on the shear behavior of compacted earth taking into account loading-unloading cycles. Fine sand was added to a natural soil, thereby obtaining three different soils with clay contents of 35%, 26%, and 17%, respectively. A series of triaxial tests was conducted on samples previously equilibrated at three different values of relative humidity (RH). The evolution of failure strength f c , Young's modulus E, and residual strain e res was investigated according to the clay content and the RH, the last two parameters being measured during the loading-unloading cycles. Firstly, the relative humidity at which the samples were fabricated and conditioned was seen to have a strong impact on the mechanical characteristics of the earthen material. An increase in RH led to a decrease in both failure strength f c and Young's modulus E, and an increase in plastic strain. The tendencies were found to depend on the clay content of the samples. Secondly, with an increasing stress level, a progressive decrease in Young's modulus and an increase in residual strain e res (after a loading-unloading cycle) appeared. Thirdly, within the range of the investigated clay contents, both failure strength f c and residual strain e res increased with an increasing clay content at constant values of RH and confining pressure, the rate of this increase being a function of the RH. Young's modulus E was relatively insensitive to changes in the clay content, its variation being less than 20% for all cases. Finally, based on a particular definition of Bishop's effective stress, involving a specific functional form v(s), the failure states of all the samples were observed to lie approximately on a unique failure line crossing the origin in the (p 0-q) plane regardless of the matric suction and confining pressure.

Journal of Rock Mechanics and Geotechnical Engineering, 2010