Stabilization of clayey soil using fibre reinforcement

The paper presents experimental and numerical investigations on crack evolution during desiccation, on unsaturated, compacted and reinforced clay using natural Alfa fibres. The effect of fibre content is investigated and a comparison between experimental and numerical simulations is made. A modified model for tensile strength is updated in the finite element program CODE_BRIGHT and used to predict tensile cracks induced by desiccation on reinforced soil. The results show that the soil desiccation cracking behaviour is significantly influenced by fibre inclusion and that experimental and numerical results are in good agreement.Postprint (published version

Tensile strength during drying of remoulded and compacted clay: the role of fabric and water retention

The paper presents an experimental investigation on the tensile strength of an unsaturated clay, both in remoulded and compacted states. To complete the experimental study, a new apparatus was designed with the purpose of determining direct tensile stress under controlled-displacement or controlled-force. The design exploits a direct shear test box, which was adapted to the scope of this investigation. Three different hydro-mechanical paths were followed before the tensile strength was determined: a) drying paths on remoulded samples; b) drying paths after compaction at different initial water contents; and c) dynamic compaction at different water contents, hence at different suctions and degrees of saturation. A microstructural investigation was also performed to better understand the experimental results and obtain the most relevant physical parameters. The preparation methods induced different initial fabrics, which dominated the water retention properties, as well as the tensile strength behaviour. A recent model for water retention, including the effects of multimodal fabric, was calibrated on available data and used to predict the suction of the samples along the drying paths, where direct information was not available. A simple model for tensile strength was proposed for its evolution, which included the role of multimodal fabric and their different water storage capabilities, the evolution of dry density and the initial water content (at the beginning of the tensile test path). For the compacted sample, typically showing a multimodal pore size distribution, the tensile strength was found to be a function of the state variables describing the macropore network. Dry density increases on drying appeared in all the cases to dominate the tensile response, Water exchange and suction increase were well correlated to the tensile response evolution.Peer ReviewedPostprint (author's final draft

Numerical simulation of rainfall tests on small-scale slope model

Rainfall-induced landslides are becoming ever more frequent in many regions in the world. In general, the slope failures occur during or immediately after the rainfall. In Tunisia, several regions are concerned by deep or shallow landslides induced by rainwater infiltration, particular in Beja (Tibar). However, due to the high cost of field tests, the quantification of rainwater effects still not adequately clarified. Different small scale slope models were used to study landslide as a result of change in saturation degree. In this paper, we present numerical simulation of rainfall tests on small scale model used clayey soil from a landslide site in Beja, Tibar. The aim of this paper is to study landslide in small scale clayey slope used the same characteristics and conditions of the experimental model realised by Rolando et al. (2004). For this simulation, we will use the numerical approach used to simulate rainfall tests already developed by Rolando et al. (2004). Numerical simulation is conducted using CODE-BRIGHT software

Numerical simulation of rainfall tests on small-scale slope model

Rainfall-induced landslides are becoming ever more frequent in many regions in the world. In general, the slope failures occur during or immediately after the rainfall. In Tunisia, several regions are concerned by deep or shallow landslides induced by rainwater infiltration, particular in Beja (Tibar). However, due to the high cost of field tests, the quantification of rainwater effects still not adequately clarified. Different small scale slope models were used to study landslide as a result of change in saturation degree. In this paper, we present numerical simulation of rainfall tests on small scale model used clayey soil from a landslide site in Beja, Tibar. The aim of this paper is to study landslide in small scale clayey slope used the same characteristics and conditions of the experimental model realised by Rolando et al. (2004). For this simulation, we will use the numerical approach used to simulate rainfall tests already developed by Rolando et al. (2004). Numerical simulation is conducted using CODE-BRIGHT software

Modélisation par éléments discrets de la compressibilité d’un sol sablo-argileux traité par une mousse en cours du temps

International audienceLubricants are used to limit the tunneling shield's impact with the soil, also to facilitate the extraction of excavated soil. In this study, we are interested in the technique adopted by earth pressure tunneling machines (EPB) where surfactant foaming agents are used. Excavated soil is generally classified as waste and stored in the disposal area. The mastery of the physicochemical and mechanical evolution of these wastes makes it possible to explore methods of valorization.The aim of this study is to numerically model a granular medium using the Discret Element Method DEM method in order to study the compressibility of soil-foam mixtures during their evolution over time at the grain scale. The foaming agent is in the form of surfactant bubbles, thus constituting a second granular medium which mixed with that of the soil aggregates. The rigidities of the grains were deduced from the triaxial tests. The modeling is carried out for results oedometric tests. A difference of 14%between experimental and numerical values was founded. Furthermore, the model describes the reduction of the compressibility coefficient of the conditioned soil over time to find the coefficient of the unconditioned soil found experimentally.Les lubrifiants sont utilisés pour limiter les frottements du bouclier de tunnelier avec le sol, et faciliter l’extraction des sols à excaver. Les sols excavés sont généralement classés comme déchets et stockés en zone de dépôt. La maitrise de l’évolution physico-chimique et mécanique de ces déchets, permet d’explorer des méthodes de valorisation. Dans cette étude, on s’intéresse aux sols traités par agents moussants à base de tensioactif utilisés dans la technique adoptée par les tunneliers à pression de terre.Cette étude consiste à modéliser numériquement un milieu granulaire moyennant la méthode des éléments discrets (Discret Element Method : DEM) dans le but d’étudier la compressibilité des mélanges sol-mousse durant leur évolution au cours du temps à l’échelle des grains. L'agent moussant se présente sous forme de bulles de tensioactif, constituant ainsi un deuxième milieu granulaire qui se mélange avec celui des granulats du sol. Les rigidités des grains ont été déduites d’essais triaxiaux. La modélisation est réalisée pour des résultats issus d'essais œdométriques.Une différence de 14 % entre les valeurs expérimentales et numériques est constatée. Par ailleurs, le modèle décrit la diminution du coefficient de compressibilité au cours du temps pour retrouver celle du sol non traité, trouvée expérimentalement

Comportement des systèmes sols/géosynthétiques en couverture decentres de stockage de déchets

International audienceLe stockage de surface des déchets solides non ra-dioactifs (déchets ménagers et déchets industriels banals en centres de stockage de classe 2, déchets industriels spéciaux en centres de stockage de classe 1) suit une réglementation stricte, même s'il vient d'être décidé de surseoir à la loi française de juillet 1992 – loi qui limitait le stockage aux déchets ulti-mes à partir du 1 er juillet 2002. Les caractéristiques physico-chimiques des déchets stockables ainsi que les caractéristiques des barrières de confinement sé-parant le déchet du milieu extérieur sont fixées ré-glementairement. En revanche, le comportement du-rable des centres de stockage modernes nécessite des recherches pluridisciplinaires, notamment dans le domaine géotechnique. Dans l'exposé ci-dessous, un aperçu des recherches entreprises au Lirigm (uni-quement celles à caractères expérimentales) avec le soutien de l'Ademe, de deux grands industriels ges-tionnaires de ces centres (à savoir Suez-Sita et Onyx-Creed) ainsi qu'un bureau d'étude (EEG-Simecsol) est présenté. Il est important de noter que les résul-tats de ces recherches pourront, dans un deuxième temps, être appliquées aux anciennes décharges non contrôlées et autres « points noirs » – on en compte aujourd'hui plus de 8000 en France – qui constituent à long terme un véritable péril pour l'environnement. Une collaboration avec les pays du Maghreb est aussi étudiée, pour y appliquer le savoir faire acquis, et aussi pour y initier des recherches sur ce thème (ENIT, Tunisie). Un centre de stockage de déchets (CSD) est généra-lement constitué d'un tumulus de déchets ceinturé par une barrière de confinement. Le déchet est un matériau macro-hétérogène, souvent très compressi-ble et évolutif dans le cas de matériaux biodégrada-bles. L'identification physique de ces matériaux, préalable à toute étude géomécanique dans le cas des sols, se révèle particulièrement délicate (Thomas, 2000) : éléments particulaires de masse volumique et teneur en eau « constitutive » variables suivant leurs composants, porosité efficace du milieu difficile-ment accessible, etc. Le comportement hydro-mécanique du déchet se révèle donc d'approche beaucoup plus difficile que pour les sols. La per-méabilité en non-saturé conditionne la circulation mixte des lixiviats et des biogaz, donnée importante dans une problématique de bio-réacteur (avec recir-culation des lixiviats). La compressibilité du déchet conditionne les tassements globaux et induit des dé-formations de la barrière de confinement nuisibles à son fonctionnement durable. De plus, la structure composite (sols -géosynthéti-ques) des barrières de confinement induit des pro-blèmes mécaniques spécifiques, en particulier aux interfaces entre déchets, nappes de fond et nappes de couverture de casier

Tensile strength during drying of remoulded and compacted clay: the role of fabric and water retention

The paper presents an experimental investigation on the tensile strength of an unsaturated clay, both in remoulded and compacted states. To complete the experimental study, a new apparatus was designed with the purpose of determining direct tensile stress under controlled-displacement or controlled-force. The design exploits a direct shear test box, which was adapted to the scope of this investigation. Three different hydro-mechanical paths were followed before the tensile strength was determined: a) drying paths on remoulded samples; b) drying paths after compaction at different initial water contents; and c) dynamic compaction at different water contents, hence at different suctions and degrees of saturation. A microstructural investigation was also performed to better understand the experimental results and obtain the most relevant physical parameters. The preparation methods induced different initial fabrics, which dominated the water retention properties, as well as the tensile strength behaviour. A recent model for water retention, including the effects of multimodal fabric, was calibrated on available data and used to predict the suction of the samples along the drying paths, where direct information was not available. A simple model for tensile strength was proposed for its evolution, which included the role of multimodal fabric and their different water storage capabilities, the evolution of dry density and the initial water content (at the beginning of the tensile test path). For the compacted sample, typically showing a multimodal pore size distribution, the tensile strength was found to be a function of the state variables describing the macropore network. Dry density increases on drying appeared in all the cases to dominate the tensile response, Water exchange and suction increase were well correlated to the tensile response evolution.Peer Reviewe

A study of the slope stability in unsaturated swelling marly clay

The analysis of the some experimental field data on the unsaturated unstable slope constituted with a marly clay soil showed that the swelling and collapse phenomena were the origin of the landslide problem. In the studied case, field investigation data and laboratory tests based on the water retention curve determination were analysed. The recorded pore-water pressure field helped us to identify the hydrological conditions. In fact, the wetting and drying cycles involve the total suction and the degree of saturation changes. To predict the shallow slope failure, a constitutive model taking into account the suction effect as well as their dependence on degree of saturation is proposed. It is especially remarkable that the collapse phenomenon is well reproduced when the model incorporates suction changes and saturated preconsolidation stress. The analysis of the slope failure, basing on the field data and the theoretical study, shows the hydraulic and mechanical effects