Élaboration et implémentation d'un protocole de laboratoire pour l'étude du potentiel de liquéfaction de résidus miniers

RÉSUMÉ Dans le cadre de l’exploitation minière, différents types de rejets solides sont produits dont les parties les plus importantes se composent des roches stériles et des rejets de concentrateur (résidus miniers). Ces derniers présentent une granulométrie fine et sont entreposés dans des parcs à résidus miniers sous la forme d’une pulpe. En cas de sollicitations cycliques (telles celles engendrées lors d’un séisme), ce type de rejets est particulièrement susceptible à la liquéfaction. Dans ce cas, il peut y avoir des risques conséquents pour les éléments de retenue du parc à résidus (pouvant eux même être édifiés avec des résidus) et donc, pour l’environnement et les populations avoisinantes. Les résidus de mine en roches dures, telles que celles que l’on rencontre en Abitibi, possèdent des propriétés qui les rendent susceptibles à la liquéfaction. La saturation complète, le faible indice de densité, l’abondance des particules silteuse et l’absence de cohésion en sont les principales. En raison de la saturation et du caractère lâche et contractant de ces résidus, les sollicitations dynamiques peuvent engendrer une augmentation des pressions interstitielles conduisant à une diminution des contraintes effectives. Cette diminution des contraintes effectives peut alors conduire à la liquéfaction (associée à une baisse de rigidité et de résistance)du matériau ce qui tend à augmenter les contraintes appliquées sur les digues, ceci pouvant conduire à leur rupture. Dans le cadre de cette problématique, il est nécessaire de pouvoir déterminer le potentiel de liquéfaction des résidus à partir de différents essais. Cette recherche vise à élaborer et implémenter un protocole de laboratoire, basé sur des essais en cellule triaxiale, permettant la caractérisation du comportement des résidus sous chargement cyclique. Le protocole inclut une méthode de préparation des échantillons avec une saturation complète du matériau, tout en évitant l’application d’une contrepression qui peut avoir une influence sur la résistance cyclique des résidus. Le programme expérimental comporte un total de 8 essais quasi-statiques et 17 essais cycliques sur un sable fin en provenance des carrières Demers (Terrebonne, Québec) et sur des résidus miniers Osisko (Malartic, Abitibi, Québec).----------ABASTRACT Mining and ore processing produce different types of waste with the most important being waste rock and tailings. The waste product of mineral processing, tailings, consist of very fine grained material in the form of slurry that is placed in impoundments retained by dikes or dams for indefinite storage. In the event of dynamic loading (such as that engendered by seismic activity) tailings are particularly susceptible to liquefaction. Tailings liquefaction presents risks to the retaining structures, which may actually be composed of tailings, and thus risks to the downstream population and environment. Tailings from hard rock, such as encountered in the Abitibi region of Quebec, possess numerous properties that make them susceptible to liquefaction. They tend to be fully saturated, have low density indices and composed of silt-sized particles without cohesion. Due to their saturation and tendency to contract under shear loading, dynamic loadings may result in the development of excess porewater pressures and a resulting decrease in the effective stress. This decrease in the effective stress could result in liquefaction of the material and an increase in the stresses applied to the retention structure. These additional stresses combined with the additional horizontal loading of the earthquake, have resulted in the failure of tailings impoundments. In the evaluation of the potential for liquefaction induced impoundment failure, it is necessary to determine the potential for tailings liquefaction under seismic loading. The objective of this research was the elaboration and implementation of a laboratory protocol for cyclic triaxial testing for the characterization of the dynamic behavior of tailings. The protocol includes a method of specimen preparation that permits complete saturation of the specimen without the use of backpressure that has been shown to significantly influence dynamic behavior during laboratory testing. The experimental program consisted of 8 quasi-static triaxial and 17 cyclic triaxial tests on fine-grained sand from the Demers Quarry (Terrebonne, Quebec) and on tailings from the Canadian Malartic Mine (Abitibi, Quebec)

Desiccation crack in lime-treated silty clay: Experimental evaluation and constitutive interpretation

peer reviewedThe present work investigates the desiccation effects on a lime-treated clayey silt. Original experimental techniques have been developed to control suction conditions (with osmotic technique) and to track volume variations and cracks occurrence upon drying. Free and constrained dryings are performed to evaluate the shrinkage potential (for free drying) and the conditions of desiccation crack triggering (upon constrained drying). Also, indirect tensile tests and uniaxial compression tests are carried out to evaluate the strength at various suctions. Those investigations have been performed on natural and lime-treated clayey silt in order to emphasis the role of the lime treatment in the triggering and/or mitigation of the cracking process. At the end, generalized effective stress framework with an effective stress parameter calibrated according to a power law is used to provide a constitutive interpretation of the occurrence of desiccation cracks in relation with the water retention properties, the soil stiffness, the tensile strength and the geometrical constraints of the soil samples. For the used compacted materials, it is demonstrated that the lime treatment postpones the occurrence of desiccation cracks and so, plays a favourable role in the stabilization of soft soils subject to drying

Analyse de gazouillis en ligne

National audienceLes tweets échangés sur Internet constituent une source d'information importante même si leurs caractéristiques les rendent difficiles à analyser (140 caractères au maximum, notations abrégées, . . .). Dans cet article, nous définissons un modèle d'entrepôt de données permettant de valoriser et d'analyser de gros volumes de tweets en proposant des mesures pertinentes dans un contexte de découverte de connaissances. L'utilisation des entrepôts de données comme outil de stockage et d'analyse de documents textuels n'est pas nouvelle mais les mesures ne sont pas adaptées aux spécificités des données manipulées. Les résultats des expérimentations sur des données réelles soulignent la pertinence de notre proposition. / Exchanged tweets on the Internet are an important information source, even if their characteristics make them difficult to analyze (a maximum of 140 characters, shorthand notations, ...). In this paper, we define a model of data warehouse to develop and analyze large volumes of tweets by proposing relevant measures in a knowledge discovery context. Using data warehouses in order to store and analyze textual documents is not new. Traditionally they adapt classical measures which are not really adapted to the data specificities. Furthermore we propose that, if a hierarchy is available, we can automatically detect the context. Conducted experiments on real data show the relevance of our approach

Towards an On-Line Analysis of Tweets Processing

International audienceTweets exchanged over the Internet represent an important source of information, even if their characteristics make them dicult to analyze (a maximum of 140 characters, etc.). In this paper, we define a data warehouse model to analyze large volumes of tweets by proposing measures relevant in the context of knowledge discovery. The use of data warehouses as a tool for the storage and analysis of textual documents is not new but current measures are not well-suited to the specificities of the manipulated data. We also propose a new way for extracting the context of a concept in a hierarchy. Experiments carried out on real data underline the relevance of our proposal

An effective stress constitutive framework for the prediction of desiccation crack in lime-treated soil: Experimental characterization and constitutive prediction

peer reviewedThe present work investigates the desiccation effects on a lime-treated silty clay. Original experimental techniques have been developed to control suction conditions (with osmotic technique), to track volume variations and cracks occurrence upon drying. Free and constrained desiccations are performed to evaluate the shrinkage potential (for free drying) and the conditions of desiccation crack triggering (upon constrained drying). Also, indirect tensile tests and uniaxial compression tests are carried out to evaluate the strength and stiffness at various suctions. Those investigations have been performed on natural and lime-treated compacted silty clay in order to emphasize the benefits of the lime treatment in the triggering and/or mitigation of the cracking process. To simulate the field conditions of compaction and obtain specimens having geomechanical properties as close as possible of the real material on site, the particular kneading compaction process in a CBR mould was used, and the final specimens were cut at required sizes with a milling machine numerically controlled by computer (CNC). At the end, generalized effective stress framework with an effective stress parameter χ calibrated according to a power law is used to provide a constitutive interpretation of the occurrence of desiccation cracks in relation with the water retention properties, the soil stiffness, the tensile strength and the geometrical constraints of the soil specimens. It is observed that the cracks initiate under positive (compressive) effective stress. For the used compacted materials, it is demonstrated that the lime treatment postpones the occurrence of desiccation cracks, that are triggered at higher suctions. So, lime treatment plays a favourable role in the reduction of shrinkage and crack occurrence of soft soils subject to drying

TIGER : Interrogation d'une table relationnelle par extension de critères

National audienceAujourd'hui, le web offre une sorte de place publique o` u les sites marchands prolifèrent. Dans un contexte extrêmement concurrentiel, il est capital pour un site de retenir un utilisateur lorsqu'il effectue une recherche. Parmi les stratégies possibles pour atteindre cet objectif, offriràoffrir`offrirà l'utilisateur un outil de recherche flexible est un axe intéressantintéressantàintéressantàétudier. A l'heure actuelle, les formulaires présents sur les sites marchands interprètent demanì ere stricte les critères saisis. Proposer une gestion plus flexible de ces critères permettrait de diminuer le nombre de requêtes formulées et améliorerait donc la qualité de la recherche. Nous proposons, TIGER,une méthode pour une prise en compte flexible des critères utilisateurs. Ainsi, si les critères sont trop contraignants, nous proposons ` a l'utilisateur une combinaison d'extensions de ses critères qui maximise la qualité du résultat tout en minimisant la distancè a la requête d'origine. Les expérimentations menées permettent de valider la qualité des résultats obtenus

How to Extract Relevant Knowledge from Tweets?

[Departement_IRSTEA]Territoires [TR1_IRSTEA]SYNERGIE [Axe_IRSTEA]TETIS-SISOInternational audienceTweets exchanged over the Internet are an important source of information even if their characteristics make them difficult to analyze (e.g., a maximum of 140 characters; noisy data). In this paper, we investigate two different problems. The first one is related to the extraction of representative terms from a set of tweets. More precisely we address the following question: are traditional information retrieval measures appropriate when dealing with tweets?. The second problem is related to the evolution of tweets over time for a set of users. With the development of data mining approaches, lots of very efficient methods have been defined to extract patterns hidden in the huge amount of data available. More recently new spatio-temporal data mining approaches have specifically been defined for dealing with the huge amount of moving object data that can be obtained from the improvement in positioning technology. Due to particularity of tweets, the second question we investigate is the following: are spatio-temporal mining algorithms appropriate for better understanding the behavior of communities over time? These two prob- lems are illustrated through real applications concerning both health and political tweets