A previsão do comportamento de resíduos constituiu-se em um desafio geotécnico, uma vez que estes materiais apresentam uma resposta distinta dos materiais usualmente encontrados em depósitos naturais. A análise dos recalques da fundação, decorrentes da sobrecarga imposta pelo alteamento, é complexa, tendo em vista que o adensamento de resíduos pressupõe grandes deformações, invalidando o uso de teorias clássicas de adensamento. Atualmente, no Brasil, a técnica de disposição de resíduos de bauxita prevê uma operação inicial de lançamento no interior de lagos artificiais, em forma de polpa. Após o esgotamento do lago e ressecamento do resíduo, inicia-se o lançamento pelo método a montante. Neste método, a polpa é lançada sobre o resíduo pré-existente, que se encontra em processo de adensamento. O presente trabalho tem como objetivo reproduzir numericamente o comportamento de áreas de resíduos durante a etapa de alteamento a montante. A pesquisa tem como enfoque 2 áreas de resíduos de bauxita. Uma delas encontra-se em fase de reabilitação e dispõe de instrumentação de campo (recalques e deslocamentos horizontais). A outra se encontra em fase de operação do alteamento e dispõe de dados experimentais. Desta forma, a metodologia consistiu na reprodução numérica do processo de alteamento da área instrumentada e comparação dos resultados com a instrumentação de campo, com objetivo de avaliar o modelo numérico e os parâmetros do resíduo. Posteriormente, realizou-se a previsão do comportamento do resíduo de fundação da área em fase de alteamento. Os parâmetros geotécnicos foram definidos a partir de um extenso programa de ensaios de campo e laboratório, executado no local em estudo, fazendo-se uso de um tratamento estatístico dos dados experimentais. Os resultados numéricos mostraram a potencialidade do programa na previsão do comportamento de áreas de resíduos durante o alteamento a montante, com previsões de recalques e deslocamentos horizontais coerentes com a instrumentação de campo. / The prediction of solid wastes behavior is a challenge for geotechnical engineers, since its response differ from the materials usually found in natural deposits. The analysis of the settlements of the foundation, due to the embankment raising is complex. Tailings undergo large settlements, which cannot be evaluated by ordinary consolidation theories. In Brazil, bauxite tailings are initially discharged into impoundment areas in a slurry form. After achieving the storage capacity of the reservoir, the tailing is allowed to dry, in order to enhance its resistance. Subsequently, the embankment is raised by the upstream method, and the mud is discharged on top of a material which is undergoing a consolidation process. The present research aims at reproducing numerically the response of bauxite tailings due to an upstream raising operation. The research focused 2 impoundment areas at same site. One area is being environmentally rehabilitated and is instrumented with vertical and horizontal gauges. The other is still in operation and an experimental investigation was carried out at this site. The methodology consisted of simulating the sequence of embankment raises and comparing the results with field instrumentation, in order to evaluate the numerical model and waste parameters. Subsequently, the behavior of the foundation of the area undergoing a raising embankment operation was evaluated. The geotechnical parameters were defined according to a statistical treatment of results of the experimental program (field and laboratory). The vertical and horizontal displacements, predicted by the numerical simulation, fitted reasonably well with field instrumentation and showed the inherent potential of the numerical modeling.

A previsão do comportamento de resíduos constituiu-se em um desafio geotécnico, uma vez que estes materiais apresentam uma resposta distinta dos materiais usualmente encontrados em depósitos naturais. A análise dos recalques da fundação, decorrentes da sobrecarga imposta pelo alteamento, é complexa, tendo em vista que o adensamento de resíduos pressupõe grandes deformações, invalidando o uso de teorias clássicas de adensamento. Atualmente, no Brasil, a técnica de disposição de resíduos de bauxita prevê uma operação inicial de lançamento no interior de lagos artificiais, em forma de polpa. Após o esgotamento do lago e ressecamento do resíduo, inicia-se o lançamento pelo método a montante. Neste método, a polpa é lançada sobre o resíduo pré-existente, que se encontra em processo de adensamento. O presente trabalho tem como objetivo reproduzir numericamente o comportamento de áreas de resíduos durante a etapa de alteamento a montante. A pesquisa tem como enfoque 2 áreas de resíduos de bauxita. Uma delas encontra-se em fase de reabilitação e dispõe de instrumentação de campo (recalques e deslocamentos horizontais). A outra se encontra em fase de operação do alteamento e dispõe de dados experimentais. Desta forma, a metodologia consistiu na reprodução numérica do processo de alteamento da área instrumentada e comparação dos resultados com a instrumentação de campo, com objetivo de avaliar o modelo numérico e os parâmetros do resíduo. Posteriormente, realizou-se a previsão do comportamento do resíduo de fundação da área em fase de alteamento. Os parâmetros geotécnicos foram definidos a partir de um extenso programa de ensaios de campo e laboratório, executado no local em estudo, fazendo-se uso de um tratamento estatístico dos dados experimentais. Os resultados numéricos mostraram a potencialidade do programa na previsão do comportamento de áreas de resíduos durante o alteamento a montante, com previsões de recalques e deslocamentos horizontais coerentes com a instrumentação de campo. / The prediction of solid wastes behavior is a challenge for geotechnical engineers, since its response differ from the materials usually found in natural deposits. The analysis of the settlements of the foundation, due to the embankment raising is complex. Tailings undergo large settlements, which cannot be evaluated by ordinary consolidation theories. In Brazil, bauxite tailings are initially discharged into impoundment areas in a slurry form. After achieving the storage capacity of the reservoir, the tailing is allowed to dry, in order to enhance its resistance. Subsequently, the embankment is raised by the upstream method, and the mud is discharged on top of a material which is undergoing a consolidation process. The present research aims at reproducing numerically the response of bauxite tailings due to an upstream raising operation. The research focused 2 impoundment areas at same site. One area is being environmentally rehabilitated and is instrumented with vertical and horizontal gauges. The other is still in operation and an experimental investigation was carried out at this site. The methodology consisted of simulating the sequence of embankment raises and comparing the results with field instrumentation, in order to evaluate the numerical model and waste parameters. Subsequently, the behavior of the foundation of the area undergoing a raising embankment operation was evaluated. The geotechnical parameters were defined according to a statistical treatment of results of the experimental program (field and laboratory). The vertical and horizontal displacements, predicted by the numerical simulation, fitted reasonably well with field instrumentation and showed the inherent potential of the numerical modeling.

Résumé : Ce projet de recherche s’inscrit dans le cadre d’une requête de l’entreprise partenaire, Golder Associés Ltée. Cette dernière s’interrogeait sur la consolidation d’un résidu minier épaissi, une approche de plus en plus utilisée dans le domaine de la gestion des aires de déposition des résidus miniers. Ce type de matériau est épaissi jusqu’à un point où une fois déposé, il ne connaît pas ou peu de ségrégation, rejette moins d’eau et possède généralement un angle de repos plus grand que les résidus conventionnels. L’intérêt de cette approche dans le cadre de cette étude consiste en la réduction des empreintes des aires de déposition par la combinaison des résidus épaissis et des rehaussements par l’amont. La consolidation de ce type de résidus a été peu étudiée depuis leur développement. En rassemblant les observations rapportées dans les écrits scientifiques, il est possible de ressortir que le mécanisme physique générant la dissipation des pressions interstitielles en excès et le tassement au moment de la déposition est essentiellement la consolidation sous le poids propre. Un essai en colonne de tassement instrumentée de transmetteurs de pression a permis l’étude de la consolidation sous le poids propre en termes de dissipation des pressions d’eau avec une grande précision. Un essai en consolidomètre a permis de définir la compressibilité du matériau durant cette étape de consolidation sous le poids propre avec une précision acceptable. Les résultats expérimentaux ont été reproduits à l’aide du modèle CS2 suite à quelques ajustements des relations constitutives. CS2 considère la consolidation sous le poids propre et les grandes déformations d’une déposition instantanée. Le rapprochement entre le modèle CS2 et les résultats expérimentaux est sans équivoque et permet de prendre connaissance de certains aspects de la consolidation sous le poids propre qui étaient peu détaillés jusqu'à maintenant dans les écrits scientifiques. L’importance de la consolidation sous le poids propre et son intégration dans le plan de déposition proposé par l’entreprise partenaire a été évaluée à l’aide du logiciel SIGMA/W. Les capacités de ce logiciel ont tout d’abord été étudiées en 1D. Ces vérifications visaient la considération de la consolidation sous le poids propre tout en examinant la formulation de SIGMA/W pour un remplissage progressif. Ces simulations 1D ont pu être comparées aux résultats du modèle CS4, un modèle calqué sur CS2 qui permet un remplissage progressif. Finalement, une campagne de simulation à grande échelle en 2D visant la simulation d’une aire de déposition de résidus épaissis a permis d’examiner les éléments importants dans la considération de ce mécanisme à l’aide du logiciel commercial SIGMA/W. Il en ressort que le logiciel SIGMA/W n’est pas le logiciel idéal pour simuler la déposition progressive de résidus épaissis en considérant la consolidation sous le poids propre et ce pour maintes raisons. Les résultats de cette étude viennent situer l’importance de la consolidation sous le poids propre dans les résidus épaissis et fournissent une base solide pour la compréhension et la modélisation numérique de ce mécanisme en 1D ou en 2D. // Abstract : This research project was done through an academic partnership between the Université de Sherbrooke and Golder Associés Ltée., a mining consultant from Montréal. The latter had interrogations at regarding consolidation mechanisms controlling thickened tailings deposition, a relatively new approach in tailings management. This type of material are thickened to a point from which they don’t show any segregation, they expulse less water and can be stacked with a greater beach angle than conventional tailings. The combination of this method with the upstream raising method results in the possible reduction of the footprint of the tailings disposal facility. Thickened tailings have not been studied extensively. However, by gathering available information from the existing technical literature, it is apparent that the sole mechanism creating both a dissipation of excess pore water pressure and a settlement following deposition is self-weight consolidation. A settling column monitored with pressure transmitters was used to define accurately the self-weight consolidation process in terms of dissipation of excess pore water pressure. A consolidometer setup was used to define the compressibility of this material during the self-weight consolidation. Experimental results were reproduced with the numerical model CS2 which considers the self-weight consolidation and large strains. Following a few adjustments of the constitutive relationships, the numerical reproduction is clear; it represents closely the experimental results. This made it possible to document certain elements that were not well defined in the technical literature about the self-weight consolidation. The use of the finite element model SIGMA/W and its capability to consider self-weight consolidation within a tailings deposition scheme were evaluated. Firstly, the model capabilities were verified through 1D simulations that helped to document the method to adopt to model the self-weight consolidation. The formulation of SIGMA/W related to the sequential tailings placement was also studied during this phase. A comparison with the model CS4 was also performed. Secondly, the tailings disposal facility was modeled at large scale by including the sequential tailings placement and the consideration of the self-weight consolidation for each deposition. This process allowed evaluating the capabilities of SIGMA/W in large scale analysis. It appears that this numerical tool presents some numerical weaknesses especially with regards to the sequential tailings placement. Moreover, the results of this study place the self-weight consolidation of hard rock thickened mine tailings as an important mechanism that needs to be considered in a deposition scheme as it controls the short term displacements of the impoundment. Finally, they document the self-weight consolidation mechanism and provide reliable information for modelling this process in one or two-dimensional numerical analysis.

Résumé : Ce projet de recherche s’inscrit dans le cadre d’une requête de l’entreprise partenaire, Golder Associés Ltée. Cette dernière s’interrogeait sur la consolidation d’un résidu minier épaissi, une approche de plus en plus utilisée dans le domaine de la gestion des aires de déposition des résidus miniers. Ce type de matériau est épaissi jusqu’à un point où une fois déposé, il ne connaît pas ou peu de ségrégation, rejette moins d’eau et possède généralement un angle de repos plus grand que les résidus conventionnels. L’intérêt de cette approche dans le cadre de cette étude consiste en la réduction des empreintes des aires de déposition par la combinaison des résidus épaissis et des rehaussements par l’amont. La consolidation de ce type de résidus a été peu étudiée depuis leur développement. En rassemblant les observations rapportées dans les écrits scientifiques, il est possible de ressortir que le mécanisme physique générant la dissipation des pressions interstitielles en excès et le tassement au moment de la déposition est essentiellement la consolidation sous le poids propre. Un essai en colonne de tassement instrumentée de transmetteurs de pression a permis l’étude de la consolidation sous le poids propre en termes de dissipation des pressions d’eau avec une grande précision. Un essai en consolidomètre a permis de définir la compressibilité du matériau durant cette étape de consolidation sous le poids propre avec une précision acceptable. Les résultats expérimentaux ont été reproduits à l’aide du modèle CS2 suite à quelques ajustements des relations constitutives. CS2 considère la consolidation sous le poids propre et les grandes déformations d’une déposition instantanée. Le rapprochement entre le modèle CS2 et les résultats expérimentaux est sans équivoque et permet de prendre connaissance de certains aspects de la consolidation sous le poids propre qui étaient peu détaillés jusqu'à maintenant dans les écrits scientifiques. L’importance de la consolidation sous le poids propre et son intégration dans le plan de déposition proposé par l’entreprise partenaire a été évaluée à l’aide du logiciel SIGMA/W. Les capacités de ce logiciel ont tout d’abord été étudiées en 1D. Ces vérifications visaient la considération de la consolidation sous le poids propre tout en examinant la formulation de SIGMA/W pour un remplissage progressif. Ces simulations 1D ont pu être comparées aux résultats du modèle CS4, un modèle calqué sur CS2 qui permet un remplissage progressif. Finalement, une campagne de simulation à grande échelle en 2D visant la simulation d’une aire de déposition de résidus épaissis a permis d’examiner les éléments importants dans la considération de ce mécanisme à l’aide du logiciel commercial SIGMA/W. Il en ressort que le logiciel SIGMA/W n’est pas le logiciel idéal pour simuler la déposition progressive de résidus épaissis en considérant la consolidation sous le poids propre et ce pour maintes raisons. Les résultats de cette étude viennent situer l’importance de la consolidation sous le poids propre dans les résidus épaissis et fournissent une base solide pour la compréhension et la modélisation numérique de ce mécanisme en 1D ou en 2D. // Abstract : This research project was done through an academic partnership between the Université de Sherbrooke and Golder Associés Ltée., a mining consultant from Montréal. The latter had interrogations at regarding consolidation mechanisms controlling thickened tailings deposition, a relatively new approach in tailings management. This type of material are thickened to a point from which they don’t show any segregation, they expulse less water and can be stacked with a greater beach angle than conventional tailings. The combination of this method with the upstream raising method results in the possible reduction of the footprint of the tailings disposal facility. Thickened tailings have not been studied extensively. However, by gathering available information from the existing technical literature, it is apparent that the sole mechanism creating both a dissipation of excess pore water pressure and a settlement following deposition is self-weight consolidation. A settling column monitored with pressure transmitters was used to define accurately the self-weight consolidation process in terms of dissipation of excess pore water pressure. A consolidometer setup was used to define the compressibility of this material during the self-weight consolidation. Experimental results were reproduced with the numerical model CS2 which considers the self-weight consolidation and large strains. Following a few adjustments of the constitutive relationships, the numerical reproduction is clear; it represents closely the experimental results. This made it possible to document certain elements that were not well defined in the technical literature about the self-weight consolidation. The use of the finite element model SIGMA/W and its capability to consider self-weight consolidation within a tailings deposition scheme were evaluated. Firstly, the model capabilities were verified through 1D simulations that helped to document the method to adopt to model the self-weight consolidation. The formulation of SIGMA/W related to the sequential tailings placement was also studied during this phase. A comparison with the model CS4 was also performed. Secondly, the tailings disposal facility was modeled at large scale by including the sequential tailings placement and the consideration of the self-weight consolidation for each deposition. This process allowed evaluating the capabilities of SIGMA/W in large scale analysis. It appears that this numerical tool presents some numerical weaknesses especially with regards to the sequential tailings placement. Moreover, the results of this study place the self-weight consolidation of hard rock thickened mine tailings as an important mechanism that needs to be considered in a deposition scheme as it controls the short term displacements of the impoundment. Finally, they document the self-weight consolidation mechanism and provide reliable information for modelling this process in one or two-dimensional numerical analysis.