This thesis examines the 2018 failure of the Northern Tailings Storage Facility at Cadia Valley Operations, located in New South Wales, Australia. First, the importance of examining and understanding failure mechanisms and post failure kinematics is described. Within which we understand that in the current state of affairs it is exceedingly difficult, or nigh impossible to perform without the use of large strain analyses, which have yet to permeate into the industry to a significant degree. Second, the initial construction and state of the dam just prior to failure is defined, with the materials and their properties laid out and discussed in depth as well as our means of modeling their behavior. Third, we validate and discuss our results of the base model of the dam based on key topographic features from initial and post-failure field measurements. After validation, we examine the influences of each of the different materials on the runout, comparing final topographies of different simulations with the actual final topography observed. This study was a valuable method of validating the Material Point Method as a means of modeling large deformations, as well as demonstrating its powerful applications towards catastrophic disaster prevention. The study validates and provides a greater understanding of the event of the Cadia Tailings Storage Facility Failure, and presents a framework of steps to perform similar examination on future tailings dams as a means of providing risk management in the event of failure. / Master of Science / Tailings dams are structures integral to the life cycle of mining and mineral processing. After mining and the processing of mined materials, the leftover material, known as "tailings" are pumped and stored behind these structures, usually indefinitely. These structures are unique because they are usually expanded as additional storage space for these materials is required. Over the past several decades, the rate at which catastrophic or serious tailings dam failures occur out of failures has been on the rise. Because of this, it becomes necessary to better understand the failure and post-failure movements of the dam. This thesis presents one such failure, the Cadia Tailings Dam Failure of 2018, which is located in New South Wales, Australia. It applies the Material Point Method, a numerical method which allows for largestrain deformations, to examine the post-failure mechanism and interpret various influences by the different materials on the final runout. Because of this, the paper provides insights on the importance of understanding large strain analyses, discussing and presenting the incidents of the failure. The model used for reference is validated using topographic and field data taken after the failure, allowing for a comparison with future models which vary the geometry and material characteristics of the event. A procedural plan is proposed to apply to future analyses, allowing for the analysis to be applied to other events and tailings dam structures, for further insight on influences of variability and material properties on post-failure topography and geometry.

No description available.

No description available.

Tailings storage facilities (TSFs) serve as structures for storing tailings, i.e., waste materials generated by the mining industry. In recent years, tailings dam failures and collapse of these constructions have been reduced due to the establishment of regulations to control these structures, nevertheless, the consequences are catastrophic when tailings dam failures occur. There are some different construction methods for tailings dams. One common construction method is the upstream method; where the dam is raised by constructing embankments on top of the tailings stored in the impoundment. Thus, it is essential to understand the mechanical and geochemical behavior of deposited tailings to be able to perform safety assessments of tailings dams.  Material properties must be assessed for the present time as well as over a longer time since aging and continuous deposition might change the mechanical behavior over time. Continuous deposition leads to continuous increased vertical stress on particles, and there is a need to study if increased vertical stress can lead to a possible change of the mechanical properties of tailings. Therefore, this study has investigated the characteristics of tailings particles after being subjected to vertical stepwise loading. This study focuses on investigating the impact of particle breakage (or crushing) on tailings by analyzing material recovered from a tailings dam in Sweden. The research was performed on disturbed tailings material from a borehole of approximately 40 m depth. The study was conducted on four samples recovered 10 m apart, developing a characterization of the material and laboratory tests on each of them. The characterization consisted of the determination of intrinsic properties such as particle size distribution, particle shape, and mineralogy before and after testing; while the laboratory tests were conducted by means of the odometer test. The laboratory tests employed the oedometer test, which applies a vertical load in slow increments under K0 conditions to simulate the behavior of tailings consolidated in the impoundment. The results obtained from the oedometer tests showed interesting observations regarding changes in particle size distribution (PSD) before and after testing. Based on this study it is hard to conclude if the change in PSD solely is caused by crushing. Three samples show a PSD after oedometer which have slightly more fines than before oedometer, while the last sample has neglectable change in PSD. Theoretically, this small change in PSD indicates that larger tailings particles exhibited a higher susceptibility to some degree of crushing, but since the change is so small it cannot be excluded that the changes origins from the accuracy of determining the PSD.  The samples taken at different depths were prepared using the tamping method, and the oedometer testing indicated minimal differences in their compression characteristics, and since the soil fabric was destroyed under sampling and then reconstituted through tamping this is expected. To investigate the influence of particle arrangement on the compression and potential crushing, one of the samples was tested in a slurry configuration. This test demonstrated that particle arrangement appears to be a contributing factor to crushing, as it showed less deviation in particle size distribution compared to the tamped sample. To contextualize and validate the findings, the results were correlated, evaluated, and compared with previous studies conducted on tailings from the same tailings storage facility (TSF). Although future research on crushing in correlation of mineralogy respectively and changes in particle shape are needed, this comparative analysis has provided input that can contribute to enhanced understanding of tailings behavior under increased vertical load.

Gold mining in the Witwatersrand Basin of South Africa has resulted in soil contamination due to the lack of sufficient environmental management plans for the tailings dumps and remnant footprints. Tailings reclamation as a strategy of reducing pollution in the Central Rand, for instance, has resulted in contamination of water systems by acid mine drainage (AMD). After removal of the tailings dumps, remnant material is left over on the tailings footprints and these contain significant amounts of pollutants that were initially in the tailings. Heavy rainfall during summer dissolves primary minerals and later in the dry season, secondary minerals are precipitated as efflorescent crusts on and nearby tailings dumps as well as footprints due to high evaporation. The efflorescent crusts can redissolve when it rains and form acidic, metal and sulphate-rich solutions due to their soluble characteristics. This study aimed to characterise tailings footprints in areas targeted for human settlements and office spaces to assess their potential to release left over toxic elements such arsenic (As), lead (Pb), copper (Cu) and zinc (Zn). The approach to the study involved characterisation of oxidised and unoxidised tailings material and secondary precipitates on both tailings dumps and footprints. This involved determining the mineralogical composition using Powder X-ray Diffraction (PXRD). Dissolution and leaching studies were also conducted on the material followed by determination of constituent elements using inductively coupled plasma optical emission spectroscopy (ICP-OES) and sulphates using ion chromatography (IC). The leaching solutions used included rainwater; dilute sulphuric acid at pH of 3.0 (a common leachate in such acidic soils); as well as plant exudates such as oxalic and citric acids. The leachate solutions were used to correlate the mineralogical composition of secondary precipitates and tailings footprints. Potential implications on humans following any accidental ingestion of the tailings or contaminated soils were assessed using gastric juices. The ecological risk factors and risk index together with the model to evaluate daily intake and different pathways to humans were used to assess the toxicity caused by exposure to contaminants in the materials. The experimental work was augmented by computer simulations based on geochemical modelling (using the PHREEQC geochemical modelling code) to determine the speciation of elements (and thus their potential lability and bioavailability), dissolution and formation of secondary mineral precipitates in the tailings dumps and footprints. The findings of the PXRD study showed that the mineralogy of the tailings and footprints was dominated by quartz (SiO2) and some minor minerals such as pyrite (FeS2), pyrophyllite (Al2Si4O10(OH)2), chlorite (Mg,Fe)3(Si,Al)4O10), mica (K(Mg,Fe)3 AlSi3O10(F,OH)2) while that of secondary precipitates was dominated by jarosite (KFe3+ 3(OH)6 (SO4)2), goethite (FeOOH), melanterite (FeSO4.7H2O) and gypsum (CaSO4.2H2O). Minerals obtained for the secondary precipitates were corroborated by geochemical modelling. Leaching results using rainwater with pH ranges from 3.5 to 3.9 showed that trace elements are released very slowly from tailings dumps and footprints and in small concentrations during rainy seasons as follows: As (1.5 mg/L-4.5 mg/L), Pb (3.5 mg/L-5.5 mg/L), Cu (4 mg/L-4.8 mg/L) and Zn (23 mg/L-44 mg/L). The release and mobility of Cu, Pb, Zn and As occurs quite markedly when secondary precipitates dissolve, making the immediate impacted environment unfavourable for plant growth and any habits in the vicinity. This was substantiated by simulated dissolutions and assessment of the resulting elemental speciation that pointed to the elements being distributed in bioavailable forms, implying potential uptake by plants (such as vegetables that may be cultivated on such impacted soils). The model was used to evaluate the daily intake and different exposure pathways and the results showed that children may daily intake 48.4 mg kg-1 day-1 and adults‟ 32.8 mg kg-1 day-1 . After 5 years (1825 days) of exposure more harm may be experienced and findings shows that kids are the most victims on these contaminated sites compared to adults. Both children and adults may absorb low levels of these toxic elements daily and after long time of exposure it may cause disease like cancer in their body which may lead to death. Pathways may be through inhalation and accidentally ingesting tailings soil that contain toxic elements. Drawing from the above findings, it will be important that tailings footprints that have been earmarked as land for development (residential or office space) be thoroughly assessed for potential release of toxic elements and high levels of acidity. Further reclamation aimed at reducing these hazards can then be implemented. / College of Agriculture and Environmental Sciences / M. Sc. (Environmental Science)

MESMEG / Department of Mining and Environmental Geology / See the attached abstract below

Vegetation establishment is one of the major rehabilitation methods that are used to stabilize, cover, to minimize, mitigate or remove the contaminants from tailings storage facilities (TSF’s). Phytostabilization is a useful mechanism by which plants limit the contamination of natural systems with toxic elements. For successful occurrence of phytostabilization on mine tailings, it is vital to establish plant species that can survive the hostile conditions of the substrate. Major problems encountered with vegetation covers is the lack of natural soil properties e.g. soil structure, organic carbon and also hostile chemical conditions. Only a few species are tolerant to the different negative properties of the tailings. The main aim of this project is to identify plant species that can be used for vegetative rehabilitation of nine different types of tailings material including gypsum, gold, platinum, kimberlite, coal, fluorspar and andalusite tailings. The ability of 28 different plant species to survive in the tailings was assessed by statistically calculating the growth potential of the species and summarizing the data in graphs and an index table that calculates a specific merit value for each of the tailings-species combinations. The various plant stress factors that the species exhibited were also documented. Finally, the results were correlated with a soil physical and -chemical baseline study of the tailings to provide insight into successes and failures of certain species. The final results identified various successful tailings-species combinations, as well as failures. The index table proved to be a useful tool to identify suitable species for establishment on various tailings. The baseline study of the different tailings could be used to explain why certain species could be established successfully, as well as the reason why some species did not survive. / M (Environmental Sciences), North-West University, Potchefstroom Campus, 2015

Vegetation establishment is one of the major rehabilitation methods that are used to stabilize, cover, to minimize, mitigate or remove the contaminants from tailings storage facilities (TSF’s). Phytostabilization is a useful mechanism by which plants limit the contamination of natural systems with toxic elements. For successful occurrence of phytostabilization on mine tailings, it is vital to establish plant species that can survive the hostile conditions of the substrate. Major problems encountered with vegetation covers is the lack of natural soil properties e.g. soil structure, organic carbon and also hostile chemical conditions. Only a few species are tolerant to the different negative properties of the tailings. The main aim of this project is to identify plant species that can be used for vegetative rehabilitation of nine different types of tailings material including gypsum, gold, platinum, kimberlite, coal, fluorspar and andalusite tailings. The ability of 28 different plant species to survive in the tailings was assessed by statistically calculating the growth potential of the species and summarizing the data in graphs and an index table that calculates a specific merit value for each of the tailings-species combinations. The various plant stress factors that the species exhibited were also documented. Finally, the results were correlated with a soil physical and -chemical baseline study of the tailings to provide insight into successes and failures of certain species. The final results identified various successful tailings-species combinations, as well as failures. The index table proved to be a useful tool to identify suitable species for establishment on various tailings. The baseline study of the different tailings could be used to explain why certain species could be established successfully, as well as the reason why some species did not survive. / M (Environmental Sciences), North-West University, Potchefstroom Campus, 2015

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.