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The dry closure of the Almagrera tailings dam: detailed modelling, monitoring results and environmental aspects

  • José L. Justo
  • Antonio Morales-Esteban
  • Enrique Justo
  • Francisco A. Jiménez-Cantizano
  • Percy Durand
  • Manuel Vázquez-Boza
Case history

Abstract

The Aznalcóllar tailings dam failure moved the Spanish authorities to pay attention to tailings deposits. The Almagrera tailings dam holds one of the largest mining waste deposits in Andalucía. The dry closure of this dam has been detailed in this manuscript. Some serious difficulties had to be solved. Firstly, the dam had undergone up to five raisings before the closure operations started, and this process had not been properly documented. Secondly, the reservoir water was contaminated by the toxic tailings placed several metres below and, due to the high acidity of this water, the geotechnical characterization of the tailings deposit has been really challenging. Thirdly, the definition of the model itself has been a complex task due to the consideration of many phases and different hypotheses. In the finite element calculation, a constitutive model of perfect non-associated plasticity has been used for the dam and a soft soil creep model for the tailings. Next, it has been decided to decontaminate a closed mine by placing its abandoned material—Las Viñas fill—on top of the tailings deposit inside the reservoir. This operation generated important settlements on the tailings deposit. These settlements had to be accelerated by placing drainage wells to avoid the cracking of the final cap. The safety factor during the dry closure operations under dynamic loading was insufficient and a compacted rockfill reinforcement had to be laid on the downstream slope of the dam. Very few papers describe a successful dry closure of a tailings dam as is done here.

Keywords

Dry closure Tailings dam Toxic deposit Settlement Safety factor Drainage wells 

Resume

La rupture du barrage de stériles d’Aznalcóllar a poussé les autorités espagnoles à prêter attention aux dépôts de résidus. Le barrage de stériles d’Almagrera abrite l’un des plus importants dépôts de déchets miniers d’Andalousie. La fermeture à sec de ce barrage est présentée dans ce manuscrit. Certaines difficultés sérieuses ont dû être résolues. Premièrement, le barrage avait connu jusqu’à cinq surélévations avant le début des opérations de fermeture et ce processus n’avait pas été correctement documenté. Deuxièmement, l’eau du réservoir a été contaminée par les résidus toxiques placés plusieurs mètres plus bas et, en raison de la forte acidité de cette eau, la caractérisation géotechnique du gisement de résidus a été très difficile. Troisièmement, la définition du modèle lui-même a été une tâche complexe en raison de la prise en compte de nombreuses phases et d’hypothèses différentes. Dans le calcul par des éléments finis (EF), un modèle constitutif de plasticité parfaite non associée a été introduit pour le barrage et un modèle visqueux pour les déchets miniers. Ensuite, il a été décidé de décontaminer une mine à proximité—Las Viñas—en plaçant son matériau abandonné au-dessus du dépôt de résidus à l’intérieur du réservoir. Cette opération a généré d’importants tassements sur le dépôt de résidus. Ces tassements ont dû être accélérés en plaçant des puits de drainage pour éviter la fissuration de la couverture finale. Le coefficient de sécurité (CS) à la fin des opérations de fermeture à sec sous chargement dynamique était insuffisant et des renforts d’enrochement compactés devaient être posés sur la pente aval. Pas beaucoup d’articles décrivent une fermeture à sec réussie d’un barrage de stériles comme cela est. fait ici.

Mots clés

Fermeture à sec Barrage de stériles Dépôt toxique Tassement Coefficient de sécurité Puits de drainage 

Notes

Acknowledgements

The help provided by the Spanish Ministry of Science and Innovation through the project BIA2010-20377 and by the Instituto Universitario de la Construcción y Arquitectura for revising the English are acknowledged.

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Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2018

Authors and Affiliations

  1. 1.Department of Building Structures and Ground EngineeringUniversity of SevilleSevilleSpain
  2. 2.Environment and Water Agency of Andalusia (Spain)AndalusiaSpain

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