Seismic performance of tailings dams

Started: March 2018

Supervisors: Dr. Stavroula Kontoe, Prof. Lidija Zdravkovic

Fundings: The National Commission for Scientific and Technological Research (CONICYT – Chile); Dixon Scholarship (Department of Civil & Environmental Engineering, Imperial College London).

Background

The mining production worldwide results in vast amounts of residues leading to the construction of new tailings dams. As site availability is limited due to environmental restrictions, tailings dams tend to be very large, with heights over 200m, often raising stability concerns.
Past experience has shown that failures of tailings dams during earthquakes can be catastrophic, with detrimental consequences for the local communities, environment and the economy. Prominent examples of such cases are the failure of the El Cobre Dam in Chile due to the 1965 earthquake and more recently the failure of Fundão tailings dam in Brazil in November 2015. Therefore, it is important to ensure both the static and seismic stability for this dam type.
There are several aspects and challenges relating to the stability analysis of tailings dams which are not common in comparison with traditional earth dams: a) the construction methods are closely dependent on the availability of coarse fraction of the tailings material (usually sand); b) tailings dams normally include a basal drainage system that maintains the control of the water level inside the dam; c) they are usually constructed with highly compacted sand and d) tailings slimes are deposited with high water content.

Project description and research aims

This research project investigates both the static and dynamic response of tailings dams through advanced finite element (FE) analyses, in which the behaviour of tailings sands and slimes is modelled rigorously in accordance with the critical state framework. Selected case studies are considered, for which both geotechnical and seismic data are available. The analyses are performed with the Imperial College Finite Element Program (ICFEP; Potts & Zdravkovic, 1999), following closely the construction sequence in order to reproduce realistically the static in-situ stresses of different tailings construction configurations. The seismic response is evaluated in time domain considering all aspects of the response of tailings sands and slimes under dynamic loading, including liquefaction, during strong ground motions.

The research aims to improve the understanding of the mechanisms leading to instability of tailings dams and hence contribute to advancements in their design, in terms of the adopted configuration and construction methods. The possibility of adopting less conservative slope profiles and the construction through centre-line configurations, under both static and seismic conditions, is one of the issues to be examined. The ultimate aim is to provide guidelines for the development of cost-effective alternative design solutions for the mining industry.
Bibliography

Blight, G. E. (2010). Geotechnical engineering for mine waste storage facilities; London, CRC Press.

Ishihara, K. (1993). Liquefaction and flow failure during earthquakes. Géotechnique 43(3), 351-451

Jamiolkowski, M. (2014). "Soil mechanics and the observational method: challenges at the Zelazny Most copper tailings disposal facility." Géotechnique 64(8): 590-618.

Jefferies, M. and K. Been (2015). Soil liquefaction: A critical state approach. Applied geotechnics series. CRC Press

Potts, D. M. and L. Zdravkovic (1999). Finite element analysis in geotechnical engineering: Theory. London, Telford.

Valenzuela, L. (2015). Tailings dams and hydraulic fills. Casagrande Lecture, XV Panamerican Conference on Soil Mechanics and Geotechnical Engineering, Buenos Aires

Verdugo, R. (2011). Seismic stability analysis of large tailings dams. Proceedings 5th International Conference on Earthquake Geotechnical Engineering, Santiago, 359-383

Vick, S. G. (1990). Planning, design, and analysis of tailings dams. Vancouver, BiTech.