Tailings dams are supposed to last forever but they fail regularly due to a series of factors related to the construction and maintenance of the mine site. According to the cronology of mayor tailings dam failures of WISE Uranium Proyect there has been one mayor failure in 2017, two on 2016 and the last one in South America was on 2015 in Minas Gerias - Brasil.
Tailings dams occur over the whole world. From the International Commision of Large Dams review of tailings dam failure occureces [ICOLD 2001] and North America is the place with most mine sites and bigger number of tailings dam failure. Small dams with heights of 15-30 are the ones that fail more [Azam 2010][Rico 2007]. One of the reasons of tailings dam failure is the lack of regulation and poor engineering required at dam construction. Over the last years the concern, regulation and engineering practices have increased and thus result in a decrease on the rate of failures from 50 events/decade from 1960 to 1980s to 20 events/decade over the last 20 years [Azam 2010].
This article show the numerical modeling of a tailings dam failure relate to the Tamboraque site in Peru andes. The model represents the dynamic transport of tailings material as a non-newtonian fluid. Model was developed using high-end open source software as OpenFOAM, Salome Platform and QGIS.
Safety and enviromental risks
Tailings dam failure represent a risk to safety due to the landslide produced that can reach populated areas and highways. On the Tonglvshan Mine in China incident in 2017 two people were reported dead, at the Germano Mine in Brasil 17 peopled died from the landslide. Besides the fatality, houses are destroyed and people are force to leave the place.
Many enviormental concerns are related to the tailings dam failures since the material spilled is rich on metals, sulfates and might have arsenic, nitrates or cyanides. The presence of mine tailings over the land surface will interact with the surface water and underground water upon the climatic / hydrologic conditions of the area. Its is a important to remenber that most of the tailings dam failures are related to weather conditions [Azam 2010], so the failure escenario might be related to high flow on the streams that will spread contaminants kilometers downstream and infiltrate them on the aquifers.
A research on the available software specifically for the landslide modeling of mine tailings was done. Not many were found and most of them were related to slope stability but no for landslide simulation. Some cases of landslide modeling were found done with commercial software as Ansys and open source software as Open Foam.
OpenFOAM was selected for this numerical simulation. The failure escenario is conceptualized as the licuefaction of the tailings material due to external forces as physical stress or seismicity. Licuefaction is the phenomenon where soils loses strengh and behave as a liquid. Tailings dam as a liquid are supposed to work as a non-newtonian fluid where viscosity is not constant. The Herschel-Bulkley rheological model was selected to describe the relation in between the viscosity and the velocity.
About the model
The geometry of the tailings dam was processed on QGIS and then translated to a local coordinate systen on Salome Platform. Numerical work was done on Windows operating system with OpenFOAM for Windows.
The model has 330780 nodes, 134360 triangles and 1753872 tetrahedrons. The landslide of tailings lasted 22 seconds and results are showed every 0.2 seconds. Simulation itself is very heavy and computer intensive, on a Core i7 the simulation lasted 20 hours.
These are some videos from the tailings landslide simulation
Shahid Azam, 2010, Tailings Dam Failures: A Review of the Last One Hundred Years, URL: http://www.infomine.com/library/publications/docs/Azam2010.pdf
ICOLD (2001). Tailings Dams - Risk of Dangerous Occurrences, Lessons Learnt from Practical Experiences, Bulletin 121.
M. Rico, G. Benito, A.R. Salgueiro, A. Dıez-Herrero, H.G. Pereira, 2007, Reported tailings dam failures A review of the European incidents in the worldwide context. URL: https://www.researchgate.net/profile/Mayte_Rico/publication/5985618_Reported_tailings_dam_failures_A_review_of_the_European_incidents_in_the_worldwide_context/links/00b49517f8b2ba20a6000000.pdf