Fernando Alcoforado*
The rupture of ore tailings dam caused social and environmental disaster in Brumadinho, Minas Gerais, with the leakage of 13 million cubic meters of ore tailings repeating the same event that occurred in Mariana, district of Bento Rodrigues, in 2015. This quantity is a quarter of what leaked from the Fundão dam in Mariana three years ago. The dam that broke in Brumadinho is called dam of upstream elevation, the same type of dam in Fundão that annihilated the district of Bento Rodrigues in Mariana in 2015. To understand the rupture of the tailings dams in Brumadinho and its consequences, it is necessary to understand concepts and definitions related to the types of ore tailings dams to adopt those that avoid the repetition of similar disasters to those occurred in Bento Rodrigues and Brumadinho in Minas Gerais. The video below shows how the Brumadinho dam disruption occurred: <https://www.topbuzz.com/a/6650799509586575878?c=msgr&user_id=6289028454420612100&language=pt®ion=br&app_id=1116&impr_id=6650830037631109381&gid=6650799509586575878>.
What is a ore tailings dam? It is a land structure built to store mining waste, which is defined as the sterile fraction produced by the beneficiation of ores, in a mechanical and / or chemical process that divides the raw ore into concentrate and tailings. A tailings dam is built by raising tailings. There are three methods of elevationing:
- Upstream elevation
- Downstream elevation
- Center line elevation
References: RAFAEL, Herbert Miguel Angel Maturano. Análise do potencial de liquefação de uma barragem de rejeito. Pontifícia Universidade Católica do Rio de Janeiro. Departamento de Engenharia Civil, 2012 and FREIRE NETO, João Pimenta. Estudo da liquefação estática em rejeitos e aplicação de metodologia de análise de estabilidade. Núcleo de Geotecnia da Escola de Minas da Universidade Federal de Ouro Preto, 2009.
The upstream elevation method consists initially in the construction of an initial or starting dam, usually using compacted landfill or rockfill. The tailings are discharged hydraulically, by cannons or hydrocyclones, from the crest (topmost) of the starting dam, forming a tailings beach which will eventually be densified and will serve as a foundation and will provide material for future dykes of elevation, which will be constructed with the waste material itself. The process is repeated until the magnification quota foreseen in the project is reached. This method is the simplest and has the lowest construction cost, but it is associated with the majority of the cases of rupture of tailings dams around the world, as in the case of Samarco in Bento Rodrigues and now in Brumadinho. The video presented below shows how the dams based on the upstream elevation method that broke in Bento Rodrigues and Brumadinho were constructed: <https://globoplay.globo.com/v/4596137/>.
The downstream elevation method is more conservative in the sense that it was developed to reduce the risks of liquefaction in areas of seismic activity. The installation of an impermeable core and drainage zones allow this type of bus to contain a substantial volume of water directly in contact with its upstream talus, without compromising the stability of the structure. In the same way as in the upstream elevation method, a starting dam with compacted landfill or rockfill is initially constructed. The tailings are deposited upstream of this dam. À medida que a borda livre é atingida, são feitos alteamentos sucessivos para jusante. As the free edge is reached, successive elevations are made downstream. The main advantage of this method is the lack of stability constraint for the final height of the bus, since each elevation is structurally independent of the upstream tailings. The disadvantages are the high cost of the dam, due to the large volume of landfill needed, besides the large area occupied by the dam. Thus, the limitation of the final height of an upstream tailings dam will depend primarily on the available area of land.
The method of center line elevation has stability superior to that of the barrage of upstream elevation, however does not require a volume of materials as great, as in the upstream elevation. In the same way as in the other two methods, a starting dam is constructed in order to form an upstream tailings beach. The tailings disposal system is similar to the upstream retention method: tailings are launched from the crest of the initial dike. When discharges become necessary, new dykes are constructed, both on the tailings disposed upstream and on the embankment of the previous dam, so that the axis of symmetry is maintained.
Therefore, from the dams of tailings to which it implies greater risks is the upstream elevation method such as those that broke in Bento Rodrigues and Brumadinho and those of lesser risk is of center line elevation method that should be the solution to be demanded by environmental legislation aimed at preventing the recurrence of disasters.
Most likely, the disasters in Bento Rodrigues and Brumadinho occurred either because of the irresponsibility in choosing the type of tailings dam to be implanted, due to negligence in the maintenance of the dams, or in the lack of supervision by the competent public agencies, in addition to the lack of plans to deal with catastrophic situations like the one that happened in Mariana. If dams were implemented based on the method of elevation in the center line instead of upstream elevation method these disasters could have been avoided. The Samarco and Vale dams in Brumadinho must have broken due to Vale’s negligence and failures in inspection by the competent agencies. Many deaths could have been avoided if a contingency plan with notices or sound of any nature existed so that people in the area were not surprised by the catastrophic event. The impunity of those responsible for the disaster in Bento Rodrigues also contributed to Vale’s recidivism in 2019 of the same crime committed in 2015.
It can be categorically stated that the social and environmental disasters that occurred with the dam rupture in Bento Rodrigues and Brumadinho could have been avoided if Samarco and Vale, respectively, responsible for the construction and maintenance of the dams operated correctly and safely. Therefore, managers and executives of Vale do Rio Doce, BHP Billiton and Samarco should be held accountable for the unrelenting social and environmental crime that occurred with the rupture of the dams in the district of Bento Rodrigues in Mariana and Brumadinho. It is necessary that these companies and their leaders pay compensation for the social and environmental damage caused and be criminally liable to serve as an example so that events of this nature do not happen again.
* Fernando Alcoforado, 79, holder of the CONFEA / CREA System Medal of Merit, member of the Bahia Academy of Education, engineer and doctor in Territorial Planning and Regional Development by the University of Barcelona, university professor and consultant in the areas of strategic planning, business planning, regional planning and planning of energy systems, is the author of 14 books addressing issues such as Globalization and Development, Brazilian Economy, Global Warming and Climate Change, The Factors that Condition Economic and Social Development, Energy in the world and The Great Scientific, Economic, and Social Revolutions that Changed the World.
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