Construction details in the tailings dam at Vale’s (NYSE: VALE) Corrego do Feijao iron ore mine in Brazil may have caused the burst that killed at least 270 people when 10 million cubic metres of sludge destroyed neighbouring settlements and took out a railway bridge, according to Swiss researchers.
Why the dam broke in 2019 specifically – three years after the pond was last loaded with new tailings – and why no significant displacements had been detected before the collapse, is the focus of a new paper by scientists at the university ETH Zurich.
The researchers recount how that the tailings pond was built in 1976 in Brumadinho in the country’s southeast. Over the following years, its earth dam was raised several times by a few metres, as is customary in ore mining, to create additional space for the storage of residues. The dam’s steps were placed with an offset on top of each other, much like the steps of a staircase.
Ultimately, the dam consisted of 10 steps and was 86 metres tall. When the structure failed, the initial rupture occurred at the second dam level. As a result, all 10 steps of the earth dam collapsed and, together with the liquefied accumulated tailings, ran out down into the valley as a mudslide.