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WORLDWATCH DAMS

Many commentators argue that, as the cheapest and least stable form of tailings dam, upstream technology is inherently problematic and should be scrapped altogether. Some engineers favour the downstream dam, in which successive loads of tailings are deposited downstream of the initial wall rather than upstream. Dr Barry Wills, senior partner of the journal Minerals Engineering International writes that: ‘Downstream dam building is the only method that permits design and construction of tailings dams to acceptable engineering standards.’

However, Durve disagrees and says that both types of structure can be stable or unstable depending on how they are constructed. ‘Instability will arise in either case if sufficient consideration is not paid to seepage and the position of the phreatic surface,’ he says. What’s essential, as he noted in 1985, is constant monitoring of the water pressure in the wall – something he claims is cheap and easy to do using water pressure monitors.

In the aftermath of the disaster, Vale stated that there was no evidence of an imminent risk of collapse at Brumadinho and that it consistently monitored water pressure. But a string of media reports (along with the arrest of eight Vale employees) indicated that the company and one of its contractors knew of significant issues. On 11

February, Reuters stated that it had seen an internal Vale report dated October 2018 which classified the dam at Brumadinho as being two times more likely to fail than the maximum level of risk tolerated under internal guidelines. According to the Guardian, a September 2018 report by the German certifications contractor TÜV SÜD concluded that the Brumadinho dam was stable but highlighted drainage problems and recommended installing new water pressure monitors. Vale stated that ‘workers were fitting the new monitors on the day the dam burst’.

Further reporting by the Wall Street Journal in February, based on police reports, court documents and arrest

More tailings dam failures are predicted which will could to more loss of life and property

8 • Geographical

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