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Liquefaction blamed for Brazil dam collapse

 

State officials in Brazil have suggested that liquefaction was the rigger of the fatal tailings dam collapse on 25 January Vale Mining’s Córrego do Feijão iron ore site in Brumadinho, which is now confirmed to have killed 110 with 238 people still missing.

Vale has said that instrumentation installed at the site did not detect any issues before the collapse and local reports suggest that warning alarms were not triggered, giving those downstream little chance of escape.

Footage of the collapse has now emerged on You Tube and landslide specialist Dave Petley, who is also who is Sheffield University pro vice chancellor (research and innovation), has reviewed the footage and has described the footage (below) as deeply alarming and called for proper tailings management and worldwide change to prevent further collapses at other mine sites.

Last week a number of officials and two engineers were arrested in the wake of the collapse.

Vale has now announced that it has worked with independent consultant Korn Ferry to appoint a committee to undertake an investigation and a chair of another committee to oversee support and recovery. The investigation committee will be led by former minister of the Federal Supreme Court and of the Electoral Superior Court Ellen Gracie. Gracie will be supported by a number of external appointments including Mecasolo Engenharia e Consultoria geotechnical engineer Jean-Pierre Paul Rémy, EY leadership partner of the forensic department Jose Francisco Compagno. The support and recovery committee will be led by Comissão de Valores Mobiliários president Leonardo Pereira.

Failure analysis

Landslide specialist Dave Petley described the failure in his blog: “At the crest of the dam active deformation can be seen – the dark line is a scarp forming as the mass moves downwards. The toe is probably bulging, but this is not really clear.

“The slope then starts to go through a massive rotational failure that extends across the full width and involves the full height of the dam.

“The front of the mass is starting to break up and the failure transitions to a high velocity flow.

“Further rotational slips occur on the back scarp, but the front of the flow is travelling very rapidly. To me this look to have the characteristics of a debris avalanche rather than a debris flow – the presence of so much dust suggests that this frontal portion might not be saturated. But I would be interested in other views.

“The remarkable thing here is that the mass failed as a single landslide involving the full width and full height. There is now sense of a small slip destabilising the mass, or of a series of events, or of retrogression. I find this surprising.”

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