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Samarco dam disaster probe reveals construction and design flaws

Tuesday, 30 Aug 2016 07:22:21 | Peter Ryan

Men take out a bag from a house flooded with mud after a dam owned by Vale SA and BHP Billiton burst in Brazil. (Reuters: Ricardo Moraes)

A 10-month investigation into last year's Samarco mine disaster in Brazil has found the fatal collapse in November 2015 was due to a range of construction and design flaws.

The resulting catastrophic collapse of a tailings dam killed 19 people, damaging the reputations of BHP Billiton and its partner Vale which remain locked in a compensation battle with the Brazilian Government.

The report points to "unplanned occurrences" in the dam's construction that established the conditions for the failure to take place.

The investigation found that a change in the dam's design in 2011 and 2012 resulted in less efficient drainage.

That caused a process called "liquefaction" in the dam wall, causing soil in the wall to weaken and become structurally deficient.

Vale, Samarco and BHP jointly commissioned international law firm Cleary Gottlieb Steen and Hamilton to investigate the immediate cause of the failure.

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The firm was joined by geotechnical specialists, led by Dr Norbert Morgenstern, a university professor in civil engineering.

"In November 2015, BHP Billiton committed to making the findings of this investigation public, and we are determined to learn from this tragedy," BHP chief commercial officer Dean Dalla Valle said in a statement.

"This important technical study will improve our understanding of what happened at Samarco.

"We have shared these findings so that the sector can learn from the dam failure and develop and implement further standards that can help prevent a similar event like this happening again."

The investigation also noted a related aspect of the failure was a series of three small seismic shocks that occurred 90 minutes earlier, that is "likely to have accelerated the failure process that was already well advanced," the report said.

Brazil's federal police had in June formally accused Samarco, the joint venture between Vale SA and BHP Billiton, of wilful misconduct.

"Samarco has long claimed it performs good practise but the report did not demonstrate this," Carlos Eduardo Pinto, a prosecutor in the case against Samarco, told Reuters.

"Quite the opposite, it showed the company altered the project in a way that would not have been permitted."

In July, BHP doubled its provisions for the disaster to well in excess of $3 billion.

The company also said it was encouraged by the progress efforts to remediate damage, but still intended to appeal an $8 billion public civil claim.

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