BRASILIA, Brazil, Aug. 30 (UPI) — An internal report on Brazil’s Samarco Mineração dam collapse that killed 19 people in November said a design flaw caused the accident.
The technical report commissioned by Samarco’s joint owners, BHP Billiton and Vale, did not assign blame for Nov. 5 disaster at the company’s Fundao reservoir in the state of Minas Gerais.
Dams that hold mining waste, commonly known as tailings, have walls made of a mixture of sand-like particles and clay-like silt. At the Samarco dam, sand in the dam walls became saturated and began to behave like a liquid. A weight increase was placed on the tailings as the height of the dam was raised, which caused the weight of clay-like silt in one part of the dam to push outward — causing the dam to collapse.
“There was a fundamental change in the design concept whereby more widespread saturation was allowed and accepted,” according to the report. “This increase in the extent of saturation introduced the potential for sand liquefaction.”
Samarco last year reached an agreement to pay the Brazilian government a total of about $260 million, although prosecutors said the amount was small. A separate police investigation said the the disaster was caused by misconduct, which Samarco denies.
“The tailings that had been solid ground just minutes before transformed into a roiling river, overtopping but not breaching the downstream Santarem Dam, then entering the town of Bento Rodriguez shortly thereafter en route to its ultimate destination in the sea,” the report said.