BHP Billiton has said it was not made aware that cracks had been observed on the wall of a tailings dam in the years leading up to its collapse in November 2015, despite co-owning the operation with Brazilian miner Vale.
The Fundão tailings dam at the Samarco mine in south-eastern Brazil collapsed last November, flooding towns below and killing at least 19 people.
Samarco was a self-contained mining operation co-owned by BHP and its Brazilian rival Vale.
A new report, commissioned by BHP and Vale and released on Tuesday, found design flaws, construction defects and other factors resulted in the liquefaction of sand in the dam wall.
“There was a fundamental change in the design concept whereby more widespread saturation was allowed and accepted,” the report said. “This increase in the extent of saturation introduced the potential for sand liquefaction.”
BHP chief executive Dean Dalla Valle said the miner was “determined to learn from this tragedy”.
“This important technical study will improve our understanding of what happened at Samarco,” he said.
“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 full report is available at fundaoinvestigation.com
Separate to the commissioned investigation into the Samarco disaster, BHP has also conducted reviews of its other significant dams, at both its own operations and its non-operated minerals joint ventures.
“In the wake of this event, we have separately undertaken a comprehensive review of our significant dams, which has confirmed that those dams are stable,” Dalla Valle said.
“We will take a number of actions to further enhance risk management at these facilities.
“We have looked comprehensively at tailings dam management and benchmarked to global leading practice.
“We have assessed our portfolio of dams against these global standards and are implementing actions to enhance the management of our dams.”