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This determines how dangerous a dam failure can be

When a mining dam burst in Brazil in 2019, nearly ten million cubic metres of toxic sludge surged down the valley, claiming over 270 lives. A Norwegian study shows what may be crucial for understanding the consequences of such a failure.

The landscape turned into mud after the Brumadinho disaster in Brazil in 2019. The dam failure is one of the most severe in modern times.
Per Olav Solberg COMMUNICATIONS ADVISER
Presented by: Presented by: Presented by: Norwegian Geotechnical Institute
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To extract metals such as iron, copper, or gold, rock is crushed into powder and mixed with large amounts of water and chemicals.

The result is a wet, muddy mass – mine waste – which must be stored safely. A tailings dam is an artificial reservoir that retains waste from mining operations.

Mining companies therefore build dams to contain this waste. Behind such dams, enormous amounts of sludge and water can accumulate, effectively forming artificial lakes.

Luca Piciullo is the lead author of an award-winning article that offers insight into how the consequences of dam failures can be assessed.

Dam height matters

If a dam fails, the consequences can be catastrophic. 

A well-known example is the Brumadinho disaster in Brazil in 2019, where almost ten million cubic metres of sludge poured out. The flood wave killed more than 270 people and devastated the valley’s environment for decades to come.

Researchers at the Norwegian Geotechnical Institute (NGI) have analysed an updated global database of dam failures.

The goal was to determine which factors best explain how much material is released when a dam collapses.

“Previously, the total storage volume was often used to indicate how much could be released. We’ve shown that by including the dam's height, you get a more accurate estimate of the released volume,” says researcher Luca Piciullo, who led the study. He works as a senior specialist in dam safety at NGI. 

The upstream method stands out

The analysis also shows that the construction method plays a significant role in safety. The so-called upstream method – where new dam layers are built on top of wet tailings – is clearly overrepresented in the accident statistics.

“The method is inexpensive and widely used, but produces a less stable structure. Our data confirm that upstream dams are especially vulnerable to liquefaction, a phenomenon in which solid materials suddenly lose their strength and begin to behave like a liquid. In Norway, we see a similar effect in quick clay slides,” explains Piciullo.

The researchers also investigated whether the size of the water surface – the area of water that collects on top of the dam – affects how much sludge is released in a dam failure. 

Contrary to earlier assumptions, they found no such correlation.

A more reliable method

“Our research aims to provide both the industry and research community with a more reliable, data-driven method for estimating how much material will actually be released if a tailings dam fails,” says Piciullo.

The article was selected as one of Engineering Geology's six best publications from the past three years, based on peer review and citations.

Reference:

Piciullo et al. A new look at the statistics of tailings dam failures, Engineering Geology, vol. 303, 2022. DOI: 10.1016/j.enggeo.2022.106657

Mine waste and dam construction methods

  • Mine waste consists of residues from mining – crushed rock mixed with water and chemicals from the extraction process. The slurry is pumped into large basins behind the tailings dams as a wet mass.
  • The upstream method builds the dam gradually upward by adding new layers on top of wet tailings. It's cheap, but the least stable and most prone to failure.
  • The downstream method builds new layers outward, on the dry outer side of the dam. This creates a broader and more stable base but is more expensive and requires more space.
  • The centerline method is a combination: new layers are placed directly on the dam crest, expanding the base partly outward. It's more stable than upstream, but less robust than downstream.

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Read the Norwegian version of this article on forskning.no

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