Why do dams collapse?

Knowledge gaps and management shortcomings contribute to the catastrophic failure of tailings dams and ash ponds that claim thousands of lives around the world, according to three international scientists.

The latter problem is all too obvious. 

Analysis of case histories “points to sub-standard management and operational practices, often driven by the pursuit of greater financial returns”, they say, noting that when the Paris-based International Commission on Large Dams investigated 221 incidents it concluded that most were avoidable.

The knowledge issue is a little more complex, however.

In a “Perspectives” article in the journal Science, Carlos Santamarina, from the University of Science and Technology, Thuwal, in Saudi Arabia, Luis Torres-Cruz from South Africa’s University of the Witwatersrand, and Robert Bachus from Geosyntec, US, highlight how little is understood about key processes that cause and are caused by dam failures. 

“Filling these knowledge gaps will require changes in how coal ash and mine tailings are characterised, improved test protocols, and enhanced physics-informed data interpretation,” they write. 

The failure of a tailings dam which killed 223 people in Brumadinho, Brazil, in January 2019 would appear to be a tragic case in point.

The dam collapsed three years after it had been closed – contrary to expectations that geotechnical structures become more stable with time – and less than six months after an audit concluded it was safe.

The authors say an important but often unrecognised point is that the fast-moving and deadly mudflows that frequently follow dam failures usually do not cause them.

“This liquefaction of the impounded materials may suggest to regulators and the public that the problem lies with the impounded materials themselves,” they write. 

“However, in the absence of internal collapse or induced shear (for example, as a result of a seismic event), liquefaction and outflow of ponded ash and tailings occur after the dam has failed.”

Understanding the specifics of each failure is complicated by the fact much of the evidence is watched away, but the scientists say forensic investigations of notable disasters have identified several mechanisms and “often found the convergence of more than one weakness in the design, construction and/or operation of the dam”.

The full article can be read here.

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