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The University of NSW (UNSW) has released new research warning that more accurate testing is needed to curb earthquake damage to tailings dams in Australia.
Tailings dams are embankment dams that can extend kilometres in length, made to contain and store by-products of mining operations after processing mined ore.
According to a Professor in Geotechnical Engineering at the UNSW School of Civil and Environmental Engineering, Adrian Russell, 25 per cent of international tailings dams failures are due to earthquakes.
“When tailings dam fails, it’s catastrophic. The amount of damage it can cause to the environment is unthinkable, not to mention the risk it poses to any civilians,” Professor Russell said.
“These structures can be huge, with embankments sometimes reaching 300 metres in height, so you can imagine the amount of tailings stored behind them.”
The US National Earthquake Information Centre logs the measurements of up to 20,000 earthquakes around the world each year, which equates to 55 a day.
Australia is impacted by an earthquake exceeding a magnitude of five or greater once every six months — sufficient enough to cause extensive damage to a tailings dam.
The tailings are contained behind the embankments and consist of ground rock and metals as well as toxic and radioactive chemicals.
What is the potential impact of earthquake dam failure in Australia?
The UNSW states that in Australia alone, 250 active tailings dams store the resources of Australia’s mining industry — one of the largest industries in the country.
Australia’s mining industry relies on the performance of these dams to keep operations ongoing, as well as protect the surrounding environment and its site workers.
Professor Russell highlighted that while some trailings storage facilities (TSF) might exhibit minimal damage, others can be catastrophic to the natural environment.
In 2019, the failure of a tailings dam at Brumadinho in Brazil killed 270 people and resulted in water pollution in the Paraopeba River, impacting communities 120 kilometres away.
“If a TSF failure has the potential for high or extreme consequences, then the TSF owners are mandated by dam authorities in their respective countries to conduct thorough stability assessments every two years,” Professor Russell said.
This was seen in NSW in 2018 when gold and copper mining giant Newcrest experienced a tailings dam failure due to a low-density foundation layer, which released 1.33 million cubic metres of materials into the environment.
In 2019, self-conducted assessments carried out by Rio Tinto, BHP, and Glencore resulted in high to extreme risks of tailings dam failures.
Tailings dams in WA, SA, the Northern Territory and Queensland have all been found to have the highest public safety risk in the case of failure.
Professor Russell has urged that TSF standards and regular testing should not be avoided and even be upgraded if Australia wants to steer clear of disasters like the Brumadinho dam event in Brazil
Moving forward
In Australia, one of the ways to assess the dams and the tailings they contain is through cone penetration testing (CPT), which enables geotechnical engineers to determine their properties and asses their strength and stability.
However, CPT results can often be difficult to interpret.
Previous research conducted by Professor Russell and his team empowered engineers to interpret CPT results in tailings when they have different varying states.
This includes when dams have a mixture of air and water or, in other words, when they are unsaturated.
“Prior to this research, engineers routinely and incorrectly interpreted the CPT results by assuming the tailings are fully saturated, which isn’t always the case,” Professor Russell said.
The findings from the study outlined how to use CPT results to determine the in-situ state of the tailings, which is extremely important in controlling how strong and earthquake-resistant the tailings will be.
In his latest research paper, Professor Russell shows practitioners how to estimate the post-earthquake strength of tailings when unsaturated, to rectify false assumptions around unsaturated trailings.
“This means engineers can use improved strength estimations in any earthquake stability assessment to accurately identify which TSFs are more at risk of failure,” Professor Russell said.
He said Australian cities were at a “high risk” because an earthquake would compromise old infrastructure made of unreinforced brick and masonry.
As such, he said, earthquake protection and mitigation standards needed to improve.
“The next generation of earthquake standards needs to move towards performance-based designs not only to protect life but also to reduce the significant economic losses resulting from direct damage and business interruption.”
