Earthquake research shakes the integrity of dams

Did you know that the US National Earthquake Information Center records measurements of 20,000 earthquakes around the world each year – about 55 earthquakes per day?

A concern that most people may not immediately consider is the impact on tailings dams, which are some of the largest engineered structures on Earth, designed to store by-products of mining operations.

About once every six months, Australia is affected by an earthquake of magnitude five or greater – enough to cause severe damage to a tailings dam.

“Australian earthquakes are staggered, which means they occur at locations far from the margins of continental plates such as the earthquakes in Japan and California,” says Adrian Russell, professor of geotechnical engineering and future Australian Research Council Fellow at UNSW’s School of Civil Engineering. environmental engineering.

Just last month, parts of South Australia were hit by the biggest earthquake the state has seen in nine years when a 4.8-magnitude earthquake was recorded in the Flinders region. In 2021, Melbourne was hit by an earthquake in Port Phillip Bay, and aftershocks were felt as far away as Sydney.

Tailings dams may be at risk of failure

When an earthquake strikes, the risks to tailings storage facilities (TSF), often referred to as tailings dams, may not be forefront of mind.

Tailings dams are dams along embankments, sometimes kilometers long, that are constructed to contain and store tailings, which are by-products of mining operations after the mined ore has been processed. The tailings behind dams usually consist of ground rocks, minerals, and even toxic and radioactive chemicals.

Unfortunately, 25 percent of global dam failures are due to earthquake, says Professor Russell.

“One of the main priorities for the extractive and mining industries is to reduce the number of catastrophic failures of tailings dams,” he adds.

“When a tailings dam fails, it is catastrophic. The amount of damage it can cause to the environment is unimaginable – not to mention the risks it poses to any civilians.”

These structures can be massive, with bridges sometimes up to 300 meters high, so you can imagine the amount of junk stored behind them.

They need regular maintenance and monitoring to make sure the bridge is strong enough to hold the waste.

“Shaking an already marginally stable bridge may lead to failure and sudden release of residue.”

When a tailings dam fails, it can be disastrous. The Brumadinho Dam disaster, considered the worst industrial accident in Brazil, caused millions of tons of toxic waste to flow into the surrounding area. Image: shutterstock

The impact of a waste dam failure

In Australia alone there are about 250 active tailings dams. Given that the mining sector is one of the largest industries in Australia, the performance of these dams is essential to the safety of the operation, the civilians who work those mines, and the surrounding environment and communities.

There is a wide range of effects of TSF failure. When some TSFs fail, fortunately there is little damage, says Professor Russell.

In 2018, there was a TSF failure at the Cadia gold mine in New South Wales. The collapsed section of the bridge and the debris have not moved far enough to cause environmental damage or deaths.”

But failures can also lead to massive waste discharges into the natural environment, which can lead to deaths and serious economic losses.

For example, in 2019, the catastrophic failure of a tailings dam at Brumadinho in Brazil killed 270 people, and the resulting water pollution in the Paraopeba River affected communities up to 120 kilometers away.

“If a TSF failure has the potential for serious or extreme consequences, then TSF owners are mandated by their countries’ dam authorities to carry out comprehensive stability assessments every two years,” says Professor Russell.

“These standards and regular testing are important if we are to avoid a catastrophic failure like the Brumadinho dam disaster in Brazil in 2019.”

Measure the risk of potential failure

In Australia, one method of assessing dams and the tailings they contain is the cone penetration test (CPT). CPT enables geotechnical engineers to define their properties and evaluate their strength and stability.

The test typically involves driving a vertically inclined conical rod into the embankment or tailings at a constant rate of penetration. During this process, measurements are made to collect cone tip resistance data.

Previous research by Professor Russell and his team has enabled engineers to interpret CPT results in tailings when they have different states, including when they have a mixture of air and water in the pores, or in other words, when they are unsaturated.

Findings from that study showed how CPT results can be used to determine the in situ state of tailings—which is very important because it controls how strong and earthquake-resistant the tailings are.

“Prior to this research, engineers routinely and incorrectly interpreted CPT results by assuming that residues were completely saturated, which is not always the case,” says Professor Russell.

“This led to incorrect determinations of the state of the residues at the site and an overestimation of the force.”

In his latest paper, Professor Russell and his team show practitioners how to estimate the post-earthquake strength of tailings when they are unsaturated.

“The CPT interpretation methods and strength assessments used in industry were developed prior to these discoveries mainly for saturated natural soils,” says Professor Russell.

“There are many differences between the natural saturated soil and the tailings in a dam, the tailings being more silty, more dust-like, and unsaturated in many cases.

“This corrects what many assumed wrongly: that unsaturated residues do not leach out in an earthquake. This means that engineers can use improved strength estimates in any earthquake stability assessment to determine which TSF factors are most at risk of failure.”

I look forward

The Australian National Commission on Large Dams (ANCOLD) stresses the risks of TSF failure in Australia. It requires that all high-consequence-class TSFs remain safe even after shutdown, and be able to withstand one earthquake in 10,000 years.

Professor Russell says the damage is not just tailings dams. Reinsurers rate the earthquake in Sydney among the top 20 risk exposures worldwide.

“Australian cities are at great risk because an earthquake would damage old, unreinforced brick and masonry infrastructure,” he says.

“Also, there are vast areas in Australian cities under which soil may experience a loss of strength and turn into a fluid-like state, or liquefy, in the event of an earthquake.

“Botany Bay is a particularly high risk area where the major ports are located. If an earthquake liquefies the land around Botany Bay, widespread damage could result, as the infrastructure becomes beyond repair.

Furthermore, the land may become uninsurable. The next generation of earthquake standards needs to move towards performance-based designs to not only protect lives but also reduce significant economic losses from direct damage and business interruption.”

Professor Russell’s work forms part of TAILLIQ (Liquidation of Waste), an Australian Research Council (ARC) connectivity project supported by financial and in-kind contributions from Anglo American, BHP, Freeport-McMoRan, Newmont, Rio Tinto and Teck. The TAILLIQ project is being implemented at the University of New South Wales in Sydney, the University of South Australia, the University of Western Australia (lead organisation) and the University of Wollongong. The work also forms part of the ARC Future Fellowship (FT200100820).

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