Learning from nature in the design of tailings dams

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With the latest standards for tailings dams demanding a longer-term view of the results of design, construction and closure, there is a growing interest in design philosophies that incorporate forms and processes as they arise. exist in nature.

“The timelines for responsible post-closure mine management, including the ongoing risks associated with tailings dams, have gone from decades to centuries, if not millennia,” said Justin Walls, senior civil engineer in mine closure at SRK Consulting. “This change makes traditional maintenance techniques very expensive – perhaps unaffordable – and calls for a redefinition of how we design these structures in the first place.”

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Speaking at the recent conference of the Environmental Engineering Division of the South African Civil Engineering Institution (SAICE), Walls stressed the value of geomorphological designs that mimic natural landforms as an example of this trend. .

“Engineers and scientists are increasingly looking to learn from natural analogues, to understand how natural processes work in a sustainable ecosystem so that we can better mimic these more sustainable designs and structures,” he said. “With the recent rise in the bar by the Global Industry Standard on Tailings Management (GISTM), it is likely that these nature-based approaches will gain popularity. “

GISTM stresses that designing and operating for closure requires a long-term vision and that tailings facilities should be planned, designed, constructed, operated and closed on the assumption that they will be permanent landforms. It also stresses that short-term financial or operational priorities should not take precedence over better design and operational practices that would have lower long-term impacts, complexity or risks.

Walls notes that the impact of climate change is one of a series of “unknowns” that make it difficult for mining companies to fully predict how tailings pond designs will perform over a 100, 500, or 1 period. 000 years old. In the past, the designers of these facilities have developed complex scientific responses to a range of factors, including physical stability, water management, groundwater pollution, wind and water erosion, roofing materials. and vegetation establishment.

“Today we face many other unknowns whose impact will unfold unpredictably in the years and decades to come – from climate change and neighboring land use to changing regulatory requirements and evolving ecosystems. “, did he declare. “Many of the tough engineering solutions we’ve used in the past, which often require considerable ongoing maintenance, may not be optimal to meet future challenges. “

In light of this, he argued that designers are learning how nature itself creates balances in its ever-changing environment. When it comes to water flow, for example, natural systems tend to store water more easily and release it more slowly, while traditional engineering typically focuses on man-made channels to speed up drainage. of the system water, resulting in high speeds. Waste rock dams are generally designed to maximize their storage capacity while minimizing their footprint, which is usually achieved by having steeper side slopes – while nature favors slightly wavy shapes with less angularity.

“By designing from scratch for a more geomorphic result, it’s easier to incorporate features like storage and release covers on tailings dams, for example,” he said. “It can use water more efficiently to support the growth of sustainable ground cover, while reducing the need for irrigation.”

Such an approach could also help introduce redundancies in the design, in order to mitigate the impact of extreme precipitation events – which are becoming more and more common. This would improve the ability of a tailings facility to cope with severe storms. There is also more emphasis on biodiversity on the cover of waste rock dams; much effort has been invested in finding plant species to be grown on tailings dams, with varying degrees of success. A nature-based approach prioritizes the need for complex, biodiversity-rich ecosystems for long-term sustainability.

“Another area of ​​study is how the soil structure on tailings dams can provide better conditions for plant growth,” he said. “It builds on agricultural and soil science and moves away from strategies like compaction to stabilize these structures. “

GISTM stressed the need to begin planning for tailings dam closure much earlier in the life cycle of the facility. By the time mines present a detailed design for a new tailings dam, they must have a pre-feasibility closure design in place. SRK Consulting has previously been engaged to provide such closure engineering inputs to a GISTM compliant tailings dam design for a southern African mining company.

“This type of intervention is going to prove very useful in reducing future liabilities,” said Walls, “and could involve considering a range of options ranging from flatter slopes, different types of soil, better water management and the shape of the top of the structure. “

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