Mine site rehabilitation taking cues from nature

World expert in tailings dam design, construction and maintenance Professor David Williams is pushing for a review of mine site rehabilitation engineering practices. It’s the latest in a series of stories with Professor Williams which addresses the need for improvement in tailings dam management. There were six tailings dam failures reported last year. In November a dam failure on the Petra Diamonds lease in Tanzania created a mud wave up to 1.2 km wide which travelled over 8 km, covering 5.09 square km, damaging 13 houses and farmland. Tailings dam failure at Petra Diamonds’ Williamson mine in Tanzania. The long-term rehabilitation of mines, including tailings dams, was an issue often addressed conventionally despite evidence the remediation was inadequate, Professor Williams said. The issue is ‘consequence’ and Professor Williams says a greater social awareness of the impacts of millions of cubic metres of toxic sludge on the environment now means the impacts are reflected on respective company share prices. This, the fourth in a series, looks at how better civil engineering can help future proof tailings dams. Tailings dam design is a vexed issue. A batter too steep will discourage runoff; too shallow it causes erosion and what engineer can plan for the effects of drought that kills ground cover and flood that takes whatever’s in its way? A tailings dam in the Gulf of Carpentaria, 500,000 square kilometres of which was covered in monsoon water in 2019? Forget it. But you can’t. Despite these challenges, current dam design was largely ‘back to the future’ and new thinking was needed to future-proof tailings dams and other mine site rehabilitation, Professor Williams said. “It's interesting that people revere nature, which is diverse,” Professor Williams said. “Diverse topography, concave slopes, gullies, ridge lines, different vegetation, and so on. "And yet, when we do rehabilitation, we tend to make it all the same slope … “I think we could do a lot better in terms of what many people call geomorphic design, a more natural landscape or landform, one that builds in bold gully features to take the excess flow and makes sure that they're well reinforced with rock and so on. Director of the Geotechnical Engineering Centre at University of Queensland, Professor David Williams “Don't let's defy nature. Let's work with it. Let's learn from nature and use nature as a guide to the sort of landform we could form from a mine waste facility, whether it's a waste rock dump or a tailings dam or whatever.” Professor Williams is advocating for more research on all levels including financing and management as well as design, construct and maintenance. “I think (there are) lots of things that we need to experiment with. I mean, it is the height of madness to keep doing the same old same old when we know it doesn't work. “And we've got a huge legacy worldwide and more particularly in, because we're talking about Queensland, the Bowen Basin for example, of unrehabilitated mined areas. “And the standard approach is to make them relatively flat, topsoil and put drains on, put contour banks on them, and expect that that will work. And the major cost of that is actually earthworks. “Now, I'd call it dumb earthworks because it's not very well directed. We should devote our attention more to constructing more sustainable in perpetuity-type landforms. And that can include steep slopes because nature does. And it should have concave slopes, not linear ones.” Abstracts are being called for the Australasian Institute of Mining and Metallurgy’s Mine Water and Tailings conference held in Brisbane July 14-16.

Mine site rehabilitation taking cues from nature

Industry Queensland

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