Riveting performance

1. Michael Tost, Professor for Sustainable Mining Technology, Montanuniversität Leoben, Austria
2. Philipp Hartlieb, Senior Scientist and Mining Engineer, Montanuniversität Leoben, Austria

By adding digital technology to a simple steel bar, these researchers are trying to make underground mining safer and sustainable

What aspects of sustainable mining are you focused on at the moment?

Michael: Our focus is on underground mining in Europe, where there is fierce competition for land that might be used for purposes other than mining – agriculture, for example, or tourism. We’ve already seen instances where existing open-pit mines were not allowed to expand, so we’re looking at how they might continue to operate as underground mines.

From an environmental standpoint, open-pit mines are generally considered less desirable than those underground. They use more land and have a bigger impact on it. In underground mines, by contrast, some waste material can be kept underground and used for backfilling – refilling an excavated hole – so you also need less land for waste disposal structures. From a safety point of view, however, underground mining could be seen as more risky.

In Europe, competition for land is pushing the industry in the direction of underground mining. At Montanuniversität Leoben, we are working on new underground mining methods that are more economic than current ones, and are focusing on particular aspects of digitalization.

What are some of the key technologies being developed?

Philipp: One technology we’ve been working on is a digital rock bolt.

When you mine underground, you need artificial support for the rock mass to stabilize it for a specified period of time. That can be two weeks or 200 years. You can simulate the load-bearing capacity of your support measures; and you can simulate the behavior of the rock mass to see whether it's going to break, or collapse. After that, you can generically install support measures. But you still don't have information about how the support measures really perform.

A rock bolt is a steel bar that is inserted and then tightened or glued into the rock mass. Rock bolts can be up to three meters long. Other support measures include wire mesh, which helps prevent rocks from falling, and shotcrete, which is concrete you spray on the rock wall to stabilize it.

Before you go into the mine, engineers will have checked for areas where you might expect to find instabilities. Among other things, they use something called measuring bolts. These bolts have no supporting capacity; they are just installed for measuring the behavior of the rock mass. The thing is, they’re pretty expensive: roughly 2,000 euros, or dollars, apiece. Because it comes at such a high cost, you tend to think very carefully before buying and installing something like that, and you only install them at very specific spots that you’ve identified beforehand.

We’re looking at ways to digitalize the standard rock support bolts by installing a cheap sensor on every bolt that would be installed anyway. This will allow us to analyze the behavior of each bolt. Mining engineers will then know how they are stressed, or how they are elongated if the rock mass is moving. You will know if one of them fails, so you can replace it. You’ll know whether to increase or reduce the number of bolts you install. You’ll know if you need to change the entire mining layout because the stress distribution of the underground structures is going in an unexpected direction. You have much more knowledge about the rock mass and the behavior of the underground structure.

To do all of that, you not only need the sensors, you would also have to set up a small communication network inside the mine, and appropriate capacities for the Industrial Internet of Things.

So are the digital rock bolts mainly for safety, or do they also help with sustainability and environmental protection?

Philipp: Both. Local failures identified by those rock bolts are more safety-related, and by local, I mean anything that takes place in a very confined area. But anything we observe as a global trend in the mining operation is more related to sustainability. That’s because we’ll be able to optimize the mining layout and the mining sequence in a way that allows us to get a greater quantity of valuable materials out of the mine, more efficiently and without compromising safety.

Michael: So, for example, you cannot extract 100% from a deposit with traditional mining methods. A good illustration is the mining method called “room and pillar,” where “rooms” of ore are excavated and “pillars” of unused ore are left in place to support the roof. Using that method, you might have to leave in place pillars that make up half of your deposit. But if you have better information about that mine, you can potentially reduce the size or number of your pillars. That means that, for any deposit of a given size, you might be able to extract significantly more ore. More efficient extraction helps sustainability.

Do these digital rock bolts exist now, or are they still being developed?

Philipp: They’re being developed. We have prototypes installed in some European mining operations, but we’re still working to produce an industrial-grade sensor-and-bolt combination.

Sounds like something every mine would want to have. Once you perfect the technology, do you expect it to become universal in the mining industry, or are there hurdles to broad adoption?

Philipp: Different mines have different scales. There are small quarry operations producing 500,000 tons a year, with two dump trucks and three or four excavators operated by about 10 people; then there are huge mines producing hundreds of millions of tons, with 20 of the largest trucks you can imagine, and associated auxiliary equipment. The approach of those two different types of mines will be completely different.

When you talk to a small-scale operation and say to them, “Let's digitalize your processes, then you’ll perform better,” they’re going to say, “I can’t optimize two dump trucks down to 1.8 trucks.” When you talk to a very large company, it’s different.

The second aspect is network connectivity. The mining environment is constantly changing over time, which makes it complicated to maintain the network. You need to maintain your power supply, and your supply of fresh air and water. You also need a 5G, Wi-Fi, or LoRa network. And with every piece or layer you add, you’re expending effort.

So, depending on the mining system you're using, you will need to consider whether it's worth the effort to install the digital rock bolts. That’s one of the major hurdles to adoption.

Is this something that's more likely to be adopted by larger mining companies, rather than smaller ones?

Philipp: Potentially, yes. But what we’ve also observed is that, if there is an interested engineer in a small operation, they tend to be extremely flexible. As a researcher, you can just go to them and say, “Hey, let us test something,” and they say, “Okay, let's do it.” In a big operation, by contrast, you need to go all the way up through management. But on balance, it’s probably more likely that a larger operation would adopt the digital rock bolts.

Were the digital rock bolts invented or developed by your university? Or are they being worked on by different researchers in different parts of the world?

There are different initiatives with different technologies. Eventually, we’ll see which one is most successful. The one I have in my hands here [holds up a steel bar] is something our university is developing together with a rock bolt manufacturer. The sensors were developed here at at our university.