Rockbursts: How Queen's engineers are working to make mining safer
The Ontario Ministry of Labour identified rockbursts as one of the top workplace hazards for miners in a 2015 report on mining health, safety and prevention. Lindsay Moreau-Verlaan, a part-time PhD student and full-time ground-control engineer at Vale’s Garson Mine in Sudbury, is working with two other Queen’s graduate students on an innovative practical research project to help prevent or reduce the hazards of strainbursts (a type of rockburst) in Ontario underground mines.
Strainbursting is the unpredictable and often explosive ejection of rock from the faces, sidewalls or roofs of advancing tunnels in deep mines in hard rock. Strainbursts are particularly dangerous because miners work directly at the rock face or tunnel wall where activities, such as drilling, may trigger an event.
“Strainbursts are very serious seismic events that can be devastating when they happen, and workers have died as a result of them in Ontario mines,” says Moreau-Verlaan, who is conducting this research to improve mining safety under the supervision of Dr. Steve McKinnon, professor and Chair in Mine Design in the Robert M. Buchan Department of Mining.
The project’s main goal is to develop scientifically based, practical guidelines for Vale and other mining companies to reliably design destress blasting techniques to prevent or mitigate the risks of strainbursts in underground mining tunnels. Destress blasting is thought to alter the properties of the rock mass so that high stresses are reduced, thereby reducing strainburst risk. But the technique has been used for decades based solely on experience rather than evidence; industry standards vary widely, and some companies don’t use destress blasting because they don’t believe it works.
“The current design of destress blasting is entirely based on experience, and there’s no hard evidence to say whether it’s truly effective. This research will give us a better scientific understanding of how destressing actually works and allow us to gauge its effectiveness. With an improved understanding, I believe the design of destress blasting can be engineered to improve performance, reduce risk and increase worker safety,” says Moreau-Verlaan.
Her preliminary research findings suggest that microseismic data—measurements of vibrations through the rock mass—and open borehole observations may be practical, effective ways to gauge rock-mass response associated with strainburst risk.
“Seismic and borehole data could provide a guidance tool to help decide whether and when to apply destressing in specific situations. In upcoming field trials, we’ll determine whether these metrics can also be used to measure destressing effectiveness and design improved techniques,” she says.
Kris Gingras Little, who is completing his Master of Science (engineering) and works as an engineer for Imperial Oil in Calgary, analyzed data from 129 reported strainbursts at three Ontario mines over the past decade.
“About 40 per cent ofthese events occurred when workers were at the face drilling. As an engineer, I’d like to provide better science-based options to make decisions about using destress blasting and worker safety. If the destress blasting isn’t done correctly, it could increase the risk of strainbursting,”he says.
Andrew McDonald, a PhD student, analyzed case histories of strainbursts from Vale’s ground-control incident records to define categories of geological environments in which strainbursts occurred. He then identified a specific mechanism associated with several strainbursts at Garson Mine and a different mechanism associated with strainbursts at other mines.
“The idea would be to tailor your mitigation strategy to the rock mechanics and strainburst mechanism that present the highest risk for your area,” he says.
As a native of Sudbury, McDonald knows how much this research matters to people living and working in the community. His dad has been a mining engineer with Inco and Vale for almost 30 years, and his sister is a geologist at Vale’s Coleman Mine.
“The preventive goal of this project is really motivating for me. It’s important to think about the very real risks to the people working underground. We’re working on trying to reduce the risk and the danger to people,” he says.