Joint project studies phenomenon of rockbursts

For centuries, one of the biggest dangers in mining has stemmed from the potential instability of the openings in which miners work. Often, the collapse of these structures is attributed to a phenomenon known as rockbursts.

Rockbursts are sudden, violent rock failures that liberate enormous energy, equal to up to 180 tonnes of TNT, creating earthquake-like vibrations. In the 1930s and 1940s, the Canadian mining industry built a wealth of knowledge and developed a strategy to avoid geological conditions which were prone to rockbursts. This strategy emphasized highly selective, sequential narrow-vein mining methods.

However, in the 1970s, as a result of pressure to improve its international competitiveness through increased productivity, the industry began converting to large-scale bulk mines. This involved increasing the size of mine workings, as well as the risk of increased rockburst activity. In 1984, under the leadership of the Canada Centre for Mineral and Energy Technology (CANMET), the main research and technology arm of Natural Resources Canada, the Canada-Ontario-Industry Rockburst Project began. Its mandate was to learn as much as possible about rockbursts and to translate this knowledge into safer, more economical mines.

Funded to the tune of $4.2 million by the partners on an equal basis ($1.4 million each from the Ontario government, the mining industry and CANMET), this initiative is managed by tripartite technical and management committees. The original project was scheduled to last five years but, because of its success, a second, 5-year phase was added and, currently, a further extension of the research phase is being considered.

“The purpose of the program is to understand rockbursts, to be able to predict and prevent them or, if we cannot prevent them, to at least control them,” explains Parviz Mottahed, manager of CANMET’s Sudbury laboratory. The first phase of the program (1985-90) concentrated on developing and installing the technology to measure seismic events and determine their location. The installation of seismic monitoring equipment and the interpretation of its data by software specially designed by CANMET employees allow scientists to determine the location, size and cause of seismic events in all of Ontario’s most rockburst-prone areas.

The provincial government, through its Ministry of Labour and Ministry of Northern Development and Mines, was responsible for providing the seismic monitoring equipment. The industry, through the Ontario Mining Association and the Mining Research Directorate (MRD), an independent body which co-ordinates and promotes research into underground ground control and rock mechanics, was responsible for in-kind services and the installation of the seismic monitoring equipment in Ontario mines.

By the end of phase one, the three partners had learned a significant amount about rockbursts and produced a 305-page book called “Rockburst Handbook for Ontario Hardrock Mines,” detailing this knowledge. Published by CANMET (in both French and English), it is considered the most complete work ever written in Canada on the subject.

As well, more recently, six of the CANMET employees most intimately involved in phase one of the project received special recognition for their contributions.

“Many people were involved in the program but these six in particular made it work and brought it to where it is today,” notes Mottahed. “They made a major contribution to the program and were among the early architects of the present program.”

The program is now approaching the completion of its second phase, building on the research of the first five years and concentrating on methods to alleviate rockbursts and limit their damage. This includes control methods, such as de-stress blasting to soften the rock and change the potential energy; altering the shape or orientation of development openings to minimize stress concentrations; studying support systems; and developing stiff engineered backfills and investigating other techniques to control or alleviate bursts.

“We are very good at locating a rockburst and we can easily say how big it was in terms of magnitude, but that doesn’t solve the problem,” Mottahed says. “Now we have to learn how to use this information to go from predicting a rockburst to preventing it, or at least controlling the damage.” Mottahed says an important aspect of the second phase is that the partners have invested significant sums of money — totaling about $10 million ($6 million from the mining industry, $3 million from CANMET and $1 million from the Ontario government) — and pooled it into one fund.

“Once we had the data collected, we knew we had to put in some hard cash to extend the research,” explains Charles Graham, MRD managing director. “To make the most of the money, we put it into one pot and proceeded with the research collectively.”

While CANMET manages the technical aspects of the initiative, the industry manages the financial aspects through MRD, which conducts research into a number of areas where partners share a common goal. MRD manages the rockburst program through a board of directors which includes company sponsors, federal and provincial representatives, and other interested parties such as unions, universities and research organizations.

Mottahed points out that the partnership base in the second phase of the program has been expanded, not just across Canada but internationally as well, with the inclusion of Codelco’s El Teniente copper mine in Chile. The Sudbury laboratory, officially opened in June, conducts research and development in three key areas: backfill, rockbursts and mine ventilation.