Rockburst management in Canadian hard rock mines

Rockburst is a complex mining-induced phenomenon that remains difficult to be quantified. In particular, geological conditions contributing to rockbursts are more variable than those in many conventional engineering approaches. Faults, intact rock properties, and other rock mass conditions vary, sometimes, within small distance. Stress levels that store energy or drive structures can change with geological complications. For example, faults may channel stress between the void and the discontinuity, and/or alter the local stress direction. High-strength rock masses may be very massive at shallow depth, allowing for large/stable excavations. The same rock type may store excessive strain energy at depth or high mineral extraction, and lead to rockbursts. More robust ground support systems that can bear dynamic loading are now commonplace in mining industry. A typical approach would be able to evaluate rockburst potential, and selectively deploy more robust ground support systems. Rockburst resistant support is more expensive in installation than most support systems designed for gravity loading. Thus, an excessively conservative risk assessment can affect both direct support costs and productivity. As mines continue to go deeper, selective use of burst-prone support may not be an optimal choice, and pervasive installation may become necessary. This implies a need to maintain a reasonable installation speed, and the time to get to deep orebodies is a major economic factor. This paper shows field examples of rockbursts to highlight some of the complex issues related to the rockburst. A multi-tiered risk mitigation approach is used for rockburst conditions. Examples of risk reduction strategies are given and some examples from a deep hard rock mine are used to illustrate the relative success of the strategies. Given that some residual risks to worker safety remain, discussion is presented on where more research or process improvements would be beneficial.