Geotechnical Hazards in Deep Mines: Case Studies of Seismicity and Boundaries Changes

ABSTRACT: Seismic events and rockbursts are recurrent geotechnical hazards in deep underground mines with significant levels of stress and extraction. These hazards can be manageable if adequately addressed during the design and monitoring phase. However, changes in the geological boundaries can trigger a series of seismic events. Temperature fluctuations and the presence of water can alter the stress conditions, mechanical properties of rock mass and affect geological discontinuities. Two case studies are presented. The first case study focuses on seismicity induced by an underground fire in a deep-level gold mine in South Africa. The second case study investigates seismic events caused by water from backfill pouring in a deep-level copper/nickel mine in Canada. An analysis of the source mechanisms of these induced seismic events revealed that they vary from burst-type to slip-type seismic events. The significant seismic activity during sand fill pouring in the Canadian mine confirmed the high stress predicted by the numerical model (Deviatory Stress Ratio 0.5). The stress and past seismic events influenced ground support selection for rock burst-prone areas. 1. INTRODUCTION As mines deepen, geotechnical hazards become less forgiving, and companies must recognize that failing to identify and mitigate these in design and operational strategies could be catastrophic, resulting in significant mine underperformance or premature closure. The objective of these case studies, both in the gold and the copper/nickel mines, is to improve our understanding of the way the fluctuating temperature impacts the operations, and the presence of water can alter the stress conditions, mineralogy, and mechanical properties and affect the geological discontinuities in the deep mines. The geotechnical hazard results in rockbursts, which are more common in deep, hard rock mines and represent one of the most severe mining hazards affecting the operation's safety, economics, and productivity. The violent and unpredictable nature of these rockbursts makes them remarkably challenging to mitigate and control. The two studies presented below include a case study on seismicity induced by an underground fire in a deep-level gold mine in South Africa. The other case study investigates seismic events caused by water from backfill pouring in a deep-level copper/nickel mine in Canada.