Integrated investigations on fracturing processes of highly stressed mine pillars

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Mining contributes significantly to Canadian economy. According to the Mining Association of Canada, mining industry directly employed over 373,000 workers across the country in 2015, and contributed over $56 billion to Canada's Gross Domestic Product (GDP). In recent years, as mines progress to deeper levels (>1.5 km), a more reliable and efficient design of pillars has become increasingly important. A pillar is defined as a column of in-situ rock left between two or more underground openings. Pillars are used in almost all underground mining methods to provide support to mine openings and maintain a safe and stable environment for mine personnel and equipment. A better understanding of pillar mechanics can have a significant impact on the safety of mine personnel as well as the financial benefits of the mines. Pillars can be of different shapes and sizes. The size of pillars, usually expressed as the width-to-height (W/H) ratio, serves as an important design criterion. Typical pillar W/H ratios range between 0.5 and 2.5.Current engineering approaches for pillar design include empirical formulae from data based on in-situ pillar performances as well as numerical modeling, where the rock mass strength is estimated using empirical failure criteria. It is hypothesized that these approaches do not properly estimate the pillar strength at great depths (>1.5 km) due to the following reasons: 1) empirical pillar strength equations came from a database that is not appropriate for pillar design in deep mines; 2) common empirical rock mass strength estimation approaches tend to underestimate the confined strength of massive to moderately jointed rock masses; and 3) common pillar strength assessment approaches based on numerical modeling do not consider mining-induced stress changes, and their influences on progressive rock mass fracturing and strength degradation. The proposed research program aims at developing methods to improve the current understanding of fracturing processes and failure mechanisms of highly stressed pillars in massive to moderately jointed rock masses, subjected to mining-induced stress changes and non-uniform loading conditions. This research program consists of two main components: 1) laboratory-scale physical modeling; and 2) advanced numerical modeling using three-dimensional discontinuum modeling approaches. The outcome of this research program will provide future engineers with tools for a more reliable and economic pillar design in deep mines. This will have a direct impact on the financial and safety performance of Canadian mining companies, and will provide valuable opportunities for the training of Highly Qualified Personnel (HQP).