Long reinforcement strategies for underground mines

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The increased need for mineral resources has lead to the exploitation of deeper ore reserves and the use of mining methods with higher production rates. In these conditions, one of the main engineering challenges is to maintain the stability of underground excavations under difficult ground conditions. Rock instability is the biggest cause of injuries in underground mines and can result in the suspension and closure of mining operations. When the zone of failure in the rock extends deep inside the walls, traditional rock bolts are not adequate and the use of longer reinforcement units, such as cable bolts is necessary to support the excavation. Cable bolts are high capacity long flexible ground reinforcement tendons comprised of multi wire strand. Their performance has been mostly determined from laboratory tests and is difficult to extrapolate their results to field conditions. Cable bolting strategies are based on empirical methods that refer to ideal conditions, include only a few of the available bolt types and are not applicable to all the excavation walls. Instrumented cable bolts provide useful information of cable performance but are not fully integrated in the support design. Numerical modelling can complement instrumentation data to provide a rational and robust approach for developing cable bolt strategies. This requires that we have a good understanding of the behaviour of cable bolts and that numerical models can reproduce the explicit behaviour of various cable bolt types under different conditions. The proposed research program aims on improving our understanding on the behaviour of different cable bolt types through in-situ pull tests and field trials in entry and non-entry underground excavations. Field monitoring, including advanced 3D laser scanning methods, extensometers and instrumented bolts will allow to characterize the performance of different cable bolt types and configurations under different conditions in the field. Sophisticated 3D numerical modelling methods will be used to capture explicitly the performance of the different cables and the 3D zone of failure in different stages of entry and non-entry excavations. The program will build on my previous work on the use of instrumentation and advanced explicit modelling of the rock failure mechanism and the behaviour of reinforcement. It will allow to increase our knowledge on the in-situ mechanical behaviour of the cables. The results will provide improved guidelines and tools for cable bolt design and ultimately improve the safety and cost effectiveness of underground operations. The Canadian mining industry is a main contributor to the economic wealth of Canada and has a significant shortage of highly qualified personnel that can work in ground control. The program will contribute significantly to the training of graduate students who will gain theoretical knowledge and field experience applying fundamental principles to solve real problems at mines.