Strainburst potential identification and support of stress-fractured ground

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Despite the current financial constraints, the mining sector is growing, likely with a long cycle period, creating a unique economic opportunity for Canada to expand its mineral production. Finding a new ore body, however, takes years and getting a new mine permitted and operational typically takes 8 to 15 yrs. Hence, it is most attractive to expand the mine life by going deeper. Unfortunately, mining at depth is more costly and investors are only willing to commit capital if a project can be executed at low risk to workers, investors, society and the environment. This research focuses on the first two aspects. The stakeholders, as recipients of research, have identified two geomechanics aspects needing funda-mental and applied research: (1) Assessment and mitigation of risk from strain bursting; and (2) design of support for highly stressed (fractured) ground for optimal constructability to achieve high rates of ad-vance. Both are key elements of ensuring reliability in production at depth. The proposed research deals with challenges identified through recent experiences from deep under-ground construction and mines. Based on field observations, two key deficiencies in current rock engi-neering are identified: (1) Strainburst potential identification – standard approaches for rockburst assessment and support design are based on the premise that the damage causing energy comes from a seismic event (fault slip). This approach ignores the energy stored in near the excavation and thus is highly deficient. Furthermore, the potential location for strainbursting is hypothesized to be related to the potential for localized defor-mation. IF validated, progress will be made in creating safer work places through strainburst potential identification methods. (2) Support of stress fractured ground – at depth it is impossible to mine without creating a skin of stress-fractured ground around an excavation. Because of the hard rock nature of the rock at depth, this fracturing process is associated with geometric volume increase, called bulking, that impose severe strains on support systems. Current design approaches based on force equilibrium or energy dissipation equilib-rium is inadequate and the proposed research will develop deformation-based support design procedures. The rock fracturing process needed to better identify both strainburst potential and bulking properties will be assessed and respective ground characterizations techniques will be improved. The research, involving fundamental studies, field monitoring / observations, and back-analyses, will develop means to properly characterize rock at depth for strainburst potential identification and support design. The proposed research is unique in that underlying hypotheses have been identified and verified qualita-tively such that industry is willing to fund the installation of monitoring equipment to provide the data for this research. The potential value of the research findings, when implemented into mining operations, is substantial. While hard to quantify, it is estimated to contribute in the hundreds of millions of dollars to the bottom line of a single operation. It will assist in creating safer work places, in reducing investor risks, reducing rehabilitation costs, reducing production delays, and possibly in reducing ore loss. One industry repre-sentative suggested that the potential value of the proposed research program could be in the billion dollar range.