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Influence of stress, undercutting, blasting and time on open stope stability and dilution



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This thesis presents the results of open stope stability and dilution research which focused on evaluating and quantifying stress, undercutting, blasting and exposure time and their effect on open stope stability and dilution. Open stope mining is the most common method of underground mining in Canada. Unplanned stope dilution is a major cost factor for many mining operations. Significant advances in empirical stability and dilution design methods have improved our ability to predict probable dilution from open stoping operations. However, some of the factors that influence hanging wall dilution are either ignored or assessed in purely subjective terms in existing designs. This thesis attempts to quantify these factors, from a geomechanics perspective, to assist in predicting and minimizing dilution. A comprehensive database was established for this study based on two summers of field work. Site geomechanics rock mass mapping and classification were conducted and case histories were collected from Cavity Monitoring System (CMS) surveyed stopes from Hudson Bay Mining and Smelting Co. Ltd. (HBMS) operations. The stope hanging wall (HW) zone of stress relaxation was quantified based on extensive 2D and 3D numerical modelling. Stress relaxation was linked to the stope geometry and the degree of adjacent mining activity. The influence of undercutting on stope HW stability and dilution was analysed using the case histories collected from HBMS mines. An undercutting factor (UF) was developed to account for the undercutting influence on stope HW dilution. Numerical simulations were conducted to provide a theoretical basis for the undercutting factor. A relationship was observed between the degree of undercutting, expressed by the UF term and the measured dilution. Many factors can significantly and simultaneously affect a blast performance, which may result in blast damage to stope walls. Major blasting factors which influence stope HW stability were identified. The influence of blasting on stope HW stability and dilution was evaluated based on the established database. The HBMS database, Bieniawski’s stand-up time graph, as well as Geco mine case histories were used to evaluate the influence of exposure time on stope stability and dilution. Relating increased mining time to increased dilution allows the mining engineer to equate mining delays to dilution costs. Each of the factors assessed in this study was studied independently to assess its influence on stope dilution, based on the HBMS database. The factors influencing dilution often work together, so a multiple parameter regression model was used to analyze the available parameters in the HBMS database. The findings of this research greatly improve an engineer’s ability to understand and to predict the influence of mining activities and stoping plans on hanging wall dilution.



Stability, Open Stope, Undercutting, Stress, Blasting, Time, Dilution



Doctor of Philosophy (Ph.D.)


Civil Engineering


Civil Engineering


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