Abstract
Longhole open stoping is an underground mining method commonly used in Canada. Operational safety combined with low cost and high recovery have led this method to be widely adopted in underground metalliferous mining. The method is applicable for moderate to steeply dipping orebodies. While longhole open stoping is generally not a selective method, the stope boundaries are designed to minimize dilution while maximizing ore recovery.
A key measure of longhole open stoping performance is stability. Longhole open stope stability analyses can be divided into two categories: 1) geomechanic analysis of the stope boundaries focused on in-situ conditions, and 2) damage potential imparted onto stope boundaries by the longhole blast design. While the former deals with site characterization, stope sizing, and extraction sequence impacting stability; the latter considers energy imparted onto the stope boundaries by the blasting itself, which may also negatively impact stability.
Historically, stope stability analysis has focused primarily on geomechanic elements and rock engineering design approaches. Rockmass data collection, empirical stope stability charts, cablebolting designs, and numerical stress analyses are all common tools and techniques used to design for stope stability. However, even with robust, technically sound stope stability design campaigns, stope destabilization and overbreaks continue to be a frequent mine production challenge. Often, these stope instabilities arise from unfavourable blast-induced energy imparted to the surrounding rockmass, especially in the immediate hangingwall. Stope blast designs often focus on achieving full ore recovery and/or a required fragmentation profile, however minimal considerations are given to the stability impact of the blast design itself.
To further reduce the potential for stope instability, the stope design process requires assessment of blast-induced rockmass damage potential. There are multiple blast design parameters capable of triggering excess rockmass damage and impacting stope stability. Drillhole placement, hole size, hole burden, ring spacing, explosive type, and initiation sequence are just a few examples of design parameters that can be gauged, assessed, and refined to limit blast-induced rockmass damage and control stope stability. An engineered process to assess and refine blast design parameters for stope stability optimization is proposed.
Through provision of a case study, an example stope design process benefiting from blast design refinement to promote stope stability will be described. The case study will describe influencing parameters in the blast design and highlight techniques to gauge damage impact. Subsequently, blast design refinement opportunities targeting stope stability will be described. In conclusion, the content will motivate a broader perspective on stope stability design, incorporating design consideration particular to both the geomechanic elements and the blast design parameters.