Preconditioning blasting for rockburst control in a deep shaft sink

This paper details the preconditioning blasting strategy that was developed and used while sinking the third deepest shaft/winze in Canada in a brittle rock mass. The high-stress conditions presented at the construction site resulted in seismic activity, uncontrolled spalling, and rockbursting. For comparison, muck is thrown away from the face in a lateral development round, leaving the round partially unconfined, which allows for immediate stress redistribution when operators are not present. A vertical blast will fill the created void with broken muck, which confines the bench and inhibits stress redistribution from occurring. As confinement is reduced from mucking out the round, there is an increase in strainburst risk when operators are required to mark bootlegs and prepare for drilling/loading the next advance. Due to the nature of shaft sinking, which relies heavily on physical labor and handheld mining equipment, there is increased operator exposure to rockburst risk compared with mechanized mining. Therefore, preconditioning blasting becomes a critical control for managing high-stress conditions. There are limited guidelines in published literature for preconditioning blasting in shaft sinking operations and less evidence that preconditioning blasting is providing a benefit. Therefore, the preconditioning blasting strategy that was used for the shaft sink was entirely original and was optimized based on visual inspections and seismic monitoring. This method should be beneficial for managing rockburst risks in deep shaft sinking in future operations.