Notch formation in vertical excavations in a deep hard rock mine and rock stabilization methodologies

Abstract

This paper presents details of the early to mid-stage deterioration in the form of notch growth of two 3 m diameter bored raises that were excavated and slashed to 7.8 m to serve as an internal shaft (winze). In addition, the long-term deterioration of a series of ore/waste passes that were excavated with the bottom-up Alimak methodology is investigated. These excavations were completed at depths between 1200 and 1915 m below the surface in a hard rock mine in Sudbury, Ontario, Canada. The ability to see a cross-section of fracturing around the bored raises while slashing into them and observing the progressive growth of fractures was critical for understanding the factors leading to deterioration. The Alimak-driven ore/waste passes were in an advanced state of deterioration, which provided a late-stage notch growth profile that could be compared with the notch growth observed in the bored raises. The methods used to support and stabilize these excavations are detailed; in addition, methodologies to prevent some of the deterioration from occurring are also presented. The findings of this work are useful for understanding the mechanisms driving brittle rock failure in deep mining and subsequently for minimizing or preventing the deterioration from occurring.