Stability analysis of ore pass systems at Brunswick mine

Ore pass systems are used in mines to transfer broken material from one mine level to a lower level using gravity. The integrity of ore pass systems can be compromised by changes in stress and the presence of fractures in the rock mass. Ore pass walls can also be damaged by the impact loads of rock fragments passing through an ore pass. Blast-induced damage for removal of material hang-ups in an ore pass can also contribute to ore pass wall degradation. A review of the pertinent literature on ore pass degradation suggests that all these failure mechanisms can potentially act simultaneously although one mechanism is usually the most dominant. The majorities of studies, addressing ore pass degradation, have either investigated the influence of only one failure mechanism or have not taken into account the full interaction of the different failure mechanisms. The objective of this thesis was to analyze the stability of ore pass systems at Brunswick Mine. A comprehensive ore pass data collection campaign was undertaken at the mine site. A qualitative and quantitative analysis of the collected data allowed the identification of current and past ore pass practice at the mine. This analysis focused on the influence of ore pass geometry and configuration, rock mass and stress regime and practice on the observed ore pass operational problems. Ore pass systems that reported significant signs of degradation were selected for further study. In particular the evolution of degradation was documented and the critical degradation mechanisms identified. A multi stage numerical approach was used to investigate stability of ore pass systems. The applied approach addressed the interaction of stress, rock structural defects and material flow impact as ore pass degradation mechanisms. The first element of this approach was the use of 3D stress analysis models using the Map3d stress analysis software package to calculate the global stresses. The second stage was the construction of a synthetic rock mass model to simulate the behavior of a fractured rock mass. Fracture-SG software was used to generate fracture systems similar to those observed at selected sites at Brunswick Mine. The fracture system models were then embedded into a three dimensional distinct element model, Particle Flow Code (PFC). The PFC simulates intact rock material as a dense pack of uniformly size distributed spherical bonded particles. A synthetic rock mass model can be subjected to different levels of stresses in three dimensions which depending on the stress level imposed, the synthetic rock mass can fail by fracturing through the intact rock matrix or by sliding along the pre-existent fractures. This is an important innovation in fractured rock mass simulation. The synthetic rock mass approach was employed for back analysis of an ore pass failure at Brunswick Mine. Using quantitative field data collected for a massive sulphide rock mass at the mine, a fracture system was generated using Fracture-SG. The incorporation of the fracture network geometry into a Particle Flow Code (PFC) resulted in a synthetic rock mass. The PFC model was calibrated to the mechanical properties of the massive sulphide