Risk-based access control at Mount Isa Copper Operations

Mount Isa Copper Operations (MICO) is one of the oldest and deepest mines in Australia, comprising the largest underground network of mine development in the world. During the early operational years, ground support, particularly surface support, was not routinely installed. Although rehabilitation in recent years has drastically reduced the amount of tunnel without support, there remain tens of kilometres of excavation with limited to no ground support installed. In addition, older development was often mined within close proximity to unfilled or partially filled stopes and vertical openings. The voids pre-date modern 3D mine plans and scanning technology. Furthermore, access to the voids to conduct scans is limited, this results in an imperfect understanding of the void sizes and proximity to accessible drives. The lack of ground support and knowledge of void status poses significant ground failure risks at MICO. A significant increase in rock related near-hit incidents occurred during the second half of 2014 and the first half of 2015. A number of these incidents had the potential to cause severe or fatal harm. The incidents triggered internal investigations that aimed at understanding and reducing the ground failure risk. The outcome of the investigations was the creation of a series of interlinked systems, namely the tunnel condition risk assessment (TCRA), mine closure areas (MCA), ground awareness training (GAT), vertical opening pillar hazard assessment and control (VOPHAC), stope void review (SVR), manual scaling crews, fall of ground database and the quality assurance/quality control management plan (QA/QC MP). The individual components of the system are specialised and simple. However, the system is comprehensive and robust. Each of the components, as well as how they interlink, is discussed within this paper. The interlinked systems and practices provide controls and have proven to be effective at reducing the ground failure risks. Although the systems were developed at MICO, they have the potential to be easily adapted and utilised at other mine sites.