The effect of corrosion on the performance of rock support and reinforcement in Australian underground mines has not been widely researched and is generally not well understood. This is despite the number of safety concerns and operational difficulties created by corrosion in reducing the capacity and life expectancy of ground support. This thesis aims to investigate corrosion and relate how the environmental conditions in Australian underground hard rock mines impact on the service life of rock support and primarily rock reinforcement. Environmental characterisation of underground environments was completed at a number of mine sites located across Australia. This provided an improved understanding of the environmental conditions in Australian underground hard rock mines. Long-term testing on the impact of corrosion on the load bearing capacity of reinforcement and support under controlled experimental conditions was conducted in simulated underground environments. Rock reinforcement elements were examined in-situ by means of overcoring of the installed reinforcement and surrounding rock mass. Laboratory testing of the core determined changes in load transfer properties due to corrosion damage. These investigations provided an excellent understanding of the corrosion processes and mechanisms at work. Corrosion rates for a range of underground environments were established through the direct exposure and evaluation of metallic coupons in underground in-situ and simulated environments. / It was found that the study of corrosion is challenging due to the time required to gather meaningful data. In particular, the wide range of materials that comprise ground support systems means that it is impossible to examine all the possible combinations of variables and their potential influence on the observed levels of corrosion and measured corrosion rates. Despite these challenges, the systematic investigation has resulted in new corrosivity classifications for both groundwater and atmospheric driven corrosion processes for various reinforcement and support systems used in the Australian underground mining industry. Previous corrosivity classifications were not found applicable. Furthermore, these new corrosivity classifications are simpler than previous classifications and corrosion rates may be predicted from readily obtained measurements of ground water dissolved oxygen and atmospheric relative humidity. Different types of reinforcement and surface support systems have been rated with respect to their corrosion resistance and estimates have been made for the expected service life for various rates of corrosion.

Instability in stope panels in shallow mines manifests itself as rockfalls from the hangingwall. Rockfalls from unstable stope panels vary in size from rockfalls between support units, to rockfalls spanning between pillars or solid abutments, to rockfalls bridging several panels and pillars. A suitable and reliable design methodology for stable stope panels at shallow depths is therefore required. This methodology must consider all manifestations of instability in stope panels and take account of the factors governing the stability. Very few mines design stope panels according to a systematic design procedure or methodology. Rock mass characterisation, estimation of rock mass properties, identification of potential failure modes, appropriate stability analyses and other elements of the rock engineering design process are often neglected. Instead, panel lengths are often dictated by the equipment in use and by previous experience under similar conditions. Consequently, unplanned stope panel collapses occur on most near-surface and shallow mines. Although these incidents often occur during blasting, they pose a major threat to the safety of underground workers and the economic extraction of orebodies. Hence, a rock engineering design methodology for the design of stable stope panels between pillars is of vital importance for optimum safety and production in shallow mining operations. Using the proposed design methodology, rock mechanics practitioners and mine planners should be able to identify and quantify the critical factors influencing the stability of stope panels. The critical factors should then be used as input to the design of stable stope panels that will provide the necessary safe environment for underground personnel working in stopes. It is concluded that the design of stable stope panels should be a process of defining the means of creating stable stope panels for the safety of underground workers and optimum extraction of the orebody. Therefore, a method is required whereby all rock properties, their variability, and an understanding of all rock mechanisms affecting the stability of stope spans are used as a fundamental base. A procedure for identifying the mechanisms and rock properties relevant to the specific problem is then required. In this way, existing knowledge should be used in an optimal way to design site specific stable stope spans. Hence, it is proposed that the design methodology for stable stope panels is a process consisting of the following steps: 1. Define objective. 2. Rock mass characterisation. 3. Estimation of in situ rock mass properties. 4. Consider an “ideal” stope panel. 5. Identification of potential failure modes. 6. Stability analyses. 7. Identify all significant hazards and assess the significant risks. 8. Geometric optimisation. 9. Determination of support requirements. 10. Design of support. 11. Evaluation. 12. Recommendation and implementation. 13. Monitoring of excavation and support behaviour to validate design and permit modifications. / Dissertation (MEng (Mining))--University of Pretoria, 2006. / Mining Engineering / unrestricted