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Empirical methods form the basis of design for ground support and reinforcement of development at the Challenger Gold Mine (CGM) in South Australia. In a general sense, the rock mass conditions at CGM are very good. In situ rock stress is low relative to most Australian conditions with near hydrostatic conditions at a depth of 1,000 m, and the rocks themselves are strong and competent.
As a consequence of the generally favourable geotechnical conditions, the design of ground support and reinforcement for mine development areas is heavily reliant on the use of empirical methods. Detailed geological and geotechnical mapping is undertaken in all headings, and particularly at the site of proposed intersections. The rock mass is characterised using the Q-System, and various techniques are used to determine the appropriate assignment of the base parameters. As an example, rock quality designation (RQD) is interpreted from threedimensional contouring of diamond drill data and crosschecked against volumetric joint counts. Standard patterns for ground support and reinforcement are applied when the rock mass is characterised as ‘good’ or ‘fair’. Characterisation of the rock mass as ‘poor’ triggers site specific design to suit the prevailing conditions. All design is augmented by kinematic wedge analysis and geological observation.
Currently, CGM ground support and reinforcement designs target a Factor of Safety (FS) of at least 1.5 in static conditions with an overriding dynamic capacity in excess of 5 kJ/m2. In recent years, considerable effort has been placed on optimising the empirical designs while maintaining the overall integrity of the process. This has led to a significant reduction in use of consumables through the optimised use of geotechnical engineering.
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