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Cave mining methods are becoming the methods of choice due to their potential to extract ore from large low-grade deposits at depth at production rates comparable to open pit mines. However, the high upfront capital related to the degree of development and time lag before production require detailed planning and reliable studies to cope with the associated risks. One important geotechnical issue is managing rock mass fragmentation that affects both project value and safety.
Both the scale of the problem and the lack of direct access to the rock mass at project evaluation and design stages make characterisation and accurate prediction of rock mass fragmentation a very difficult task. In this context, caving geomechanics is still largely an empirically based exercise. The discrete fracture network (DFN) approach uses fracture data collected from mapping of boreholes and rock exposures. The DFN approach was used to generate an in situ fragmentation model for the New Afton B1 Cave. The volumetric fracture intensity value (P32) is used as an indicator of the rock mass’s structural character, and provides a direct link to rock mass fragmentation. Major structures were included in the model and the spatial variability of the fracture intensity was analysed to derive a geostatistical model of rock mass fragmentation. The fragmentation ‘block model’ was then superimposed onto New Afton’s PCBCTM historical draw schedule model in an attempt to report blocks, representing the in situ fragmentation to drawpoint with respect to historical logs of hang-up event frequency, which also can refer back to height of draw (HOD). It was found that the influence of natural fractures diminishes gradually as the HOD increases. This is largely due to comminution in the draw column. The results showed that the model could identify areas of high hang-up events during initial draw prior to the column reaching maturity with respect to fragmentation.
Keywords: caving operation, fragmentation, discrete fracture network, hang-up event, height of draw, piecewise linear interpolation, fracture frequency
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