Day Two | Session Eight: Modelling
Abstract
The forecast of the size distribution of the fragmented rock, in the form as it will report at the draw points, is one of the relevant aspects to be studied for block caving projects and mines. Layout design and anticipation of secondary reduction necessities are key factors to which the fragmentation assessment is linked. In addition to the challenge of correctly characterizing the input geotechnical parameters for the fragmentation assessment, the fractions of interest are located at the extremes (tails) of the size distribution, where the coarser and finer block sizes occur. At the “tails” of the size distribution, data is scarcer, and statistics are more affected by random variations. Thus, the average and central tendencies of the distribution are of not much practical use. From the tools available for fragmentation assessment, the software BCF (Esterhuizen, 2003) has remained as one of the most used methods to estimate size distribution for block caving projects and mines.
In this presentation, the new DFN-BCF hybrid approach is described. In this updated method of fragmentation assessment, the generator of the primary block built into BCF software, has been replaced with a Discrete Fracture Network (DFN) model of the rock mass, making use of the full geometry of the relevant discontinuities that will drive the fragmentation process. Thus, the DFN model is used to obtain in-situ and primary fragmentation, while secondary fragmentation is calculated by splitting these blocks applying the BCF algorithm. Several DFN realizations are produced, to cover the whole distribution of fracturing intensity. The final product of the assessment corresponds to a weighted fragmentation curve, representing the whole rock mass to be caved, and its corresponding range of variation. It must be acknowledged that volumetric size distributions are not intuitive. To aid with the understanding of the results, a novel graphical output has been added to the assessment, consisting of a scaled graphical representation of the actual size distribution at the draw points using 3D spheres as a proxy of rock blocks volumes. In addition to the DFN-BCF method description and application, the issues related to the sampling of size distributions at draw points are briefly discussed. Up to date, the DFN-BCF hybrid approach has been calibrated and applied to two world-class block caving projects.
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