Block size estimation is required to optimize support design, to estimate volumes for rockfall catchment systems, and is an integral part of many rockmass classification systems. The most common problem with existing methods used to determine block size is that a single, representative "average" block is calculated. By using the average intensity and average fracture size in analyses, the possibility for large blocks to form is disregarded. Equally important may be the presence of zones comprised of very small blocks that cannot be supported in the same way that the average sized block would be. To attempt to incorporate the distributions of fracture sizes and intensities encountered in a rockmass, DFNs have been used to create block size distributions for a given set of parameters. This work compares existing estimators of block size to outputs from DFN modeling. A set of descriptive parameters are presented for block size distribution curves. Charts to estimate block size distributions for different geometries are presented.

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