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• Using true spacings, all three-set block-forming combinations of S1, S2, S3 and S4 were <br />The results of this analysis, in the form of a cumulative probability distribution, are <br />presented in Figure 3-1, together with the cumulative distribution of block sizes from the <br />boulder catalog. The results are in good agreement, and converge well in terms of the <br />larger block sizes. Based on this analysis, a worst case block size of about 6000 cubic <br />feet is considered appropriate for rockfall hazard assessment. An 'equivalent' disk, with a <br />diameter of 26 ft, a thickness of 11 ft, and a volume of 5840 cu.ft. was used in the CRSP <br />runs described in Section 3.3. In the boulder catalog, blocks 620 and B49 have similar <br />dimensions and volumes. <br />analysed to obtain the frequency distribution of resulting block sizes. Experience has <br />shown that many discontinuity sets have a spacing distribution which approximates <br />reasonably to a negative exponential form (Priest and Hudson, 1976, Priest and Hudson, <br />1981), and this was assumed to apply in the present case. The negative exponential <br />distribution is asingle-parameter distribution which is completely defined by its mean, so <br />provided the mean spacing is known, the full range of probabilities can be estimated. <br />Analysis of the bedding plane data indicated a log normal spacing distribution. Using <br />these distributions, the potential discontinuity combinations and resulting block sizes were <br />analysed using probabilistic modelling software. <br />3.2 Model Calibration and Parameter Selection <br />Prior to the main hazard assessment, a number of trial runs were carried out to calibrate <br />the CRSP model, and select appropriate site-specific slope surface parameters. These <br />calibration runs were carried out on sections of the slope where previous rockfalls <br />provided a basis for comparing observed and predicted behavior. <br />• Typical block sizes were determined from the boulder catalog for each calibration section. <br />These block sizes were converted to equivalent disks or cylinders for input to the CRSP <br />is <br />