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PRODUCTION BLASTING with respect to the maximum value obtained for selected blasts, irrespective of the delay time recorded. If each explosive charge in the blast were to yield the same specific energy (i.e., MJ/kg), as expected, all of the circles shown in the figure should have had the same radius, since there were no variations in explosive type or its diameter or its mode of intiation. However, as the figure shows there is considerable variation in specific energy release from the various explosive charges, with values ranging from 100% to total failure. For this study, a very conservative criterion of specific energy release is applied, i.e., 0% to 20% of the expected energy release (with respect to the normalized maximum particle velocity amplitude) considered a failure, >20% to <40% considered a partial energy release, and >40% to 100% considered full energy release. On that basis, only three holes in the blast appeared to release full energy, six only partial energy, and seven holes with negligible energy. Another way of illustrating the specific energy release figures for a number of regular stope blasts is shown in Figure 8. It shows 28 blast holes to release less than 20% of the expected explosive energy, and only 22 blast holes yield nearly the full energy (i.e., 40% to 100% of the expected energy). Figure 6—Comparison of resultant particle velocity from vibration record obtained from a typical production blast from both geophone and accelerometer stations at the same location. Discussion and Conclusion There is considerable data available in open literature on measurement and analysis of blasting vibrations from mining and quarrying operation. Much of this information, however, relates to estimation of damage potential to civil structures and to a lesser extent, to pit slope stability and blast-induced damage to rock mass, and detecting obvious misfires or firing time deviations in a blasting round. In contrast, near-field vibration measurements and their diagnostic use in examining explosive performance and blast design has received much less attention (Mohanty, 1997; Fleetwood et al, 2009). The results of this study show there is significant discrepancy between the expected vibration amplitudes in terms of specific vibration energy released and that actually measured in the stope blasts under investigation, all other conditions remaining the same. In this case, aside from the usual firing time deviations with pyrotechnic detonators, typically more than one-third of the blast holes release very little energy in the form of transmitted seismic energy over multiple accelerometer 56 E&MJ; • AUGUST 2013 Figure 7—Calculation of normalized explosive energy (i.e., energy in arbitrary units/kg of charge) in a production blast against the delay. The radii of the circles are scaled with respect to the maximum value of derived energy for any explosive charge weight in the blast in question. Figure 8—Specific explosive energy (i.e., seismic energy) distribution in a production blast from various explosive rounds. www.e-mj.com