Organization: The Australasian Institute of Mining and Metallurgy

Pages: 10

Publication Date:
Jan 1, 1990

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Abstract

The standard charge weight scaling laws imply that only one particular delay (that possessing the maximum instantaneous charge) contributes to the ppv. However, the present analysis clearly demonstrates that a varying number of blastholes contributes to the ppv. This number also increases with distance, x, between the blast source and the detector, and is caused by waveform broadening due to attenuation. Thus the operative charge weight, itself, is also a function of the distance, and so makes the standard charge weight laws difficult to implement. If the delay time scatter is neglected, then, under certain conditions, relatively simple expressions can be derived for the ppv magnification, FN, as a function of the number, N, of blastholes. When the influence of delay scatter and random fluctuations in each blasthole vibration is included using Monte Carlo simulations, then, to a first approximation, the condition FN=KNx applies, where KN is a constant dependent upon N. Unfortunately, however, for any particular blast this condition cannot be distinguished from the standard charge weight scaling law. The dependence of ppv on N would only be apparent if blasts of differing N were to be compared in an otherwise identical environment. Since this situation is very difficult (if not impossible) to realise, then the influence due to N, although significant, goes largely undetected. Another problem associated with standard charge weight scaling laws is the difficulty of accurately assessing the appropriate charge weight, even if attenuation broadening is neglected. For example, if a number of blastholes are very close, then they experience a vibration interaction which is non-linear. However, if the same blastholes were to be widely spaced, then the separate vibration signatures add linearly. The standard charge weight scaling law fails to distinguish between such linear and non-linear regimes. Unfortunately, in many production blasts, both regimes exist throughout various portions of the blast spatial pattern and so makes it difficult to determine the operative charge weight. The solution to the combined influence of waveform broadening and linear/non-linear interactions will obviously require substantial future research. A possible solution may be found in the use of numerical dynamic codes. |

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