Pit & Quarry, May 2018
HOLE TIMING 17 42 THREE ROW PATTERN 238 ms 280 ms 322 ms 221 ms 263 ms 305 ms 204 ms 246 ms 288 ms 187 ms 229 ms 271 ms 170 ms 212ms 254 ms 153 ms 195 ms 237 ms 136 ms 178 ms 220 ms 119 ms 161 ms 203 ms 102 ms 144 ms 186 ms 85 ms 127 ms 169 ms 68 ms 110 ms 152 ms 51 ms 93 ms 135 ms 34 ms 76 ms 118 ms 17 ms 59 ms 101 ms 0 ms 42 ms 84 ms Times of holes firing in a basic 17 42 three row pattern In this sequence each hole in a row fires 17 ms after the previous hole and each row fires 42 ms after the previous row electronic initiation systems This may mean firing every blasthole 25 milliseconds apart but just incorporating this can have devastating effects on a site if not properly implemented To reiterate rhythmic timing practices must be implemented with the understanding of proper blast design Combining this with signature hole techniques regardless of the initiation system used can lead to predictions of the entire vibration waveform in the range of 90 to 95 percent accuracy with almost perfect prediction of the peak In addition to the errors listed in this article there is a large amount of material being published at explosive conferences by technicians that do not understand these basics of blasting This causes a great deal of confusion for mines everywhere For example using a signature hole Source Precision Blasting Services study with completely confined boreholes and attempting to develop an envelope or maximum peak particle velocity is against both practical and theoretical principals and should not be used An example of this may be using four or more boreholes with varied powder loads to vary the scaled distance and then predict that a certain area may receive up to 8 in per second Then when the shot is fired an actual vibration record of 3 in per second is picked up This is a completely inappropriate use of signature hole analysis and rhythmic timing techniques In addition to this it is common that when attempting to mitigate vibrational concerns and applying rhythmic timing practices a site will often sacrifice fragmentation and throw This significantly impacts the mine The goal then becomes not only to mitigate these vibrational CLASSIFYING www kpijci com pitandquarry com May 2018 PIT QUARRY 31
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