Pit & Quarry, May 2018
DRILLING BLASTING Without consideration of fragmentation throw and confinement rhythmic timing could produce much worse results than previous blasting practices concerns but to minimize the negative effects in the other aspects ANOTHER PRINCIPLE TO CONSIDER In addition the most basic principal of blasting confinement needs to be understood and not violated For example lets assume that a signature hole analysis was run and the minimum peak particle velocity would be with a rhythmic timing sequence of 3 milliseconds Lets assume the sequencing of the blast is kept the same as the previous blast example This would give a row to row timing of 6 milliseconds providing no relief to the second row Instead of reducing ground vibration it could increase ground vibration by as much as 500 percent due to the large increase in confinement How can this be approached In the first case lets assume the 3 milliseconds in rhythmic timing was okay with holeto hole and the mine would accept the decreased fragmentation and increased scattering Previously a 42 millisecond delay was an acceptable amount of relief for the row to row blasting This same or greater delay would be needed between rows This could be achieved by firing each row with 14 boreholes where each borehole was fired in the first row before the second row began to fire such as the second table see page 33 However this may still be much too fast hole to hole or even in the corners of the blast Still at least this timing sequence would keep the proper row to row delay It is important to note that the total time for the blast was cut into almost one third which can lead to other consequences The other method could be to look for alternative timing windows if enough holes cannot be fired to allow for proper release of confinement from previous boreholes firing Maybe a 3 millisecond delay rhythmic timing reduces the ground vibration by 50 percent of the previous Engineered for Accuracy B u i l t to Endure Trusted to Last WY15 Conveyor Belt Scale WY10 Conveyor Belt Scale HY15 Conveyor Belt Scale WF10 Weigh Belt Feeder Control Gates Data Collection Custom Weighing Metering Solutions For the most demanding applications tecweigh com 8005364880 32 PIT QUARRY May 2018 pitandquarry com
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