Pit & Quarry, February 2019
DRILLING BLASTING BLASTING MECHANICS REVISITED PART 2 OF 4 BLAST DESIGN STANDARDS Knowing how to control a blasts effects is critical for your operation Fortunately basic principles emerged more than 50 years ago to simplify setup BY ANTHONY KONYA AND DR CALVIN J KONYA 60 PIT QUARRY February 2019 pitandquarry com ISTOCK COM XESAI t is not just enough for one to understand what happens during a blast The most important thing to the average person is to know how blast variables can be controlled to suit the requirements of the operation In blasting a number of variables are easily under the control of the blaster including the burden spacing stemming subdrill and timing In order to simplify these dimensions ratios are created that could easily be understood and scaled to any operation In 1963 five key ratios were presented that could be applied throughout surface blasting conditions to give comparisons between multiple types of operations Richard Ash denoted these as k factors which were the starting point for simplistic blast design These could easily be used to get approximate starting points for various situations The ratios are presented below with updates for modern day understanding 1 Burden ratio KB This is the ratio of burden in feet to the diameter of the explosive in inches due to the fact that typically the burden will be scaled based on the diameter of the explosive 2 Hole depth ratio KH This is what we understand today to be called the stiffness ratio of a blast and it is the ratio of the bench height of a blast to its burden 3 Subdrill ratio KJ This is the ratio of the subdrill compared to the burden 4 Stemming ratio KT This is the ratio of the stemming length compared to the burden of the blast 5 Spacing ratio KS This is the ratio of the spacing to the burden These ratios will be analyzed within this article in greater detail comparing what Ash wrote in 1963 to what we understand today BURDEN RATIO The most critical and important dimension in blasting is that of the burden The choice in burden will ultimately affect the entire performance of the blast This is due to the fact that the burden dimension is the first step to designing the proper confinement for a blast Should the burden be too large the explosive will never break the rock If its too small then the explosive will throw the rock across the pit I
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