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I posted this question in physics, but they advise me to post it here so here I am.

I was looking for the formula to calculate the burden in bench blasting and I found this document. The problem is I have to calculate the concentration of the charge first with the unit kg/m. I know that some materials are given but I need the formula to calculate other materials in which I have their energetic values calories/g calories/cm3 ..

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  • $\begingroup$ This document might be interesting: Explosive Engineer's Guide. $\endgroup$
    – Fred
    Commented Nov 9, 2023 at 6:19
  • $\begingroup$ My understanding is the charge concentration, I$_b$ is the mass of explosive divided by the length of hole that contains explosive. $\endgroup$
    – Fred
    Commented Nov 9, 2023 at 6:23
  • $\begingroup$ This seems to be a units issue, not an engineering issue. $\endgroup$
    – Solar Mike
    Commented Nov 9, 2023 at 6:42
  • $\begingroup$ @SolarMike: For those who don't know anything about explosives engineering & blasting, it's not a units issue. If anything, it's more of a terminology issue. The units at the end of the text are not important to what is being asked. $\endgroup$
    – Fred
    Commented Nov 9, 2023 at 9:05
  • $\begingroup$ @Fred sure it is terminology issue no doubte on that, so since it is mass per distance can it be the velocity or pressure? $\endgroup$
    – Tintin
    Commented Nov 9, 2023 at 16:28

1 Answer 1

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The charge concentration, in kilograms per meter of drill hole, serves two purposes. The first is being able to determine the amount of explosives needed to blast a given amount of rock. This is needed when ordering explosives from the supplier or when taking out enough explosives from the magazine.

$M_{Explosives} \ = \ I_b \cdot N \cdot (L_H \ - \ L_S)$

Where:

  • $M_{Explosives}$ is the mass of explosives required [kg]
  • $I_b$ is the charge concentration [kg/m]
  • $L_H$ is the length of the drill holes [m]
  • $L_S$ is the length of the stemming [m]
  • $N$ is the number of drill holes

The other purpose of the charge length is, if one knows the energy equivalent of each type of explosive [J/kg], for its given density of explosive, it becomes possible to calculate the amount of energy expended in the blast by the explosives used.

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  • $\begingroup$ first thank you for the time you have gived to answer my question i apreciate that, so lets say the material is TNT it has 1.65 g/cm3 and 4.184 MJ/kg can you please add that as an example in your answer thank you again. $\endgroup$
    – Tintin
    Commented Nov 9, 2023 at 21:30
  • $\begingroup$ When you say "The charge concentration, in kilograms per meter of drill hole" you mean X kilograms multipied by numbers of meters deep of the hole? For example if the charge concentration is0.3kg/m TNT and a drilled hole is 7 meters deep stemming excluded this gonna equal to 0.3×7 = ~ 2.1 kgs total per one hole. $\endgroup$
    – Tintin
    Commented Nov 10, 2023 at 14:13
  • $\begingroup$ @Tintin: Regarding your last question with a charge concentration of 0.3 kg/m & a 7 m long hole, yes the mass of explosive in the hole would be 2.1 kg. $\endgroup$
    – Fred
    Commented Nov 10, 2023 at 19:14
  • $\begingroup$ @Tintin: TNT is not a good example of an explosive to consider. It's basically a military explosive & rarely used for civil or mining purposes. It is mixed with other explosives as a compound, but I'm unaware of it being available as sticks. For surface mining & quarries ANFO or emulsion explosives are more likely to be used. $\endgroup$
    – Fred
    Commented Nov 10, 2023 at 19:21
  • $\begingroup$ Thank you very much Fred that was very informative. $\endgroup$
    – Tintin
    Commented Nov 10, 2023 at 19:40

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