Spacing example

Spacing with Delayed Holes


In this video Anthony Konya explains how to calculate spacing with delayed holes. Incorrect spacing can make blast vibration increase up to 500%! This happens in ground vibration when to much spacing is included in the blast pattern, as the hole will feel constrained and not break the rock effectively. When too little spacing is applied the air overpressure levels will be drastically increased.

In this picture below we can see what happens when spacing is too far apart. Here we can see that the back row of this blast has cratered, and left jagged edges on the face. This can be a potential problem in the next blast, and also for safety of personal and equipment that operate near the face. We can also see that their has been severe back break to the top of the wall. This is because of incorrect spacing!

Spacing example

Spacing is based on 3 unique factors: Stiffness Ratio, Timing, and Burden.

Here he have isolated the timing variable to be only blast in which each hole is on a separate delay.

In regards to stiffness ratio we classify benches as being high (S.R. is greater than or equal to 4) and low (S.R. is less than 4). We then have spacing equations for both of these situations.

Spacing is directly related to burden, in general you always want your spacing to be greater than your burden. This will ensure that your blast fires properly and rock is moved in the correct direction.

Spacing Equations

Low Benches (Stiffness Ratio less than 4)

Spacing (feet) = {Bench Height(feet) + 7 x Burden (feet)}/8

Spacing (meters) = {Bench Height(meters) + 7 x Burden (meters)}/8

High Benches (Stiffness Ratio 4 or greater)

Spacing (feet) = 1.4 x Burden (feet)

Spacing (meters) = 1.4 x Burden (meters)

Remember when designing your next blast that spacing is an extremely important variable that when not calculated right can drastically change how your blast will function.

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