Effect of Excessive Burden Distance on Blasting Result – Part 1

Excessive burden in blasting refers to having too much rock mass in front of the blast holes. This is relative to the designed blast parameters. The burden is the distance between a blast hole and the free face.

If this distance is too large, it can significantly impact the efficiency and effectiveness of the blasting operation. Here are some effects and consequences of excessive burden:

1. Incomplete Fragmentation:

When the blast design has too much burden distance between rows, the explosive energy may not be sufficient to break the rock effectively, leading to large, unbroken boulders or slabs.

2. Higher Vibration and Noise:

Relating ground vibration to this phenomenon, excessive burden can cause more energy to be transferred to the ground as vibrations, potentially causing damage to nearby structures and creating safety hazards (Blair & Armstrong, 2001).

On the other hand, inadequate burden can result in higher levels of air overpressure and noise, affecting the environment and nearby communities.

It’s worth noting that when there is excessive burden in blast design, the energy from the explosives is not used efficiently, leading to wasted explosive material and higher operational costs.

3. Flyrock Hazards:

Excessive burden can cause unpredictable flyrock, posing significant safety risks to workers and equipment.

4. Inefficient Loading and Hauling:

The resulting muckpile from an overburdened blast may have uneven fragmentation. This makes it harder to load and transport the material efficiently.

Increased Risk of Misfires:

5. Incomplete Detonation:

Excessive burden can cause incomplete detonation of explosives. This leads to misfires and the need for re-blasting, which adds to safety risks and costs.

Concluding Key point From Onederra and Esen’s conference paper at 2nd world conference on explosives and blasting technique in 2003:

In there paper, they stated that there is usually a discrete element of time that has elapsed from the time of explosive detonation to mass burden displacement. This time is designated as the minimum response time (Tmin) and is dependent on the burden mass, explosive and dynamic material response to the explosive stimulus. Generally, but not always, Tmin can be decreased by employing small burdens, using higher energetic explosives or a combination of both.

References

Blair, D. P., & Armstrong, L. W. (2001). The influence of burden on blast vibration. Fragblast, 5(1-2), 108-129.

Onederra, I., & Esen, S. (2003). Selection of inter-hole and inter-row timing for surface blasting—an approach based on burden relief analysis. In Proceedings of the 2nd world conference on explosives and blasting technique, Prague. Taylor & Francis (pp. 269-275).

Read more – Part 2: https://wipware.com/effect-of-excessive-burden-distance-on-blasting-result-part-2/

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