The burden is the distance from a single row to the face of the excavation, or between rows in the usual case where rows are fired in sequence. This distance can have a major influence on the results of a blasting operation, particularly in terms of its effectiveness and efficiency. Find in the following sections several consequences of excessive burden.
Improper fragmentation
It occurs when the burden distance is too large. This large distance reduces the power of the explosive energy, which leads to the appearance of oversized, unbroken boulders requiring secondary cutting.
Flyrock hazards
High burden reduces the coefficient of absorption of explosive energy by the rock. One of the direct consequences of this phenomenon is the appearance of flyrock, which poses a real danger not only to workers but also to equipment and infrastructure.
Impact on loading and hauling
We have already pointed out that too large a burden leads to the appearance of large blocks at the end of the blasting operation. This has a significant impact on the loading and transport of the blasted products, for example by increasing the waiting times for mining trucks.
Higher vibration and noise
Connecting this phenomenon to ground vibration, an excessive burden might result in additional energy being transferred to the ground as vibrations, which could harm adjacent structures and pose safety risks (Blair & Armstrong, 2001). Inadequate burden can lead to increased air overpressure and noise, negatively impacting the environment and nearby communities (Coyle, 2024). Conversely, excessive burden reduces explosive efficiency, resulting in wasted materials and higher operational costs (Coyle, 2024).
Incomplete detonation
Excessive burden can lead to incomplete detonation. According to (Onederra & Esen, 2003), 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 (T min) and is dependent on the burden mass, explosive and dynamic material response to the explosive stimulus. Generally, but not always, T min can be decreased by employing small burdens, using higher energetic explosives or a combination of both.
Reference
Blair, D. P., & Armstrong, L. W. (2001). The Influence of Burden on Blast Vibration. Fragblast, 5(1–2), 108–129. https://doi.org/10.1076/frag.5.1.108.3315
Coyle, K. (2024, July 22). Effect of Excessive Burden Distance on Blasting Result—Part 1. WipWare. https://wipware.com/effect-of-excessive-burden-distance-on-blasting-result-part-1/
Onederra, I. A., & Esen, S. (2003). Selection of inter hole and inter row timing for surface blasting- an approach based on burden relief analysis. Explosives and Blasting Technique, 269–275. https://espace.library.uq.edu.au/view/UQ:98536
