Question

What is the primary mechanism by which stemming length affects blast fragmentation and airblast overpressure?

Accepted Answer

The primary mechanism by which stemming length affects blast fragmentation and airblast overpressure is its ability to contain the explosive gases generated during detonation within the borehole, allowing them to perform useful work in fracturing the rock. Stemming is the inert material (typically crushed rock or drill cuttings) placed in the borehole above the explosive charge to confine the explosive energy. If the stemming length is insufficient, the high-pressure explosive gases will vent prematurely from the borehole, reducing the energy available for rock fragmentation and significantly increasing airblast overpressure. Airblast overpressure is the pressure wave generated by the sudden release of explosive gases into the atmosphere. With adequate stemming length, the explosive gases are contained for a longer period, forcing them to expand and exert pressure on the surrounding rock, creating fractures and fragmenting the rock mass. This confinement also reduces the amount of gas released directly into the atmosphere, thereby minimizing airblast overpressure. Conversely, if the stemming is too short, a significant portion of the explosive energy escapes as airblast, resulting in poor fragmentation and potentially causing damage to nearby structures. The optimal stemming length depends on factors such as the borehole diameter, explosive type, rock properties, and desired fragmentation. Generally, longer stemming lengths are preferred to maximize energy confinement and minimize airblast. However, excessively long stemming can reduce the effective explosive column length, potentially leading to poor fragmentation in the lower part of the borehole. Therefore, the stemming length must be carefully calculated and implemented to achieve optimal blast performance.

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What is the primary mechanism by which stemming length affects blast fragmentation and airblast overpressure?

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