Introduction
Blasting is a crucial operation in the mining and construction industries, used to fragment rock masses to facilitate their excavation and processing (Taiwo et al., 2023). The effectiveness of blasting is heavily influenced by various parameters, among which stemming length plays a critical role. Stemming, the inert material used to fill the blast hole above the explosive charge, impacts the efficiency of the blast and the resulting fragmentation. This was the first part of this article explores the effect of stemming length on blasting fragmentation, examining how variations in stemming length can influence rock fragmentation and overall blast performance.
The Role of Stemming in Blasting
Stemming serves multiple functions in blasting:
1. Containment of Explosive Energy: By confining the explosive charge within the blast hole, stemming helps to direct the energy of the blast towards the rock mass, enhancing fragmentation.
2. Control of Blast Dynamics: Proper stemming helps to control the direction and magnitude of the blast, reducing the risk of flyrock and controlling the fragmentation process.
Effect of Stemming Length on Fragmentation
1. Fragmentation Size and Distribution:
a. Short Stemming Length: When stemming length is insufficient, the explosive energy is not effectively contained within the blast hole. This results in poor fragmentation and larger boulders due to the uncontrolled release of energy. Short stemming can also lead to increased flyrock and ground vibration, which can affect the safety and efficiency of the blasting operation.
b. Optimal Stemming Length: An optimal stemming length ensures that the explosive energy is adequately contained, resulting in more controlled fragmentation. The energy is directed towards the rock mass, leading to a more consistent particle size distribution and reducing the occurrence of oversized fragments.
c. Long Stemming Length: Excessively long stemming can also be detrimental. While it might contain more energy, it can also lead to inefficient energy transfer, as the additional stemming material absorbs some of the energy, reducing the effectiveness of the blast. This can result in suboptimal fragmentation and increased risk of blocky or oversize fragments.
Langefors and Kihlstrom (1963) conducted pioneering work in blasting techniques and highlighted the importance of stemming length in achieving desired fragmentation. Their research demonstrated that improper stemming could lead to significant variations in fragmentation size and distribution.
Image analysis software like WipFrag enhances blast assessment by providing precise fragmentation analysis, helping to optimize stemming length for improved fragmentation control, reduced oversized fragments, and enhanced overall blasting efficiency (See attached images below). The attached images show relationship between stemming and Fragmentation size.
