There is a lot of research on the impact of stemming contrivances and various stemming materials on fragmentation, but not as much on the influence of stemming length. The length of stemming that is required is somewhat dependent on the type of material used (Oates & Spiteri, 2021).
The more efficient a stemming material at containing explosive energy, the shorter the stemming length required (Oates & Spiteri, 2021). (Konya & Konya, 2018) state “the use of a proper stemming material can reduce the total amount of stemming needed by over 40%”.
A reduction in stemming length while maintaining the same confining effect allows additional explosives to be used in the hole and significantly improves the fragmentation in the collar (Konya & Konya, 2018).
Drill chippings, crushed aggregate, and stemming contrivances are the three categories of stemming material that are frequently addressed in stemming literature that deals with fragmentation. Since drill chippings are readily available throughout the charging process, they are frequently employed as the benchmark material.
Significant improvements in fragmentation have been observed when crushed aggregate is used to replace drill chippings. Authors generally agree that the use of crushed aggregate in the place of drill chippings results in improved fragmentation (Oates & Spiteri, 2021).
(Sharma & Rai, 2015) found that holes stemmed with drill chippings had K50 values higher than those stemmed with crushed aggregate. Where crushed aggregate was used in the place of drill chippings a reduction in the size distribution from 0.58–0.77 m to 0.45– 0.59 m was achieved. Additionally, the holes stemmed with crushed aggregate had a 21.2% better muckpile throw, and the productivity of loading and hauling improved by 18%.
(Kojovic, 2005) measured the impact of changing from drill chippings to crushed aggregate stemming at Red Dog mine in Alaska. The blasts stemmed with crushed aggregate significantly improved the uniformity of the ROM (run of mine), with a 36% reduction in semi-autogenous grinding (SAG) mill feed variability. When the ROM feed to the crushers is more uniform the settings on the crushers can be adjusted to reduce the energy required. With a 3% increase in the F80 size, a 5% reduction in the power input for the mill was recorded.
Additionally, the improved fragmentation as a result of the use of crushed aggregate reduced the wear on the crusher, resulting in a 20% longer period between crusher relines (Kojovic, 2005).
Reference
Kojovic, T. (2005). Influence of aggregate stemming in blasting on the SAG mill performance. Minerals Engineering, 18(15), 1398–1404. https://doi.org/10.1016/j.mineng.2005.02.012
Konya, C. J., & Konya, A. (2018). Effect of Hole Stemming Practices on Energy Efficiency of Comminution (K. Awuah-Offei, Ed.; pp. 31–53). Springer International Publishing. https://doi.org/10.1007/978-3-319-54199-0_3
Oates, T. E., & Spiteri, W. (2021). Stemming and best practice in the mining industry: A literature review. Journal of the Southern African Institute of Mining and Metallurgy, 121(8), 415–425. https://doi.org/10.17159/2411-9717/1606/2021
Sharma, S. K., & Rai, P. (2015). Investigation of Crushed Aggregate as Stemming Material in Bench Blasting: A Case Study. Geotechnical and Geological Engineering, 33(6), 1449–1463. https://doi.org/10.1007/s10706-015-9911-7
