The goal of having the best rock fragmentation is paramount in order to achieve economic efficiency in mining and civil engineering activities. The optimization of the spacing of drill patterns plays an integral role in achieving this objective by managing the two main sources of cost in mining operations – overbreak and secondary breakage. Spacing of the drill patterns is characterized by the geometry of the holes that form the pattern in terms of the burden (distance to the nearest free face) and spacing (distance between neighboring holes). Overbreak refers to the breakage of rocks beyond the intended area as a result of explosives.
The main objective of blasting design is to ensure that the energy is distributed effectively in the rock body. The shock wave interaction is determined by the relation between the burden and spacing. As the spacing is optimized, the energy generated causes an even fracture of the rock. Changes in effective burden and spacing affect the confinement and rigidity of the explosive, hence impacting the fragmentation as well as in-flight collision of the fragmented rock in the process of blasting (Chouhan et al., 2022). Proper calibration of the geometric configuration helps to ensure that the energy is not wasted into the air or concentrated within the host rock.
There exists an issue of secondary breakage, which poses a significant challenge on productivity due to need for rock fracturing through mechanical means or secondary blasting. This issue usually arises from use of large drill spacings, thereby creating complete rock blocks between holes. In order to control fragment size, the blast engineer should vary the spacing based on the geological characteristics of the site. Rock joint densities and orientations determine primary block sizes, hence requiring varied spacing based on the configuration to avoid large fragments (Lapčević et al., 2023).
Loose boulders are formed when there is too much space between holes, while overbreak will happen if the space between holes is very little. In the case where blastholes are close together, the overlapping shock waves will be highly damaging to the surrounding rock. It should be noted that the amount of damage that will occur depends heavily on the geological properties of the rock. In particular, the presence of natural discontinuities in the rock will change how damage occurs around blasting. It will be more concentrated around the weak zones in the rock.
In the past, engineers relied heavily on simple empirical equations to predict ideal spacing. Currently, in the optimization of parameters for blasting design, the use of sophisticated data-driven approaches is applied. The application of machine learning models makes it possible to predict accurately the effects of blasts by continuous monitoring of factors including the state of the ground, powder factor, and shape of the drilling pattern (Dumakor-Dupey et al., 2021). This ensures that the energy released by blasts is channeled to produce effective fragmentation.
In summary, the optimal spacing of drill patterns is one of the basic economic requirements in rock excavation. The ability to attain the right balance between the burden and spacing allows for the prevention of both the dangers of overbreaks and oversized boulders. The use of customized blasting designs supported by geostatic analysis and prediction models guarantees fragmentation uniformity. In the end, this optimal design results in lower costs associated with secondary fragmentation and wall repairs.
References
Chouhan, L. S., Raina, A. K., Murthy, V. M. S. R., Sabri Sabri, M. M., Mohamad, E. T., & Bhatawdekar, R. M. (2022). Advanced analysis of collision-induced blast fragmentation in v-type firing pattern. Sustainability, 14(23), 15703. https://doi.org/10.3390/su142315703
Dumakor-Dupey, N. K., Arya, S., & Jha, A. (2021). Advances in blast-induced impact prediction—A review of machine learning applications. Minerals, 11(6), 601. https://doi.org/10.3390/min11060601
Lapčević, V., Torbica, S., Stojanović, M., & Vojinović, I. (2023). Development and validation of universal 3D blast fragmentation model. Applied Sciences, 13(14), 8316. https://doi.org/10.3390/app13148316
Pan, R., Wang, P., Zhou, Z., Lan, R., Chen, L., Yang, H., Chen, C., Zhang, J., & Liu, Y. (2023). Effects of confining stress on blast-induced damage distribution of rock with discontinuity. Sustainability, 15(17), 13278. https://doi.org/10.3390/su151713278
