# The Role of Delays in the Performance of Blasting
## 3 Results  
The results are summarized in charts reported in Figures 5-12. Each chart features a dashed line, not representing linear regression but serving as a visual indicator of the data trend on the scatterplot. The incidence of the use of a hydraulic secondary breaker, quantified by \(S_{b}\), serves as an indicator of the quality of fragmentation: the fewer hours that the hydraulic hammer operated per unit of volume of blasted rock, the better the fragmentation. Figure 5 shows the increase in hydraulic hammer usage with the increasing number of adjacent holes blasted with the same delay. The experimental data points reported in Figure 6 show that as the blasthole density increased with a D larger than 3 m (number of blastholes with D > 3 m, normalized with respect to the total number of blastholes tended toward 1), the value of \(S_{b}\) decreased considerably, with some experimental points approaching 0. On the contrary, Figure 7 shows that increasing the density of blastholes with D = 2 m resulted in an approximately proportional increase in the quantity of fines produced. In other words, increasing the distance between simultaneous holes led to a better distribution of explosive energy, resulting in more homogeneous fragmentation a lower fine content. Figure 5: The frequency of hydraulic secondary breaker usage as a function of the number of adjacent holes per delay. Figure 6: The frequency of a hydraulic secondary breaker usage as a function of the number of adjacent holes per delay. These combined results indicate the same behavior as discussed above: Managing a better decomposition of the blast by increasing the distance between simultaneous holes can induce the explosive to work along the burden toward the free surface, instead of through the spacing between holes. This leads to more homogeneous fragmentation, reducing the production of coarser material while also preventing an excess of fines. Figure 8 shows a decrease in the percentage of fines with an increase in delay density. Under the same conditions, an increase in SP dramatically decreased the particle size, quantified through P80 in the present study, as depicted in the trend shown in Figure 9.  
These combined results indicate the same behavior as discussed above: Managing a better decomposition of the blast by increasing the distance between simultaneous holes can induce the explosive to work along the burden toward the free surface instead of through the spacing between holes, obtaining a more homogeneous fragmentation that reduces the production of coarser material while also preventing an excess of fines. On the contrary, simultaneous holes at close distances can result in the cooperation of charges along the line connecting the two hole axes. This may induce the explosive energy to work along the surface between the holes with a shearing effect, instead of producing fragmentation. Figure 8: When more delays are used per unit of blasted rock, fewer fines result from the blast. Definition of “fines”: material passing a mesh of 5 mm. Figure 7: The impact of the number of blastholes with D = 2 m on the percentage of fines in the muckpile. Increasing the distance between simultaneous holes reduces the likelihood of creating a shearing effect, directing the explosive energy to work along the line of least energy (the burden) to promote fragmentation. Considering the downstream processes, as mentioned before, the frequency of hydraulic secondary breaker usage serves as an indicator of fragmentation quality. According to the experimental points in Figure 10, a higher SP resulted in reduced usage of a hydraulic hammer for secondary breaking. This observation aligns with the trend depicted in Figure 11: The higher the specific priming, the smaller the particle size, thus leading to lower electricity costs at the primary crusher.