## 3 Results
### Fragment Size Distribution
Figure 16 shows the fitted curves for BS4-BS6 with inter-hole delays in the range of 150-250 us. In 1-80% mass passing, the fitted curves for the three specimens move upward in log-log space. The movement trend of the fitted curves shows that rock fragmentation improved with the increased inter-hole delay (from 150 to 250 us). As seen in Figure 16, the fitted curve of BS4 was close to that of BS5, i.e., the difference between the particle sizes at the same mass passing was insignificant. For example, particle size at 10% mass \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Bench** & **Inter-Hole** & \(x_{1}\) & \(x_{10}\) & \(x_{50}\) & \(x_{100}\) \\
**Specimen** & **Delay** & **(\(\mu\)s)** & **(mm)** & **(mm)** & **(mm)** \\ \hline BS1 & 0 & 1.06 & 28.08 & 122.1 & 195.4 \\ BS2 & 50 & 1.14 & 31.72 & 121.3 & 166.3 \\ BS3 & 100 & 1.99 & 43.18 & 128.4 & 237.1 \\ BS4 & 150 & 0.92 & 33.12 & 112.7 & 167.4 \\ BS5 & 200 & 0.89 & 27.69 & 103.7 & 171.5 \\ BS6 & 250 & 0.46 & 17.05 & 65.9 & 105.7 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: The particle sizes at the given four mass passings. Figure 15: Fitted curves of BS1–BS3. passing was 33.1 mm and 27.7 mm for BS4 and BS5, respectively, with a difference of 5.4 mm. The particle size of BS6, with an inter-hole delay of 250 us, was significantly smaller than that of BS4 and BS5 in the mass passing of 1-100%, indicating that fragmentation was significantly improved at this delay time. Compared to BS5, BS6 had decreased values for \(x_{50}\) (by about 36.5%) and \(x_{100}\) (by about 38.4%). In summary, BS6 produced the most uniform rock fragmentation. Using \(x_{50}\) as the indicator for evaluating the effect of blast fragmentation in this study, Figure 17 shows the histograms of median size versus delay time. As shown in Figure 17, BS6 obtained the best fragmentation, while BS3 achieved the worst fragmentation. In addition, Figure 7 shows that in the range of 0-100 us, the increase in delay time did not effectively improve fragmentation, shown by BS3 obtaining the maximum \(x_{50}\) value. In the inter-hole delay of 100-250 us, \(x_{50}\) gradually decreased as delay time increased. When the inter-hole delay reached 250 us, the median size of BS6 decreased by approximately 48.7% compared to that of BS3, which means that fragmentation was significantly improved. Figure 18 shows the connected scatterplots of the median sizes and blast excavation weights of all specimens. The black line of the connected scatterplots represents the variation in median size, the red line of the connected scatterplots represents the variation  
Figure 16: Fitted curves of BS4–BS6. Figure 17: Median size of each bench specimen. in blast excavation weight, and the blue dashed square represents the location of the best blast excavation quality. As shown in Figure 18, although BS6 produced the smallest median size, it also obtained the minimum blast excavation weight of 47.2 kg. BS3, with the maximum blast excavation weight of 85.2 kg, produced the largest median size, and the particle size in the coarse zone was significantly larger than that of the other experiments. In the remaining four blasting experiments, BS5 obtained the smallest median size and the maximum blast excavation weight of 65.9 kg. Considering the blast excavation weights and the obtained fragmentation distribution results of all bench specimens, BS5 recorded the best blast excavation quality, with the optimum delay time being 200 \(\upmu\)s.