# Effect of the Inter-Ring Delay Time on Rock Fragmentation: Field Tests at the Underground Mine
## 5 Results  
The description of the experimental rock fragmentation results was obtained by image analysis of Split-Desktop 4.0 and Swebrec function analysis. The authors proved that the Swebrec function fitted well with the screened cumulative distribution curve [22]. The Swebrec function proposed by [PERSON] is [24]:  
\[P(x)=\frac{1}{1+\left[\frac{ln\frac{x_{max}}{mx}}{ln\frac{x_{max}}{x_{50}}} \right]^{b}} \tag{5}\]  
where \(x_{50}\) is the average fragment size, \(x_{max}\) is the maximum fragment size, and \(b\) is the curve unodulation parameter. The Swebrec function has a useful prediction range in \(X_{P}\), where \(2\%<P<100\%\).  
In this study, a total of 18 blast tests were conducted. The corresponding fragment size datasets for each test were obtained using the Split-Desktop 4.0. The Swebrec function was then used to fit each dataset, and the function parameters \(b\), coefficient of determination R2 of each fit, are shown in Table 3. The results of rock fragmentation after blasting are presented in Tables 4 and 5 and Figures 13-16.  
The image processing data were compared with those fitted by the Swebrec function. The coefficient of determination R2 ranged from 0.99243 to 0.99931, indicating a good fit, as shown in Table 3.  
The blasting tests in test areas 1-3 all exhibited a significant effect of IRDT on rock fragmentation. With the increased IRDT, the percentage of small fragments P25 showed a trend of increasing and then decreasing; the percentage of large fragments (1-P750) showed a trend of decreasing and then increasing. Meanwhile, the percentage of fragment sizes X20, X50, X80, and Xmax all showed a trend of decreasing and then growing with the IRDT, as shown in Tables 3 and 4 and Figures 13-15. The test results were consistent with the IRDT on rock fragmentation mentioned in Section 3.4; the IRDT increased or decreased to a particular value, and the rock fragmentation impact was weakened. The blasting tests in test areas 1-3 also showed that the blasting with an IRDT of 150 ms provided the maximal number of small-sized fragments, the minimal number of large-sized ones, and the smallest average fragment size, indicating that the blasting solution with an IRDT of 150 ms provided more effective rock fragmentation than all other plans.  
\begin{table}
\begin{tabular}{l c c c c c c c c c c} \hline \hline Test field 1, & & & & & & & &  
The results of the three blasting tests in test area 4 are shown in Tables 3 and 5 and Figure 16. Compared with the control test (original blasting plan), Optimization Plan 1 (blast with an IRDT of 150 ms) reduces the fragment sizes X20, X50, X80, and the percentage of large fragments (1-P750) by 37.37%, 21.21%, 13.45%, and 90.37%, respectively, while increasing the percentage of small fragments P25 by 21.63%. This indicates that the rock fragmentation degree of Optimization Plan 1 is better than that of the original blasting  
Figure 14: Accumulated mass passing (%) versus fragment size in the test field 2. (**a**) In a linear scale; (**b**) in a logarithm scale.  
Figure 13: Accumulated mass passing (%) versus fragment size in the test field 1. (**a**) In a linear scale; (**b**) in a logarithm scale.  
design, which is consistent with the results of the IRDT blasting test. Moreover, this also suggests that, without changing the cost, rock fragmentation can be improved by controlling the IRDT. Compared Optimization Plan 2 (the reduced-hole blast with an IRDT of 150 ms) with the control experiment, the fragment sizes X20, X50, and X80 increased by 49.64%, 12.51%, and 2.05%, respectively, and the percentage of small fragments P25 decreases by 20.31%, but the percentage of large fragments (1-P750) decreases by 25.19%.  
Figure 16: Accumulated mass passing (%) versus fragment size in the test field 4. (**a**) In a linear scale; (**b**) in a logarithm scale.  
Figure 15: Accumulated mass passing (%) versus fragment size in the test field 3. (**a**) In a linear scale; (**b**) in a logarithm scale.