# Effect of the Inter-Ring Delay Time on Rock Fragmentation: Field Tests at the Underground Mine
## 6 Discussion  
In the case of using explosives to mine deposits, the degree of rock fragmentation is the standard for judging the blasting effect. Therefore, the degree of rock fragmentation is extremely important. For tunnel excavation blasting, due to the confinement effect of rock caused by only one free face, the cut blasting technique is usually used to increase the free surface and compensation space to improve rock fragmentation. Based on Section 3.4, the free face formed by the cut holes was divided into partial free surfaces and new free surfaces. In this regard, the effect of IRDT on the free surface and compensation space was analyzed by the blasting process. Then, the effect of IRDT on rock fragmentation was analyzed through collision theory. The obstructed completely free surfaces (i.e., the new free surface of this article) are more conducive to rock fragmentation than the partial free surfaces [25], based on the blasting process in Section 3.3; this can explain that changes in IRDT will also affect rock fragmentation. However, it is difficult to explain the case where IRDT is large. As shown in Figure 6c, although the R2 detonation forms a muck pile in the blasting cavity, the new free surfaces are still obstructed completely for R3, which is also conducive to rock fragmentation. This is different from the conclusion drawn in this article considering the collision of rocks in the same inter-ring, which is because the effect of inter-ring rock collision may be higher than the effect of obstructed completely free surfaces, or the motion of the obstruction has not been considered for the effect of obstructed completely free surfaces on rock fragmentation, which requires further research in subsequent experiments.  
According to the consideration of same-ring rock collision in this article or the conclusion proposed by [PERSON] [25], to achieve sufficient rock fragmentation, a longer IRDT can be set to provide more collision space and a completely free face for the later blasting. As mentioned in Section 3.4, this will cause the later blasting rock to accumulate in the blasting cavity, reducing the collision space for subsequent blasting. At this time, appropriately reducing the minimum resistance line of the later blast hole can enable the rock thrown after the collision to be completely thrown, increasing the collision space for subsequent blasting and improving rock fragmentation. Therefore, the IRDT needs to be further discussed based on the tunnel width and the inclination angle of the blast holes.  
As mentioned above, the IRDT affects the distribution of explosive energy, and further exploration is needed on its specific effects. The energy generated by the explosive can be converted into rock fragmentation, throwing, vibration, and other energy. In this blasting test, for the energy used to break rocks, the increase in inter-delay time shows a trend of first increasing and then decreasing. It is still unknown how IRDT affects the conversion of other energies. Therefore, future investigations can focus on the effects of IRDT on vibration and rock displacement and how it affects the distribution of explosive energy.