# Effect of the Inter-Ring Delay Time on Rock Fragmentation: Field Tests at the Underground Mine
## 7 Conclusions  
Based on the analysis of energy conversion in inelastic collision, it can be concluded that the degree of object destruction during collision depends on the relative velocity in the horizontal direction. In the analysis of the effect of IRDT on rock fragmentation in tunnel excavation blasting, the collision factor between the same ring rock was taken into consideration. It was found that the appropriate choice of IRDT influenced the distribution of explosive energy and improved rock fragmentation. When the IRDT was too short or too long, the degree of rock fragmentation was reduced. To address this, the IRDT blasting tests were conducted. Based on the analysis of rock fragmentation energy and the results of IRDT blasting tests, two optimized blasting plans were proposed. Compared with the original blasting plan, both sets of optimized blasting plans achieved better control over blasting cost and rock fragmentation. 1. IRDT blasting tests
* For blasting tests with IRDTs of 50, 100, 150, 200, and 500 ms, the content of the percentage of small fragments P25 and the fragment sizes X20, X50, X80, andXmax first increased and then decreased, while the percentage of large fragments (1-P750) decreased first and then increased. * Among the test plans, the delay timing of 150 ms resulted in the lowest percentage of large fragments (1-P750) and the highest percentage of small fragments (P25 mm), indicating better rock fragmentation. * Optimized blasting tests
* Compared with the control test (original blasting plan), optimized plan 1 achieved better rock fragmentation without changing the blasting cost. For example, the fragment sizes X20, X50, and X80, and the percentage of large fragments (1-P750) reduced by 37.37%, 21.21%, 13.45%, and 90.37%, respectively, and the percentage of small fragments P25 increased by 21.63%. * Furthermore, optimized plan 2 achieved a cost reduction while maintaining the degree of rock fragmentation, with the use of digital electronic detonators and explosives reduced by 14.0% and 27.27%, respectively. Conceptualization, H.C. and C.L. ; methodology, H.C.; software, H.C. and C.L. ; validation, Y.F. and H.Y. ; formal analysis, H.C.; investigation, H.C., Y.F. and H.Y. ; resources, C.L. ; data curation, H.C.; writing--original draft preparation, H.C.; writing--review and editing, C.L. and Y.F. ; visualization, H.C.; supervision, H.C.; project administration, H.C.; funding acquisition, H.C. All authors have read and agreed to the published version of the manuscript. This research was funded by the Accurate Delay Rock Breaking Mechanism and Key Technology Innovation Team, grant number 2020D14043. The original contributions presented in the study are included in the article, further inquiries can be directed to the corresponding author. We are grateful to the anonymous reviewers for their insightful and constructive comments for improving the manuscript. [PERSON] was employed by the company North Blasting Technology Co., Ltd. (Beijing China). The remaining authors declare that the research was conducted without any commercial or financial relationships that could be construed as a potential conflict of interest. * [PERSON] and [PERSON] (2013) [PERSON]; [PERSON] Shock Wave Interactions in Rock Blasting: The Use of Short Delays to Improve Fragmentation in Model-Scale. _Rock Mech. Rock Eng._**2013**, _46_, 1-18. [CrossRef]
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* [PERSON] and [PERSON] (1993) [PERSON]; [PERSON] Calculation of Energy Distribution from Concentrated Explosive Charges in Rock. _Blasting Equip._**1993**, 1-5. [PERSON] Mechanics of Geological Materials. _Appl. Mech. Rev._**1985**, _38_, 1256.