# Effect of the Inter-Ring Delay Time on Rock Fragmentation: Field Tests at the Underground Mine
###### Abstract  
The effect of inter-ring delay time (IRDT) on rock fragmentation in the tunnel excavation blasting was studied at the Xinjang Beizhan Iron Mine, China, to improve the rock fragmentation and optimize the blast design. Blasting tests were conducted with an IRDT of 50, 100, 150, 200, and 500 ms; each adjacent ring had an equal IRDT, and two replicate tests were conducted. The blasting plan with IRDT of 100 ms was the original blasting plan used in the mine. Two optimized blasting plans were proposed and implemented based on the experimental results, along with a control experiment using the original blasting plan. The fragment size of each blast test was measured and analyzed by the block-analyzed software. Both collision theoretical and field tests indicated that the IRDT plays an important role in rock fragmentation and that as the IRDT increases, the degree of rock fragmentation increases first and then decreases. For example, the fragment sizes X20, X50, and X80 showed an increase followed by a decrease; the percentage of large fragments (1-P750) showed a decline followed by a rise; the percentage of small fragments P25 showed an increase followed by a decline. The blasting plan with an IRDT of 150 ms had the most optimal rock fragmentation effect, with the lowest percentage of large fragments, the highest percentage of small fragments, and the smallest average fragment size of X50. Furthermore, the two optimized blasting plans demonstrated better control over blasting costs and rock fragmentation compared to the original blasting plan. inter-ring delay time; rock fragmentation; tunnel excavation blasting; collision theory; field test +
Footnote †: journal: Medical  
indicates that delay time can affect the distribution and efficiency of explosive energy, thus controlling rock fragmentation [5]. In the analysis of the degree of crushing of underground mined ores, the following computer programs and methods are currently in common use: numerical simulation software like FLAC3D 7.0, UDEC 7.0, 3 DEC 7.0, etc. Numerical simulation can assist us in predicting and evaluating the impact of blasting on the quality of ore. By accurately simulating the propagation of blast waves within the ore body, it is possible to estimate the degree of ore fragmentation and distribution caused by blasting, thereby forecasting the dilution of the ore. Furthermore, numerical simulation can also assess the impact of blasting on the stability of the surrounding rock, thereby reducing losses and enhancing the efficiency and safety of mining operations. It can simulate the crushing process of underground mining ores and to simulate the mechanical behavior and damage patterns of rocks; image analysis techniques like Unet, RestNet, and other deep learning algorithms to semantically segment the ore, and then identify and measure the lumpiness of the ore; WipFrag SOLO lumpiness real-time monitoring and analysis system to monitor ore lumpiness quickly, accurately, and in real-time, and analyze it based on historical data to optimize the milling process; software CASRock, developed by Wuhan Institute of Geotechnics, Chinese Academy of Sciences, is used to analyze the fracture process of engineered rock bodies, simulating fine-scale fracture mechanisms and macroscopic equivalent mechanical responses. In terms of rock fragmentation, it is commonly believed that delay time affects the distribution and efficiency of explosive energy through stress waves, free surfaces, and collisions. Regarding stress waves, [PERSON] and [PERSON] used stress wave theory to describe how positive effects of stress wave interaction between two blast holes can be achieved with short delay times, improving rock fragmentation [6; 7]. [PERSON] and [PERSON] pointed out that the optimal delay time should cause longitudinal wave particle velocities to increase, and the results of the field tests showed an increase in the average fragment size of nearly 50% [8].