# Effect of the Inter-Ring Delay Time on Rock Fragmentation: Field Tests at the Underground Mine
## 2 Mine Condition  
The Beizhan Iron Mine is an underground iron mine located 160 km away in the 327\({}^{\circ}\) direction from Xinjiang's Hejing County. The deposit is located at the eastern end of the Aulal metallogenic belt on the Tarim Plate. The lithology of the ore rocks is dominated by chloroidized silica, magnetized silica, and crystalline tuff, with their rock mechanics parameters shown in Table 1. The metal minerals of the ore are magnetite, followed by pyrite and magnetic pyrite, with small amounts of spalexite and chalcopyrite. According to the statistical results of the RQD values of drill holes, most rocks in the mine area have poor to medium integrity, and the rock quality grade is III to IV.  
The original blasting pattern is shown in Figure 2. The test tunnel section size was 4.2 m \(\times\) 4.0 m, and we adopted double wedge cut-smooth blasting. Drilling was performed using a YT-27 hand-held rock drill. Fifty blast holes with a diameter of 44 mm were arranged in the tunnel section, the angle (\(\theta\)) between the blast holes and the free surface on the lower section gradually increasing from the section centerline along the horizontal direction to the contours. The diagram illustrates holes of varying colors, each corresponding to a different charge of explosives, a design consideration that takes into account the intended purposes and expected effects of the blast. Owing to the distribution of energy necessary for rock fragmentation in blasting, the different types of holes--pilot holes, auxiliary holes, peripheral holes, and side holes--play specific roles. Pilot holes are used to commence the rock-breaking process, auxiliary holes assist in enlarging the area of fragmentation, and peripheral and side holes are employed to control the blast pattern and the dispersion of the broken rock material. No. 2 rock emulsion explosives were used for blasting, with a single  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Ruggedness** & \begin{tabular}{c} **Wave Speed** \\ **(km/s)** \\ \end{tabular} & \begin{tabular}{c} **Tensile Strength** \\ **(MPa)** \\ \end{tabular} & \begin{tabular}{c} **UCS** \\ **(MPa)** \\ \end{tabular} & \
\begin{tabular}{c} **Young’s Modulus** \\ **(GPa)** \\ \end{tabular} &
\begin{tabular}{c} **Poisson’s Ratio** \\ \end{tabular} \\ \hline Chloritized silica & 3.24 & 7.7 & 56.4 & 38 & 0.20 \\ Magnetized silica & 4.11 & 10.2 & 82.1 & 44 & 0.27 \\ Crystalline tuff & 3.53 & 8.3 & 59.3 & 35 & 0.20 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Physical and Mechanical Parameters of ore rocks.  
Figure 1: The schematic diagram of blasting rock-breaking.  
blasting consumption of 220 rolls and a total of 66 kg. The blasting sequence followed the legend from top to bottom. Two types of detonators, digital electronic detonators and shock tube detonators produced by Xuefeng Company, were used in the mine; each blasting required 50 detonators. For the digital electronic detonators blasting plan, the IRDT of each adjacent ring is equal and the delay time is 100 ms. Due to the high precision and controllable delay of the digital electronic detonators, which can reduce the errors caused by delay time, they were selected for the experiment to investigate the effect of different IRDTs on rock fragmentation.