# Analysis of Blasting Efficiency Using Crack-Inducing Holes and Pre-Splitting Method in Blasting
## 3 Experimental Results and Analysis
### Analysis of Pre-Crack Effect  
To analyze the vibration characteristics at each measurement location, a time-lag analysis was conducted. Time-lag analysis is a method used to observe the magnitude of vibrations occurring at different times of detonation, making it useful for comparing and analyzing vibration levels across different regions of the tunnel. The results of the time-lag analysis for each blasting cycle and measurement point are shown in Figure 8.  
Analyzing the vibration levels in the cut area, the maximum vibration speed during general blasting was 0.894 cm/s, while, during combined blasting, it was 0.595 cm/s, showing a 33.4% reduction in vibration. Similarly, in the expansion, periphery, and floor sections, the vibration levels reduced from 1.260 cm/s to 0.697 cm/s, resulting in a 44.6% reduction in vibration. This reduction is believed to be due to the formation of cracks between the pre-splitting holes and voids, which blocked the blasting vibrations from propagating to the periphery, thus reducing vibrations. However, during combined blasting, the vibrations at the periphery were larger than those in the cut, expansion, and floor sections. This is thought to be due to the energy from pre-splitting blasting not forming complete cracks, with some of the energy being converted into elastic waves that contribute to the blasting vibrations [26; 27; 28; 29]. The factors influencing blast vibration propagation can be classified into geological conditions and blasting conditions, as summarized in Table 4[30; 31; 32; 33]. Blast vibration is most strongly correlated with the amount of explosives used and the distance to the measurement point. Additionally, geological conditions also have a significant impact. These geological conditions are unchangeable parameters [16; 34], and factors such as joint spacing, orientation, and fracture zones significantly influence blast vibration propagation [35; 36]. Figure 7: Comparison graph. (a) Measurement point NO.1; (b) measurement point NO.2. \begin{table}
\begin{tabular}{c c c c c c} \hline \multirow{3}{*}{**Sequence**} & \multirow{3}{*}{**Blasting Method**} & \multicolumn{3}{c}{**Vibration Levels at Each Measurement Point (cm/s)**} \\ \cline{3-5}  & & \multicolumn{2}{c}{**NO.1**} & \multicolumn{2}{c}{**NO.2**} \\ \cline{3-5}  & & **PPV** & **Max PPV** & **PPV** & **Max PPV** \\ \hline
1 st & General & 0.468 & 0.805 & 1.260 & 1.260 \\ \hline
2 nd & blasting & 0.805 & 0.892 & 1.260 \\ \hline
3 rd & Combined & 0.495 & 0.838 & 1.260 \\ \hline
4 th & blasting & 0.730 & 0.730 & 0.838 \\ \hline \end{tabular}
\end{table} 
Table 3: Blasting vibration measurement data. To minimize blast vibration, it is necessary to adjust the blasting conditions, which are variable parameters. The most influential factors include the type of explosive, charge per delay, and delay time of detonation. Additionally, drilling angle, burden, and hole spacing also affect vibration levels. When conducting pre-splitting blasting to minimize vibration, the type of explosive and burden and hole spacing are considered the most critical factors. Low-vibration explosives exhibit a detonation velocity of approximately 60% of that of emulsion explosives,