## 3 Loose Ring Measurement
### Sonic Method for Testing Loose Rings  
Due to rock fragmentation within the loosening ring, ultrasound propagates through the fractured rock at a lower velocity compared to intact rock. The extent of the loosening circle can be determined by identifying the inflection point on the velocity curve, where a sudden change in sound speed occurs. By screening, analyzing, and processing the data collected from the measurement points at the Makeng Iron Mine, a depth-sound velocity variation curve for the lithology at each measurement point was obtained, as shown in Table 3 and Figure 3.  
In the 85 m, 115 m, and 145 m subsections, the relationship between ore body hole depth and acoustic wave velocity was analyzed. As shown in Figure 3, the measurement section at the 85 m level ranges from 0.8 m to 4.0 m. Within the 1.5 m to 4.0 m range, the rock wave velocity remains relatively stable between 3800 m/s and 4300 m/s, indicating that this section of the ore body is relatively intact. It has not been significantly affected by the stress changes induced by roadway excavation.  
However, between 1.2 m and 1.8 m, the wave velocity shows a noticeable decline. Specifically, within the 0.8 m to 1.4 m range, the average wave velocity is approximately 2112 m/s, which is significantly lower than the intact rock. This suggests that the rock mass in this section contains more fissures and is more fragmented due to the influence of roadway excavation. Based on this analysis, the loosening circle radius for the 85 m section is determined to be 1.2 m.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \begin{tabular}{c} **Hole** \\ **Number** \\ \end{tabular} & **Position** & **Rockiness** & \begin{tabular}{c} **Depth of** \\ **Hole (m)** \\ \end{tabular} & \begin{tabular}{c} **Effective** \\ **Hole** \\ **Distance (m)** \\ \end{tabular} & \
\begin{tabular}{c} **Average** \\ **Speed of** \\ **Sound (m/s)** \\ \end{tabular} &
\begin{tabular}{c} **Rock Average** \\ **Sound Velocity** \\ **(m/s)** \\ \end{tabular} & **Note** \\ \hline \multirow{3}{*}{1} & 85 level 24\# & & & & & \\  & transverse drift & & & & & \\  & 115 level 28\# & & & & & \\  & transverse drift & & & & & \\  & 145 level 28\# & & & & & \\  & transverse drift & & & & & \\  & 1500 & & & & & \\  & & & & & & \\ \hline \hline \end{tabular}
\end{table}
Table 3: Locations of test holes and measured sound velocities for each ore body at Makeng Iron Ore Mine.  
Figure 3: Curve of hole depth versus sound velocity in the ore body.  
Similarly, in the 115 m subsection, as shown in Figure 3, the acoustic wave test data exhibit the same trend as the 85 m section. Based on these results, the loosening circle radius for the 115 m level is determined to be 1.4 m.  
For the 145 m level, the measured wave velocity remains relatively stable within the 0.8 m to 4.0 m range. However, an overall decreasing trend in wave velocity suggests that, while the rock mass in this section remains largely intact, it is still influenced by excavation activities near the roadway. Consequently, the loosening circle radius in this section is relatively small.  
The sonic test results across different roadway sections within the ore body rock layers exhibit a consistent distribution pattern, with multiple factors influencing the extent of the rock loosening circle. Based on sonic testing and data analysis, it is concluded that the loosening circle size in the 85 m section is approximately 1.2 m, while in the 115 m section, it is around 1.4 m. In the 145 m section, the ore body exhibits better integrity, with only a small loosening circle present. These findings provide valuable insights into roadway stability and serve as a basis for optimizing support measures.