## 3 Engineering Context and Site Condition
### Acoustic Testing  
The acoustic testing of rock masses is widely employed to detect geotechnical parameters, faults, weak interlayers, and loose zones. The principle behind this method is based on the propagation speed and attenuation coefficient of sound waves within the rock mass. By measuring these parameters, the properties of the rock mass can be inferred. In the mining field slope, ultrasonic testing using borehole techniques was utilized. Ultrasonic equipment was used to measure sound wave parameters along the vertical axis, allowing for the analysis of the engineering characteristics of the surrounding rock at various depths. As shown in Figure 5, this is a schematic diagram of the ultrasonic testing process. The  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Weak Structural** & **Occurrence** & **Thickness (cm)** & **Opening Width** & **Filling Material** \\ \hline L\({}_{1}\) & 160 \(\angle\) 24 & 35 & Large & Chlorite \\ L\({}_{2}\) & 282 \(\angle\) 46 & 11\(\sim\)20 & Large & Chlorite \\ \hline \hline \end{tabular}
\end{table}
Table 1: Statistics of each weak interlayer.  
Figure 4: Radar detection results at the transfer station. (**a**) Line 1 schematic diagram of geological radar test results; (**b**) Line 2 schematic diagram of geological radar test results; (**c**) Line 3 schematic diagram of geological radar test results.  
RSM-SY7 non-metallic ultrasonic system from Zhongyan Technology was employed, along with its principle diagram, where transmitters and receivers are placed within the rock mass. By transmitting and receiving acoustic pulse signals, characteristics such as changes in acoustic impedance, wave velocity, energy attenuation, frequency variations, and waveform distortions are analyzed to identify the type, size, and location of defects in the rock mass. An acoustic velocity-depth curve is constructed to assess the nature and extent of these defects.  
Acoustic Testing Results  
The ultrasonic testing results from the field are presented in Figure 6 for the three selected boreholes, as follows:  
Figure 6a--B1 Borehole: The measured wave speeds ranged primarily from 2247 m/s to 3846 m/s, with a minimum value of 1566 m/s and a maximum value of 3846 m/s.  
Figure 6b--B2 Borehole: The measured wave speeds ranged primarily from 2353 m/s to 3922 m/s, with a minimum value of 1266 m/s and a maximum value of 3922 m/s.  
Figure 6c--B3 Borehole: The measured wave speeds ranged primarily from 2439 m/s to 3774 m/s, with a minimum value of 1515 m/s and a maximum value of 4082 m/s.  
Based on these test results, it can be inferred that the loose zone in the surrounding rock of Borehole B1 is located approximately between 3.25 and 3.75 m, while the loose zone in Borehole B2 is found between 2.50 and 2.75 m. Additionally, the acoustic velocity data from the surrounding rock predominantly falls within the range of 2500 to 4000 m/s, indicating that the surrounding rock is affected by joint fissures. This results in a blocky and fractured structural characteristic of the rock mass.  
Figure 5: Schematic diagram of the single transmitter and dual receiver ultrasonic testing.  
Figure 6: Schematic diagram of ultrasonic testing. (**a**) B1 Borehole ultrasonic testing results; (**b**) B2 Borehole ultrasonic testing results; (**c**) B3 Borehole ultrasonic testing results.