## 2 Materials and Methods
### Experimental System  
The experimental system in this study consists of a universal testing machine and an AE monitoring system. The tests were performed on a Baldwin-Instron universal testing machine (capacity 900 kN), produced in Darmstadt, Germany, which is connected to a computer for data logging. The AE monitoring system is produced by the Lunitek S.r.l. Company of Sarzana in Italy. The system is equipped with eight piezoelectric sensors model LT18-003-PRD-00-R0 working in a frequency range of 15-625 kHz. These sensors were attached to each specimen using plasticine to prevent them from detaching during the loading process, and they were secured with rubber bands around the periphery, as shown in Figure 1. Figure 1a depicts the uniaxial loading system and AE system used in this study, while Figure 1b shows the Prismatic sample, granite. Figure 1c illustrates the cylindrical sample, basalt-rock. The AE sensor is bonded to the specimen and secured with rubber bands. The data acquisition system used a 5 MHz sampling frequency and stored data in parametric form. The AE waveforms generated during rock failure contain valuable information, such as AE ring-down counts, AE energy, AE amplitude, and duration, which can describe the rock's failure process. These parameters are illustrated in Figure 2.  
The recorded parameters for each detected signal were as follows [26]:  
Signal start time: the moment of the first reading that exceeded the detection threshold of 49 dB (280 \(\mu\)V).  
Peak amplitude: the maximum amplitude expressed in dB.  
Number of oscillations (counts): the number of intermediate crossings of the threshold by the signal.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Specimens** & \begin{tabular}{c} **Diameter** \\ **(mm)** \\ \end{tabular} & \begin{tabular}{c} **Length** \\ **(mm)** \\ \end{tabular} & \begin{tabular}{c} **Velocity** \\ **(mm/s)** \\ \end{tabular} & \
\begin{tabular}{c} **Peak Stress** \\ **(MPa)** \\ \end{tabular} &
\begin{tabular}{c} **Elastic Modulus** \\ **(Gpa)** \\ \end{tabular} \\ \hline
0–1 & 42 & 110 & 0.001 & 134.4 & 17.05 \\
0–2 & 42 & 100 & 0.01 & 179.3 & 13.7 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Cylindrical sample, basalt-rock parameters.  
Figure 1: Experimental equipment. Loading system (**a**), granite (**b**), basalt-rock k (**c**).  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Specimens** & \begin{tabular}{c} **Dimension** \\ **(mm)** \\ \end{tabular} & \begin{tabular}{c} **Velocity (mm/s)** \\ \end{tabular} & \
\begin{tabular}{c} **Peak Stress** \\ **(MPa)** \\ \end{tabular} &
\begin{tabular}{c} **Elastic Modulus** \\ **(Gpa)** \\ \end{tabular} \\ \hline
1–1 & 55 \(\times\) 55 \(\times\) 100 & 0.0025 & 144.20 & 5.16 \\
1–2 & 55 \(\times\) 55 \(\times\) 100 & 0.0025 & 212.41 & 6.44 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Prismatic Sample, granite Parameters.  
AE energy (\(E_{AE}\)): integral of the waveform. When the acquisition of the signal is parametric, it can be approximated by the envelope area of the triangle formed by the signal peak amplitude and its duration. The calculation of energy is described as Equation (1):  
\[E_{AE}=\sum_{i=1}^{N}\frac{A_{i}\times\Delta t_{i}}{2} \tag{1}\]  
where \(A_{i}\) is the amplitude of signal \(i\), mV.