## 2 Methodology
### Experimental Drilling and Sensing Methodology  
This section describes the properties of the disintegrated rocks, the methods of conducting experimental drilling, and the recording of the vibration signal.  
The primary objective of rotary diamond core drilling is to obtain a drill core in the shape of a cylinder, the compactness of which is determined by the rock's drill ability and physical mechanical properties. The quality of the work is evaluated by the core yield, which is the ratio of the drilled length of the well to the length of the obtained core.  
When drilling, the primary parameter is the number of revolutions (speed) and compressive (pressure) force of the diamond drilling tool. For experimental works, the selected revolutions are \(n=1000\) rpm and the compressive force \(F=5000\) N. The drilling used a 6-channel drilling tool. The drilled rocks were andesite, granite, limestone, and artificial rock concrete.  
The drilled rocks were selected based on their availability from the surrounding quarries. The rock samples selected (Table 1) are very fine-grained (limestone), fine-grained rock (andesite), and medium- to coarse-grained rock (granite). Concrete was selected as a soft, artificial rock with a coarse-grained material. Andesite and granite are igneous rocks, and limestone is a sedimentary rock.  
Selected properties of the tested rocks are below [27; 33; 34] (Table 1):  
* Andesite is an igneous rock that is grey to dark grey with frequent porphyritic growths of minerals. It contains essential minerals such as plagioclase, amphiboles, pyroxenes, biotite, and quartz. Andesite can also contain secondary minerals such as opal from cavities in basalts.
* Granite is a hard igneous rock that can be white, pink, grey, or orange, depending on the mineral composition. It contains essential minerals, mainly feldspar quartz, and secondary minerals in smaller quantities, such as biotite, muscovite, amphibole, and others.
* Limestone is a sedimentary rock that is typically white, grey, or tan. It contains mainly essential minerals such as calcite carbonate, usually in the form of calcite or aragonite.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Rock Name** & **Rock Sample** &
\begin{tabular}{c} **Compressive** \\ **Strength (MPa)** \\ \end{tabular} & **Density (g/cm\({}^{3}\))** & **Grain Size** \\ \hline Andesite—a & & Very strong & 100–250 & 2.5–2.8 & Very fine-grained \\ \hline Granite—g & & Extremely strong & 2.5–2.8 & Medium- to coarse-grained \\ \hline Limestone—l & & Very strong & 2.5–2.8 & Fine-grained \\ \hline Concrete—c & & Medium strong & 25–50 & 2.2–2.4 & Coarse-grained \\ \hline \hline \end{tabular}
\end{table}
Table 1: The properties of the tested rock [27; 33; 34].  
It may also contain magnesium carbonate (dolomite) and minor components such as clay, iron carbonate, feldspar, pyrite, and quartz.
* Concrete is a solid building material consisting of aggregate (gravel and sand) and binder (water and cement). It has the properties of natural stone. The nearest natural rock to concrete is sandy limestone. The typical concrete mix comprises roughly 10% cement, 20% air and water, 30% sand, and 40% gravel.  
The drilling experiments were conducted by securing a sample of the chosen rock into a mechanical fixture on the drilling stand. The appropriate drilling mode was then selected, and the ADASH 3900-II measurement system recorded the vibration signal produced during the rock drilling. The vibration acceleration signal was measured for 20 seconds with a sampling frequency of 18 kHz and a sampling period of 0.55 ms, which covers a frequency range from 0 to 9 kHz. These vibration signal characteristics are consistent across all drilled rocks. Since the vibration signal is stationary for management purposes, it can be represented by \([x_{i}]^{n}{}_{i-1}\), where \(n=16\),384 is the number of samples in the signal.