## 4 Data Analysis and Results
### Development of BTS Classification  
The UCS classification suggested by the IAEG [87] was used as the base for the BTS classification of igneous stones. As shown in Table 5, rocks fall into five classes according to their UCS values, namely, weak (UCS < 15 MPa), moderately weak (UCS 15-50 MPa), strong (UCS 50-120 MPa), very strong (UCS 120-230 MPa), and extremely strong (UCS > 230 MPa). \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Reference** & **Rock Class** & **Correlation Equation** & **Correlation Type** & **r** \\ \hline Tugrul and Zarif [46] & Igneous & UCS \(=\)\((6.67\times\text{BTS})+0.73\) & Linear & 0.96 \\ [PERSON] et al. [58] & Various & UCS \(=\)\(10.61\times\text{BTS}\) & Linear & 0.73 \\ Altindag and [PERSON] [74] & Various & UCS \(=\)\(12.308\times\text{BTS}^{1.0725}\) & Power & 0.95 \\ [PERSON] and [PERSON] [77] & Various & UCS \(=\)\(7.73\times\text{BTS}^{1.197}\) & Power & 0.95 \\ [PERSON] and [PERSON] [98] & Sedimentary & UCS \(=\)\((12.4\times\text{BTS})-9\) & Linear & 0.87 \\ [PERSON] and [PERSON] [88] & Sedimentary & UCS \(=\)\(10.33\times\text{BTS}^{0.89}\) & Power & 0.97 \\ [PERSON] and [PERSON] [89] & Sedimentary & UCS \(=\)\((6.8\times\text{BTS})+13.5\) & Linear & 0.81 \\ [PERSON] [99] & Sedimentary & UCS \(=\)\((7.86\times\text{BTS})-447.63\) & Linear & 0.96 \\ [PERSON] et al. [90] & Sedimentary & UCS \(=\)\(7.53\times\text{BTS}\) & Linear & 0.67 \\ [PERSON] et al. [100] & Sedimentary & UCS \(=\)\(9.25\times\text{BTS}^{0.947}\) & Power & 0.95 \\ [PERSON] et al. [91] & Igneous & UCS \(=\)\((7.22\times\text{BTS})+40.08\) & Linear & 0.78 \\ [PERSON] and [PERSON] [92] & Igneous & UCS \(=\)\(6.75\times\text{BTS}^{1.08}\) & Power & 0.89 \\ [PERSON] et al. [93] & Various & UCS \(=\)\((15.361\times\text{BTS})-10.303\) & Linear & 0.91 \\ [PERSON] [94] & Metamorphic & UCS \(=\)\((10.03\times\text{BTS})+55.19\) & Linear & 0.96 \\ [PERSON] et al. [95] & Sedimentary & UCS \(=\)\((10.4\times\text{BTS})+18.2\) & Linear & 0.79 \\ [PERSON] [96] & Sedimentary & UCS \(=\)\((4.233\times\text{BTS})+13.64\) & Linear & 0.73 \\ [PERSON] [97] & Sedimentary & UCS \(=\)\((40.09\times\text{lnBTS})-36.14\) & Logarithmic & 0.97 \\ The present study & Igneous & UCS \(=\)\(11.905\times\text{BTS}\) & Linear & 0.81 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Correlation equations between UCS and BTS. For BTS classification, the equation developed between the UCS and BTS [Equation (2)] was rearranged as follows;  
\[\text{BTS }=\ 0.0840\times\text{UCS} \tag{5}\]  
In Equation (5), it is assumed that all the intrinsic characteristics, such as density, porosity, mineralogical composition, and textural parameters, of the studied igneous stone types are different. It can be seen from Equation (5) that there is a conversion factor of 0.0840 between BTS and UCS. In other words, the BTS values of the igneous stones are approximately 0.0840, on average, of the their UCS. Table 5 presents the values of the lower and upper limits of the UCS for each rock class in a UCS-based classification. These values were putted into Equation (5), and their corresponding BTS values were determined. Therefore, a BTS classification for igneous stones was developed. The BTS classification is shown in Figure 5. According to this figure, igneous stones are categorized into five classes: weak (Class I; BTS < 1.3 MPa), moderately weak (Class II; BTS 1.3-4.2 MPa), strong (Class III; BTS 4.2-10.1 MPa), very strong (Class IV; BTS 10.1-19.3 MPa), and extremely strong (Class V; BTS > 19.3 MPa). In both the UCS- and BTS-based classifications proposed by IAEG [87] and the present study, respectively, igneous stones are classified into five strength classes. These classifications can be used for description of qualitative-quantitative assessment of the igneous stones. However, there are significant differences between the UCS and BTS classifications. In the UCS-based classification, it is essential to prepare stone specimens with standard dimensions, a diameter of 54 mm and a length-to-diameter ratio of 2.5-3.0 [36].