## 3 Results and Discussions
### Abrasivity of Rock  
Figure 11 shows the relationship between the CAI and brittleness indices. The results are presented by grouping based on the rock's geological origins. Overall, no significant relationship was found between the brittleness indices and CAI. For B1 and B2, CAI roughly increases with the brittleness of rock for the igneous and sedimentary rocks, while it also roughly decreases in metamorphic rocks. This finding means that the abrasiveness of rock depends on properties other than the strength property of rock, and implies that rock abrasiveness may vary depending on a rock's geological origin. The statement can be supported by the previous study [42]. They stated that different correlations between geomechanical properties and CAI were found according to the origin of rocks. Because \begin{table}
\begin{tabular}{c c} \hline
**Input Parameters** & **Equations** \\ \hline B3, p, S & \(\text{SE}=1.16\times\text{p}^{0.11}\times\text{S}^{-0.36}\times\text{B}_{0} ^{0.496}\) (R2 = 0.44) \\ B4, p, S & \(\text{SE}=1.09\times\text{p}^{0.21}\times\text{S}^{-0.37}\times\text{B}_{0} ^{0.322}\) (R2 = 0.47) \\ UCS, p, S & \(\text{SE}=1.07\times\text{p}^{0.15}\times\text{S}^{-0.37}\times\text{UCS}^{0.4 56}\) (R2 = 0.43) \\ UCS, BTS, p, S & \(\text{SE}=0.75\times\text{p}^{0.16}\times\text{S}^{-0.35}\times\text{UCS}^{0.3 7}\times\text{BTS}^{0.27}\) (R2 = 0.47) \\ \hline \end{tabular}
\end{table} 
Table 6: Prediction models for specific energy under optimum conditions. the main mineral composition depends on the origin of rocks, it is thought that these differences in mineral composition lead to different trends in the relationship between the abrasiveness of rock and several properties of rock. However, in this study, the relationships were found to not be consistent in the current research database. This means that it is challenging to estimate rock abrasivity with only the rock brittleness, which is expressed by the rock strength. On the other hand, Figure 12 shows the relationship between CAI and EQC. A significant linear relationship was found between the CAI and EQC. As reported by the previous studies [21; 34; 35; 42], this indicated that the equivalent quartz content (EQC) is highly correlated with the rock abrasivity. However, conflicting findings have been also reported by other previous studies; [PERSON] and [PERSON] [20] stated that rock strength is the most influencing factors on the CAI value, while [PERSON] [22] reported that any significant correlation between CAI and EQC was not obtained. It is presumed that the tested rock types could affect the CAI values, which also means that other properties of rock (e.g., porosity, mineral composition, grain size, etc.) could affect the rock abrasivity. However, this cannot be concluded with the current findings. Figure 10: The relationships between optimum s/p ratio and brittleness indices: (**a**) S/p(opt)–B\({}_{1}\); (**b**) S/p(opt)–B\({}_{2}\); (**c**) S/p(opt)–B\({}_{3}\); (**d**) S/p(opt)–B\({}_{4}\). In Table 7, the regression models used to predict the CAI values based on the EQC and brittleness indices are shown. All prediction models showed similar performance for predicting the CAI values. Furthermore, the UCS model showed a similar level of performance compared to the brittleness indices model, indicating that the BTS played no significant role in predicting the CAI values. These results were consistent with the findings of previous studies [34; 35]. Although the rock abrasivity and mineral composition  
Figure 11: The relationships between the Cerchar abrasiveness index and brittleness indices: (a) CAI–B\({}_{1}\); (b) CAI–B\({}_{2}\); (c) CAI–B\({}_{3}\); (d) CAI–B\({}_{4}\). Figure 12: The relationships between the Cerchar abrasiveness index and equivalent quart content: fitting for (a) each rock origin, and (b) all rock types. can be useful indicators to estimate the cutter wear, the properties are usually measured from the homogeneous rock specimen, while the tested rocks in this study are limited in isotropic rocks.