## 3 Experimental Results and Discussion  
### Effect of Joints on Cutting Force  
To investigate the effect of joints on \(FC\), unrelieved cutting tests were performed by varying the distance between the cutting path and the joint plane (\(d\)) from 0.1\(J_{s}\) to 0.5\(J_{s}\), corresponding to \(d\) values ranging from 3 mm to 45 mm depending on joint spacing. The analysis was based on \(FC_{m}\), and the values obtained from cutting tests for each joint spacing are summarized in Tables 2-  
Figure 7 shows the relationship between d and \(FC_{m}\). It should be noted that the cutting depth of 3 mm was tested only under the 30 mm joint spacing. Since this limited the maximum d to just 15 mm, the data point was excluded from Figure 7, as it does not provide a sufficient basis for generalizing the trend of \(FC_{m}\) with respect to \(d\). It can be seen from Figure 7 that \(FC_{m}\) decreases with increasing d up to a certain point and then increases thereafter. In addition, when cutting is performed at the midpoint between joint planes (\(d=0.5J_{s}\)), \(FC_{m}\) shows consistent values for each cutting depth, regardless of joint spacing. For example, in the cutting test with a depth of 6 mm (Figure 7a), \(FC_{m}\) was 4.91 kN at \(d=3\) mm, decreased to a minimum of 4.02 kN at \(d=9\) mm, and then increased to 4.57 kN at \(d=15\) mm (\(0.5J_{s}\)) for the 30 mm joint spacing. Similar trends were observed for joint spacings of 60 mm and 90 mm, where \(FC_{m}\) at \(d=0.5J_{s}\) was 4.86 kN and 4.80 kN, respectively, showing comparable values. It is noted that the \(FC_{m}\) values at \(d=0.5J_{s}\) were very close to those observed in intact rock cutting at the same cutting depth (approximately 4.6 kN for 6 mm). This suggests that the influence of joints becomes negligible when the cutting path is positioned at the midpoint between joint planes. This consistent trend was also observed at cutting depths of 9 mm and 12 mm (Figure 7b,c), further supporting the interpretation that joint effects are minimal at \(d=0.5J_{s}\). \begin{table}
\begin{tabular}{c c c c c c} \hline \(p\) (mm) & \(d\) (mm) & \(d\)/\(J_{s}\) & \(d\)/\(p\) & \(FC_{m}\) & **Normalized \(FC_{m}\)** \\ \hline
6 & 6 & 0.1 & 1 & 4.10 & 0.89 \\  & 12 & 0.2 & 2 & 3.52 & 0.77 \\  & 18 & 0.3 & 3 & 3.61 & 0.79 \\  & 24 & 0.4 & 4 & 3.55 & 0.77 \\  & 30 & 0.5 & 5 & 4.86 & 1.06 \\
9 & 6 & 0.1 & 0.67 & 7.60 & 1.04 \\  & 12 &Therefore, to examine the general relationship between \(FC_{m}\) and d independent of joint spacing, a regression curve was fitted using all data points except those at \(d=0.5\)\(J_{s}\), where joint effects were considered negligible. The results confirmed that \(FC_{m}\) and d exhibit a quadratic relationship for all cutting depths. All fitted regression curves were statistically significant at the 99% confidence level, as the \(R^{2}\) values were greater than 0.5, the \(F\)-values exceeded 5, and the \(p\)-values were less than 0.05. Notably, \(FC_{m}\) reached its minimum value at approximately \(d=20\) mm across all cutting depths, suggesting that joint effects are most significant within this range. When viewed in terms of the ratio \(d/p\), the minimum \(FC_{m}\) was found to occur at lower \(d/p\) values as the cutting depth increased. Considering that the optimal ratio of line spacing to cutting depth (\(s/p\)) for achieving high cutting efficiency with conical picks under relieved cutting conditions typically ranges between 2 and 5 [38], this trend implies that the relative influence of joints tends to decrease as the cutting depth increases. The effect of distance on cutting force, considering joint spacing, was examined by analyzing the correlation between normalized \(FC_{m}\), which represents the ratio of the mean cutting force in jointed rock to that in intact rock under the same cutting depth, and the ratio \(d/J_{s}\) was analyzed. As shown in Figure 8, a statistically significant correlation was observed between normalized \(FC_{m}\) and \(d/J_{s}\).