## 4 Conclusions  
A series of rock cutting tests was conducted using a conical pick to investigate the effect of joints on the performance of roadheaders. Rock cutting tests were performed on intact rock specimens and jointed rock mass specimens with three different joint spacings. Through these tests, the influence of the angle between the joint plane and the cutting direction, as well as joint spacing, on the cuttability of the conical pick was investigated. The cuttability of the conical pick was shown to be improved in jointed rock mass compared to intact rock. The behaviour of \(FC\) in each individual cut within a series of cuts provided insight into the mechanisms through which joints contribute to enhanced cuttability. When cutting perpendicular to the joint plane, the presence of joints shortens the required fracture length for rock chip formation, reducing \(FC\). In the parallel cutting direction, the joint plane acts as a barrier to side-crack propagation, lowering the \(FC\) required for crack development. \(FC\) and \(SE\) were generally lower when cutting parallel to the joint plane compared to cutting perpendicular to it. However, when the cutting depth exceeded 0.2 times the joint spacing and the line spacing surpassed 0.4 times the joint spacing, the opposite trend was observed. This is because, as the cutting depth increases and the line spacing becomes larger while the joint spacing remains constant, the joints hinder the interaction between adjacent cuts, leading to a gradual transition to an unrelieved cutting mode. Additionally,  
Figure 21: Variation in \(s/p_{\text{opt}}\) with \(J_{s}\). _FC_ and _SE_ increased with joint spacing, and at a joint spacing 10 times the cutting depth, they exhibited values similar to those in intact rock. This indicates that when the joint spacing exceeds 10 times the cutting depth, the influence of joints becomes negligible. The findings of this study provide a better understanding of the influence of joints on the performance of roadheaders. However, this study is limited in its consideration of diverse joint conditions, particularly joint orientation. Therefore, to expand these findings, future work will include experimental investigations that consider joint orientation, as well as numerical simulations, to explore a broader range of joint characteristics and complex conditions involving joint sets. Conceptualization, H.-E.K. ; methodology, H.-E.K. ; investigation, H.-E.K. ; data curation, H.-E.K. ; writing--original draft preparation, H.-E.K. ; writing--review and editing, M.-S.K., W.-K.Y. and C.-Y.K. All authors have read and agreed to the published version of the manuscript. This work was supported by the Korea Agency for Infrastructure Technology Advancement (KAIA) grant funded by the Ministry of Land, Infrastructure, and Transport (grant RS-2024-00416524, development of technology to enhance safety and efficiency of ultra-long K-underground expressway infrastructure). Not applicable. The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author. The authors declare no conflicts of interest. +++ ==WARNING: Truncated because of repetitions==
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