## 7 Conclusions  
This paper presented a complete database of TBFs and TTRs for three subsystems (electrical, mechanical, and cutterhead) of the EPBMs in Lines 1 and 2 of the Isfahan metro project. Two methods have been used to find the availability A(t) of the EPBM. The results show that the Markov process is more appropriate for deriving the availability of the EPBMs, especially when comparing systems with different subsystems. Further analysis of reliability R(t) and maintainability M(t) show that the Markov process cannot satisfy the processes where the probability density functions of the time between failures of the EPBM (TBFs) and the required time to carry out repairs (TTRs) are not exponentially distributed.  
For the RAM analysis of the EPBMs in Lines 1 and 2, the following key findings were identified:  
1. R(t), A(t), and M(t) of the system are dependent on its subsystems. For the EPBMs of the Isfahan metro, the mechanical and cutterhead subsystems have the most significant effect on the system's R(t) and M(t), respectively.
2. The PM has a more substantial effect on the mechanical subsystem. For the reliability level of 80%, the PM plan has improved the excavation time from 0.4 h for Line 1 to 0.8 h for Line 2.
3. Since the M(t) of the system is close to the M(t) of the cutterhead, obtaining the same cutterhead M(t) for Lines 1 and 2 resulted in the same M(t) for the whole system for both lines. This means that refurbishing the cutterhead has been effective despite no change in the M(t) values between the lines. If there had been no refurbishment in the cutterhead for Line 2, its M(t) would have probably been worsened than Line 1 due to the existence of mixed face (i.e., rock and soil) in Line 2.
4. The PM also had a significant effect on the availability of the system. The availability of 45% during the construction of Line 1 has increased to 61% for Line 2 after applying PM.
5. It is recommended that for future works, an investigation be conducted on the application of other methods, such as the proportional hazard model (PHM), stratified Cox regression model (SCRM), and mixture proportional hazard model (MPHM) in EPBM projects. One of the main features of these methods is their ability to evaluate the impact of various environmental risk factors on the system's performance, which would provide an even more comprehensive analysis.  
Conceptualization, A.K. and S.M.; Data curation, A.K.; Formal analysis, A.K., R.K., S.M. and M.H.; Investigation, A.K., R.K. and S.M.; Methodology, A.K., S.M. and M.H.; Project administration, S.M. and M.H.; Resources, A.K., and S.M.; Supervision, M.H.; Validation, A.K., R.K., S.M. and M.H.; Visualization, A.K. and S.M.; Writing--original draft, A.K. and S.M.; Writing--review and editing, R.K.; M.H. and B.V. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research was funded by the Advanced Construction and Sustainable Futures research cluster at the School of Future Environment, Auckland University of Technology with funding number R12387.01 DS-281.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** Data that support the reported results will be available by contacting the corresponding author upon reasonable request.  
**Acknowledgments:** The authors thank the Isfahan Urban Railway Organization, Zayandab Consultant Company, and Farbar Consultant Company for their support, and Sabir International Company for their assistance in the research.  
**Conflicts of Interest:** The authors declare no conflict of interest.