On the eve of a century since the construction of the national railway in Iran, there are still routes that have been operated in the same way since their opening; tunnels constitute an important part of these strategic routes that require a comprehensive and systematic study. The present study was conducted to select the optimal plan for improving and strengthening old tunnels. The South Tehran Railway axis was selected as the study case of this study, and after studying this route, Tunnel No. 68 (Kashor Tunnel) was selected as a control sample due to the difference in the variety of geomechanical properties. This tunnel was modeled by geotectonic studies conducted by the FLAC^3D numerical software, and the most critical section was examined to study the effect of adding conventional maintenance systems on tunnel safety. In order to study safety, only studies were conducted on the critical section in such a way that 47 maintenance systems were simulated and analyzed in the FLAC^3D software to examine the safety factor. In the next stage, the implementation cost of each system was calculated by experts in terms of "installation time and lack of conflict with operation" and "implementation capability" of maintenance, and quantitative factors were determined and optimized in a multivariate manner using the TOPSIS fuzzy model.