Evaluation of reliability, availability and maintainability of back-up locomotives in earth pressure balance tunnel boring machine (EPB-TBM): A case study: Tabriz Metro Line 1

Back-up locomotives are locomotives responsible for mechanized excavation of tunnels, transport of prefabricated concrete parts, slurry poured behind prefabricated concrete parts and foams, as well as materials excavated from the tunnel. In this study, the reliability, availability and maintainability of back-up locomotives of EPB-TBM machines of Tabriz metro line 1 have been investigated. Initially, locomotives were divided into four main systems, including pneumatic, electrical, hydraulic and motor. Each of these systems, in turn, consisted of subsystems. Then, the failure data of 5 locomotives were collected; after combining the data, about 30,000 hours of data were obtained from the failures. Examination of the data showed that there was a failure in ten subsystems and these subsystems were critical. Pareto analyzes were then performed to examine the percentage of failures, costs, and repair times. For each subsystem, the most appropriate failure distribution function was fitted and the reliability of the subsystems and systems was determined. Due to the lack of a trend in all failure data and the prevalence of independent and equal conditions for the data, reliability and availability were matched. Also, using the average repair times, the maintainability of the components was determined. The results indicated the importance of reliability for pneumatic, electrical, motor and hydraulic systems, respectively. Meanwhile, the pneumatic system is very different from the other three systems, and over time, this difference becomes even greater. Another very important result is the loss of reliability of almost all subsystems to below 50% after 500 hours of operation. In the maintenance section, the results also showed that all failure times were higher than 400 hours. In terms of repair times, a significant part was related to the hydraulic system, followed by the engine and pneumatic system with the most repair time.