RAM measure of EPB shield tunneling system under uncertain parameters – A case study in Tehran metro line 6

Tunnels have a crucial role in preventing traffic jams in cities' transportation systems. Therefore, their timely design and construction are fundamental. The past decade has seen the rapid development of Earth Pressure Balance (EPB) machines as the most efficient and safest boring machines in urban areas with the lowest surface subsidence. Nevertheless, despite their numerous benefits, using these machines has disadvantages, such as long-term downtimes and heavy maintenance costs that the projects suffer from. Recently, there has been a surge of interest among researchers in troubleshooting and reducing the downtime of this complex machine. This paper mainly aims to trace and estimate executive elements' impact on machine reliability. To this end, all stops related to 16 subsystems over 12 months were collected and divided into two scenarios, direct (technical) and indirect (technical and executive) factors. According to the results obtained from the preliminary analysis of the raw data: (1) no substantial executive elements were recorded for the navigation subsystem; (2) the trend and serial correlation tests indicated that all Time Between Failures (TBFs) and Time To Repairs (TTRs) from subsystems followed the renewal processes, except for the navigation subsystem's TTR data that followed the non-homogenous poison process (NHPP); (3) the conveyor and segment subsystems were jointly introduced as the most critical subsystem with indirect factors; (4) in contrast, the conveyor subsystem with direct factors was found as the most critical one from the reliability point of view; and (5) the most striking result obtained from the data was that the executive elements could reduce the overall reliability of the EPB machine by about 40 % compared to the contrary scenario.