Development of Maintenance Indicator to Evaluate Soundness of Subway Tunnels

Tokyo Metro ensures the safety of underground tunnels as civil engineering structures by conducting inspections and performing appropriate repairs. Inspections are generally conducted visually, and health grades are determined according to the extent of deformations. However, given the difficulty of comparing the health grades of sections within the structures to the same standards throughout entire lines, locations that require long-term countermeasures in terms of maintenance were often selected and ranked according to knowledge acquired intuitively by employees with experience, and qualitative judgments based on comprehensive perspective of multiple survey results. To address this issue, we developed an inspection item response model (mathematical model) in which inspection data is used to calculate maintenance indicators in an attempt to quantify health grades of sections within the structures. For estimations, we used Bayesian estimators based on Markov chain Monte Carlo methods. This report presents an overview of indicator estimations as well as the process and results of those estimations.