The Seikan Tunnel is a long undersea tunnel connecting Honshu and Hokkaido. Excavation of the tunnel began in 1964 and was put into service 24 years later in 1988. Since 2016, this line has been running on a three-track gauge, which is rare in the world, and has been running on the Shinkansen and conventional lines. Even now, 35 years after its opening, the Seikan Tunnel is still used as an important trunk line connecting Honshu and Hokkaido. In this paper, we describe the maintenance and management of the Seikan Tunnel.

 In bridge maintenance management based on close-up visual inspection, it is difficult to fully understand the deterioration and damage occurring inside the structure. One of the methods to solve this problem is the use of monitoring technology using acceleration sensors. This paper reports on an approach to the introduction of bridge maintenance management using monitoring technology based on acceleration sensors, focusing on areas where deterioration and damage are difficult to be detected by close-up visual inspection.

 Ultra-high-strength fiber reinforced concrete (UFC) is a popular strengthening material for deteriorated reinforced concrete structures. In this study, an effective reinforcement method was developed for RC columns with corrosion damage. The cracked cover concrete (50 mm thick) of RC columns was replaced with UFC, and positive and negative cyclic loading tests were carried out with an axial stress of 1 MPa. The experimental results demonstrated that the maximum load-bearing capacity of the damaged specimen retrofitted with UFC reinforcement exceeded that of the reference specimen, confirming the effectiveness of this method.

 This bridge is located above the Shinkansen tracks, and there are time constraints from the last train to the first train and the environmental constraints of the dense concentration of Shinkansen equipment, so we examined and implemented the issues and successfully completed the removal work.

 This report describes an initiative aimed at training young civil engineers who will be involved in infrastructure maintenance work in the future by having university students and faculty accompany and collaborate with local government infrastructure maintenance work, as well as developing methods that will contribute to inexpensive, simple, and effective inspection and diagnosis. Since 2021, the Department of civil engineering at Kokushikan University has continuously organized a team of several fourth-year students to carry out inspections and organize data under the guidance of staff from Ome City's Civil Engineering Department. Through these activities, methods for inspecting from below girders using simple handheld devices, creating drawings for bridges without as-built drawings, ranking pavement damage at intersections, and creating simple GIS databases have been tried and proposed.