The undergrounding will take place for approximately 1.8 km from Kandabashi JCT to Edobashi JCT, using the route to the Yaesu Line (Y) from Kandabashi JCT, going underground, branching off near Isshibashi Bridge, coming out to the surface near Edobashi Bridge, and returning to the main line at Edobashi JCT. With the undergrounding, the entrances at Tokiwa-bashi, Gofukubashi, and Edobashi have been eliminated.
Initially, the plan was to replace the current concrete slab with a steel slab, but in 2016, three areas around Nihonbashi were added to the “Urban Revitalization Project” of the National Strategic Special Zone, and from the following year, 2017, the undergrounding was considered together with the surrounding urban development. By utilizing the “multi-level road system,” which allows buildings to be constructed in the space above and below the road site, it was decided to move the main line underground and remove the elevated road to restore the sky around the Nihonbashi area and improve the landscape and environment.
The Takebashi JCT to Edobashi JCT (approx. 2.9 km) of the Tokyo Loop Line (C1) was put into service before the Tokyo Olympics in 1964, and more than 50 years have already passed since its construction. In addition, it is heavily damaged due to traffic volume of approximately 100,000 vehicles per day. In addition, the Kandabashi JCT – Edobashi JCT is an elevated bridge over the Nihombashi River, which requires boats for maintenance and management. For these reasons, a large-scale work was diagnosed as necessary in the renewal plan.
More than 60% of the total 327.2 km length of the road has been in service for more than 30 years, and the structures are aging, with damage to rope girders and concrete slabs becoming apparent. Therefore, the “Metropolitan Expressway Renewal Plan” was released in 2013. As part of the “Expressway Renewal Project,” large-scale renewal and repair projects are underway on the Haneda Line (Metropolitan Expressway No. 1) and the Shibuya Line (Metropolitan Expressway No. 3).
Removal of entrances and exits, the first step toward undergrounding, is underway.
Mr. Ikuro Kusakabe, Director of the Nihonbashi Project Promotion Department, Metropolitan Expressway Renewal and Construction Bureau, gave an overview at the site of the former Edobashi entrance, where the Nihonbashi underground project is underway.
He stated that this construction section had been in operation for about 60 years since 1963, and that it was severely damaged due to the approximately 100,000 vehicles per day of cross-sectional traffic, and that the project was initiated in FY2014 as a “large-scale repair project. He then described how the redevelopment project around the Nihonbashi area was positioned as an urban revitalization project, which led to the decision to underground the section in conjunction with urban development, and commented, “Once the undergrounding project is completed, we expect to renew the Metropolitan Expressway, as well as improve the surrounding environment and enhance the attractiveness of the area.
The current progress is in Phase 1, “removal of entrances and exits,” with construction starting in April 2021, and closing the entrances and exits of the Edobashi and Gofukubashi bridges in May. On the day of the interview, the girders were being removed, and after their removal, the main construction work will finally begin. He stated his future plans, “We will complete the underground route in 2035, followed by the removal of the elevated structure over the next five years.”
Mr. Jun Emizu, Manager, Nihonbashi Project Coordination Division, Metropolitan Expressway Renewal and Construction Bureau, then gave an overview of the project.
The total length of the Nihonbashi section underground project is 1.8 km, of which the tunnel portion is 1.1 km. looking from Kandabashi JCT, the route uses about 100 m of the existing Yaesu Line to enter the newly built tunnel section, and then goes through a tunnel using open-cut and shield construction methods, a retaining wall and an elevated bridge to Edobashi JCT. 1 deepest The route, which is about 20 m underground by the way, is said to be like “going through the eye of a needle,” dodging the Ginza and Asakusa subway lines. He commented, “This is the first time that urban development and infrastructure improvement are being carried out simultaneously over a long period of time, and is a new model case of urban renewal.
The current progress is the removal of the entrance and exit, because the tunnel is located under the current piers. While removing the piers in this area first, temporary piers will be installed in areas that will not interfere with tunnel excavation in the main line section, and then tunnel construction will begin. He stated that completion of this removal work in FY2023 will “return about 10% of the blue sky.
Next, the tour moved to the site where the bridge girders were being removed. Mitsumasa Osada, Director of the Nihonbashi Construction Office, Metropolitan Expressway Renewal and Construction Bureau, explained the bridge girder removal work on board the ship. In this work, two bridge girders for one span are cut, one of which is suspended by two jacks on each side for a total of four jacks, and lowered into a barge on the river by shrinking it by approximately 50 cm 20 to 30 times. The lowering of one bridge girder takes about 3.5 hours, and after two girders are lowered, they are divided into six pieces for loading onto trucks for removal. The remaining bridge girders will be removed in the future, and the removal of the entrance and exit is scheduled for completion at the end of FY2023.
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