Nagasaki Prefecture/Okime-Yashiro Tunnel Completed, Pushing for Early Opening; Built by Kumagai, Kadota, and Nakajima JV
Turning the Penetration Explosion Switch
Three Cheers to Celebrate the Breakthrough
The excavation of the Ogame-Yashiro Tunnel (896 meters long, from Ogame in Obama-cho, Unzen City to Kita-Arima-cho Otsu, Minamishimabara City), planned by Nagasaki Prefecture as part of the Obama-Kita-Arima Prefectural Main Road Improvement Project, has been completed, and a groundbreaking ceremony was held inside the tunnel on the 21st. The construction will be carried out by a joint venture of Kumagai Gumi, Kadota Construction, and Nakajima Construction. Attendees attended the ceremony to celebrate the completion and pray for the early opening of the improved road.
At the ceremony, Kondo Kazuhiko, Director of the Shimabara Development Bureau of the Prefecture, Tokunaga Tatsuya, Chairman of the Prefectural Assembly, Kanazawa Hidesaburo, Mayor of Unzen City, Matsumoto Masahiro, Mayor of Minamishimabara City, and Okaichi Mitsuji, Representative Director and Executive Vice President of Kumagai Gumi, activated the penetrating explosive switch. After the explosion, it was confirmed that the tunnel had been safely breached, followed by the purification ceremony of the breakthrough point, the opening ceremony, the mikoshi procession, and the sake barrel opening ceremony. In his speech as a client, Director Kondo expressed his gratitude to the contractor, saying, "I am very pleased that the tunnel, which is the main structure, was completed safely. I imagined that the tunnel excavation was extremely difficult due to the soft soil and large amount of boulders, but they were able to complete the construction safely thanks to their extensive experience and outstanding skills."
Speaking on behalf of the contractor, Vice President Okaichi said that the tunnel has a geological layer where lava flows from Mount Unzen Fugen occurred, and stated, "We encountered more difficulties than expected during the excavation, such as flowing spring water and collapsing excavation surfaces, but by making full use of the latest technology, we were able to complete the tunnel without any accidents." He added, "For the remaining construction works, we will continue to prioritize safety, quality, and the environment."
The 5.5m wide, 2-lane tunnel was constructed using the NATM (Natural Machined Excavation) method, with an internal cross-sectional area of 52 to 56m2. Excavation work began at the starting point in late May 2023, divided into two shifts, day and night, and took about 20 months to complete the tunnel. The construction period will last until November 30, 2025.
The improved road, including the tunnel, is expected to open to traffic around spring 2027. When it opens, the sharp turns and irregular intersections on the current route will no longer be required, which is expected to bring the benefits of enhancing access to the central area of the province and improving road safety.
