Unveiling the Giant Metal Fortress: A Rare Glimpse into the Kitanomaki Tunnel Construction Site

The Kitanomaki Tunnel, frequently described as a giant metal fortress, opened its doors to a select few lottery winners for a rare glimpse inside. In Gunma, Japan, this ongoing construction project aims to prevent rockfalls above the Joshin-Etsu Expressway in Annaka City.

(Photo : Japan Forward/Takumi Kamoshida)

Glimpse of Kitanomaki Tunnel Construction Site

On Sunday, June 16, approximately 70 individuals were chosen to tour the Kitanomaki Tunnel construction site through a lottery. As mentioned, guests reportedly had the opportunity to ride the construction monorail, explore the excavation site, and see the heavy gear, including a massive crane. Wearing helmets, participants climbed the scaffolding while the tour was in progress. Accordingly, a massive scaffolding structure roughly 50 meters high conceals the steep slope. They had a pleasant view of the area's road and mountains.

Since 2017, this project has been ongoing. Work starting in February 2023 aimed at removing the rock mass above the tunnel. To mitigate rockfall above the Kitanomaki Tunnel on the Joshin-Etsu Expressway in Annaka City, East Nippon Expressway Co. is currently engaged in construction activities. Moreover, the construction project is expected to finish by 2029. The tunnel, spanning 190 meters, was opened in 1993 with its entrance located on the Nagano Prefecture side. Due to the multiple layers of scaffolding erected for drilling work during the rock-removal process, the rock face achieved the appearance of a fortress.

In 1996, a rockslide in a tunnel in Hokkaido began safety inspections of tunnels across the country. Kitanomaki Tunnel has been identified as having a potential for rockfall. In 2014, a decision was made to implement a policy to remove the rock face, and in 2017, preparation work started.

Following the completion of the drilling process, portions of the rock will be removed from the tunnel's backside beginning in May. The project is anticipated to remove approximately 95,000 cubic meters of rock over five years. Nevertheless, the rock removal process has resulted in the construction of specialized roadways and an elevator capable of loading two huge trucks.

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Purpose of Tunnel Scaffolding

The components of tunnel scaffolding are indistinguishable from those of regular tubing and fitting scaffolding. Tunnel scaffolds are frequently utilized in construction work in situations where there is inadequate headroom or if the use of these scaffolds is restricted due to the presence of congested regions.

With horizontal beams supported on horizontal beams equal to or less than three meters apart, they typically consist of two standard 'A' frames to support the scaffolding. When there is insufficient ground clearance for traditional scaffolding, tunnel scaffolding is frequently used in construction. This type of scaffolding is used during earthworks and on steep slopes. Like ordinary tube and fitting scaffolding, tunnel scaffolding comprises the same components. Tunnel scaffolds are frequently utilized in construction work in situations where there is insufficient headroom or if the use of these scaffolds is restricted due to the presence of congested regions.

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