Iwate-Ichinohe Tunnel

The Iwate-Ichinohe Tunnel (岩手一戸トンネル) is a 25.810 kmcite journal| author=Yamaji, H. | title= [http://www.jsce.or.jp/English/Publication/CivilEng/2001/longest.pdf World's Longest Terrestrial Railway Tunnel] | journal= jsce-int.org | year=2001 ] terrestrial railway tunnel in Japan — part of the Tōhoku Shinkansen, linking Tokyo with Aomori. When opened in 2002 it was the longest terrestrial (land based) tunnel in world, but was overtaken by the Lötschberg Base Tunnel in June 2007.

The tunnel is located 545 km away from Tokyo Station on the Tōhoku Shinkansen line, midway between Morioka and Hachinohe. Surveying commenced in 1988. In 1991 construction began, and the tunnel holed through in 2000. The tunnel became operational when the railway line opened in 2002. Maximum depth is about 200 m.

Geography and geology

The tunnel passes through hilly terrain near the Kitakami and Ou mountains. The Mabuchi and Kitakami rivers run near the tunnel's Toyko portal.

Geology along the tunnel route can be divided into three sections:
*17 km from the Tokyo end: Mesozoic and Paleozoic strata (argillite, granodiorite, hornfels and chert)
*5 km central section: Neogene volcanic tuff, which was susceptible to swelling and caused engineering difficulties.
*4 km from the Aomori end: a combination of the previous two sections, as well as mudstone and andesite of the Neogene period.Faults cross the path of the tunnel.

Engineering

The tunnel is a single bore twin track design. A horseshoe shape, the cross-sectional dimensions are: 9.8 (width) x 7.7 m (height) (an excavated area of approximately 70 to 85 m²). It rises at a gradient of 0.5% from the Toyko portal for approximately 22 km, then drops at a gradient of 1% down to the Amori portal. The New Austrian Tunnelling method (NATM) was adopted to cope with the geology. NATM techniques deployed included rock bolts, shotcrete and steel supports. Excavation methods were dependent on the geology, drill and blast or mechanical excavation and full face or bench cut methods were used. To speed up and reduce the costs of construction the tunnel was divided into seven sections, with intermediate access ramps or inclined shafts.

References