The Seikan Tunnel ( ja, 青函トンネル, or , ), is a

dual-gauge In railway engineering, "gauge" is the transverse distance between the inner surfaces of the heads of two rails, which for the vast majority of railway lines is the number of rails in place. However, it is sometimes necessary for track to ca ...

railway tunnel in Japan, with a portion under the seabed of the

Tsugaru Strait The is a strait between Honshu and Hokkaido in northern Japan connecting the Sea of Japan with the Pacific Ocean. It was named after the western part of Aomori Prefecture. The Seikan Tunnel passes under it at its narrowest point 12.1 miles (1 ...

, which separates

Aomori Prefecture is a prefecture of Japan in the Tōhoku region. The prefecture's capital, largest city, and namesake is the city of Aomori. Aomori is the northernmost prefecture on Japan's main island, Honshu, and is bordered by the Pacific Ocean to the eas ...

on the main Japanese island of

Honshu , historically called , is the largest and most populous island of Japan. It is located south of Hokkaidō across the Tsugaru Strait, north of Shikoku across the Inland Sea, and northeast of Kyūshū across the Kanmon Straits. The island se ...

from the northern island of

Hokkaido is Japan's second largest island and comprises the largest and northernmost prefecture, making up its own region. The Tsugaru Strait separates Hokkaidō from Honshu; the two islands are connected by the undersea railway Seikan Tunnel. The lar ...

. The track level is about below the seabed and below sea level. The tunnel is part of the standard-gauge

Hokkaido Shinkansen The is a Japanese high-speed Shinkansen rail line that links up with the Tōhoku Shinkansen in northern Aomori Prefecture in Honshu and continues on into the interior of Hokkaido through the undersea Seikan Tunnel. Construction started in May ...

and the narrow-gauge Kaikyō Line of the

Hokkaido Railway Company The is one of the constituent companies of the Japan Railways Group (JR Group), and is often referred to using its official abbreviation of . It operates intercity and local rail services in Hokkaido, Japan. The company introduced Kitaca, a s ...

(JR Hokkaido)'s Tsugaru-Kaikyō Line. The name ''Seikan'' comes from combining the ''

on'yomi are the logographic Chinese characters taken from the Chinese script and used in the writing of Japanese. They were made a major part of the Japanese writing system during the time of Old Japanese and are still used, along with the subsequ ...

'' readings of the first characters of , the nearest major city on the Honshu side of the strait, and , the nearest major city on the Hokkaido side. The Seikan Tunnel is the world's longest undersea tunnel by overall length (the Channel Tunnel, while shorter, has a longer undersea segment). It is also the second-deepest transport tunnel below the sea level after the

Ryfylke Tunnel The Ryfylke Tunnel ( no, Ryfylketunnelen) is an undersea road tunnel in Rogaland county, Norway. It is part of the Norwegian National Road 13 running between Stavanger and Ryfylke (district) under the Horgefjord (part of the Boknafjord). The ...

, a road tunnel in Norway which opened in 2019, and the second longest main-line railway tunnel after the

Gotthard Base Tunnel , rm, Tunnel da basa dal Sogn Gottard , image = 20141120 gotthard-basistunnel02-wikipedia-hannes-ortlieb.jpg , image_size = 250 , caption = Turnout at Faido multifunction station , line = Gotthard Line , location = Switzerland ( Uri, Grisons and ...

in Switzerland, opened in 2016.

History

Connecting the islands

and

by a fixed link had been considered since the Taishō period (1912–25), but serious surveying commenced only in 1946, induced by the loss of overseas territory at the end of World War II and the need to accommodate returnees. In 1954, five ferries, including the '' Tōya Maru'', sank in the Tsugaru Strait during a typhoon, killing 1,430 passengers. The following year,

Japanese National Railways The abbreviated JNR or , was the business entity that operated Japan's national railway network from 1949 to 1987. Network Railways As of June 1, 1949, the date of establishment of JNR, it operated of narrow gauge () railways in all 46 pref ...

(JNR) expedited the tunnel feasibility study. Also of concern was the increasing traffic between the two islands. A booming economy saw traffic levels on the JNR-operated Seikan Ferry double to 4,040,000 passengers/year from 1955 to 1965, and cargo levels rose 1.7 times to 6,240,000 tonnes/year. Inter-island traffic forecast projections made in 1971 predicted increasing growth that would eventually outstrip the ability of the ferry pier facility, which was constrained by geographical conditions. In September 1971, the decision was made to commence work on the tunnel. A

Shinkansen The , colloquially known in English as the bullet train, is a network of high-speed railway lines in Japan. Initially, it was built to connect distant Japanese regions with Tokyo, the capital, to aid economic growth and development. Beyond l ...

-capable cross section was selected, with plans to extend the Shinkansen network. Arduous construction in difficult geological conditions proceeded. Thirty-four workers were killed during construction. On 27 January 1983, Japanese Prime Minister

Yasuhiro Nakasone was a Japanese politician who served as Prime Minister of Japan and President of the Liberal Democratic Party from 1982 to 1987. He was a member of the House of Representatives for more than 50 years. He was best known for pushing through the ...

pressed a switch that set off a blast that completed the

pilot tunnel A tunnel is an underground passageway, dug through surrounding soil, earth or rock, and enclosed except for the entrance and exit, commonly at each end. A pipeline is not a tunnel, though some recent tunnels have used immersed tube const ...

. Similarly on 10 March 1985, Minister of Transport Tokuo Yamashita symbolically bored through the main tunnel. The necessity for the project was questioned at times during construction, as the 1971 traffic predictions were overestimates. Instead of the traffic rate increasing as predicted to a peak in 1985, it peaked earlier in 1978 and then proceeded to decrease. The decrease was attributed to the slowdown in Japan's economy since the first oil crisis in 1973 and to advances made in air transport facilities and longer-range sea transport. The tunnel was opened on 13 March 1988, having cost a total of ¥1.1 trillion (US$7 billion) to construct, almost 12 times the original budget, much of which was due to inflation over the years. To commemorate the event, a commemorative 500 yen coin depicting the tunnel was issued by the

Japan Mint The is an Independent Administrative Institution of the Japanese government, responsible for producing and circulating the coins of Japan. The agency has its head office in Osaka with branches in Saitama and Hiroshima. The Japan Mint does not ...

in 1988. Once the tunnel was completed, all railway transport between Honshu and Hokkaido used it. However, for passenger transport, 90% of people use air travel due to the speed and cost. For example, to travel between

Tokyo Tokyo (; ja, 東京, , ), officially the Tokyo Metropolis ( ja, 東京都, label=none, ), is the capital and List of cities in Japan, largest city of Japan. Formerly known as Edo, its metropolitan area () is the most populous in the world, ...

and

Sapporo ( ain, サッ・ポロ・ペッ, Satporopet, lit=Dry, Great River) is a city in Japan. It is the largest city north of Tokyo and the largest city on Hokkaido, the northernmost main island of the country. It ranks as the fifth most populous cit ...

by train takes eight hours (Tokyo station and Shin-Sapporo station), with transfer from Shinkansen to narrow-gauge express train at Hakodate. By air, the journey is 1 hour and 45 minutes, or three hours and thirty minutes including airport access times. Deregulation and competition in Japanese domestic air travel has brought down prices on the Tokyo-Sapporo route, making rail more expensive in comparison. The ''

Hokutosei The was a limited express sleeping car train service in Japan which operated between Ueno Station in Tokyo and Sapporo Station in the northern island of Hokkaido, taking approximately 16½ hours. It was operated jointly by East Japan R ...

'' overnight train service began after the completion of the Seikan Tunnel; a later and more luxurious '' Cassiopeia'' overnight train service was often fully booked. Both were withdrawn following the commencement of

services (in August 2015 and March 2016 respectively), with freight trains being the only regular service utilising the narrow gauge line since that time. JR Hokkaido is exploring the use of "

Train on Train __NOTOC__ is a concept for piggybacking (that is, carrying narrow-gauge wagons on broader-gauge flatwagons) by the trainload rather than one wagon at a time. The need arose when Japan's Hokkaido Railway Company (JR Hokkaido) was planning f ...

" technology to remove the threat that the

shock wave In physics, a shock wave (also spelled shockwave), or shock, is a type of propagating disturbance that moves faster than the local speed of sound in the medium. Like an ordinary wave, a shock wave carries energy and can propagate through a me ...

created in front of Shinkansen trains traveling at full speed pose to freight trains operating on Japanese standard

narrow-gauge A narrow-gauge railway (narrow-gauge railroad in the US) is a railway with a track gauge narrower than standard . Most narrow-gauge railways are between and . Since narrow-gauge railways are usually built with tighter curves, smaller structu ...

track in a tunnel setting. If successful, it will allow the Hokkaido Shinkansen to travel at full speed inside the tunnel in the future. Shinkansen trains operate through the tunnel to Shin-Hakodate-Hokuto Station in

Hakodate is a city and port located in Oshima Subprefecture, Hokkaido, Japan. It is the capital city of Oshima Subprefecture. As of July 31, 2011, the city has an estimated population of 279,851 with 143,221 households, and a population density of 412.8 ...

, connecting Tokyo and Shin-Hakodate-Hokuto stations in four hours and two minutes, at a maximum speed of within the tunnel and outside it, and to the south of Morioka. It was expected that by 2018 one daily service will be run at through the tunnel. In March 2019, a 160 km/h speed limit inside the tunnel allowed Tokyo-Shin-Hakodate services in 3h58. The final stage is proposed to open to

Sapporo Station is a railway station in Chūō-ku, Sapporo, Hokkaido, Japan. It is served by Hakodate Main Line and other lines of Hokkaido Railway Company (JR Hokkaido), and is also connected to the Subway Sapporo Station. Sapporo Station is the starting p ...

in 2031 and is expected to shorten the Tokyo-Sapporo rail journey to five hours. The

will be operated by

JR Hokkaido The is one of the constituent companies of the Japan Railways Group (JR Group), and is often referred to using its official abbreviation of . It operates intercity and local rail services in Hokkaido, Japan. The company introduced Kitaca, a sm ...

Construction timeline

* 24 April 1946: Geological surveying begins. * 26 September 1954: The train ferry '' Tōya Maru'' sinks in the Tsugaru Strait. * 23 March 1964: Japan Railway Construction Public Corporation is established. * 28 September 1971: Construction on the main tunnel begins. * 27 January 1983: Pilot tunnel breakthrough. * 10 March 1985: Main tunnel breakthrough. * 13 March 1988: The tunnel opens. * 26 March 2016: Shinkansen services commence operation through the tunnel, regular narrow gauge passenger services through the tunnel cease.

Surveying, construction and geology

Surveying started in 1946 and construction began in 1971. By August 1982, less than 700 metres of the tunnel remained to be excavated. First contact between the two sides was in 1983. The

has eastern and western necks, both approximately across. Initial surveys undertaken in 1946 indicated that the eastern neck was up to deep with volcanic geology. The western neck had a maximum depth of and geology consisting mostly of sedimentary rocks of the Neogene period. The western neck was selected, with its conditions considered favourable for tunnelling. The geology of the undersea portion of the tunnel consists of volcanic rock, pyroclastic rock, as well as sedimentary rock of the Neogene period. The area is folded into a nearly vertical syncline, which means that the youngest rock is in the centre of the strait and encountered last. Divided roughly into thirds, the Honshū side consists of volcanic rocks (notably andesite and basalt); the Hokkaido side consists of sedimentary rocks (notably

Tertiary Tertiary ( ) is a widely used but obsolete term for the geologic period from 66 million to 2.6 million years ago. The period began with the demise of the non-avian dinosaurs in the Cretaceous–Paleogene extinction event, at the start ...

period

tuff Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is lithified into a solid rock. Rock that contains greater than 75% ash is considered tuff, while rock ...

and mudstone); and the centre portion consists of Kuromatsunai strata (Tertiary period sand-like mudstone). Igneous intrusions and faults caused crushing of the rock and complicated the tunnelling procedures. Initial geological investigation occurred from 1946 to 1963, which involved drilling the sea-bed, sonic surveys, submarine boring, observations using a mini-submarine, as well as seismic and magnetic surveys. To establish a greater understanding, a horizontal pilot boring was undertaken along the line of the service and main tunnels. Tunnelling occurred simultaneously from the northern end and the southern. The dry land portions were tackled with traditional mountain tunnelling techniques, with a single main tunnel. However, for the 23.3-kilometre undersea portion, three bores were excavated with increasing diameters respectively: an initial pilot tunnel, a service tunnel, and finally the main tunnel. The service tunnel was periodically connected to the main tunnel with a series of connecting drifts, at 600- to 1,000-metre intervals. The pilot tunnel serves as the service tunnel for the central five-kilometre portion. Beneath the Tsugaru Strait, the use of a

tunnel boring machine A tunnel boring machine (TBM), also known as a "mole", is a machine used to excavate tunnels with a circular cross section through a variety of soil and rock strata. They may also be used for microtunneling. They can be designed to bore thro ...

(TBM) was abandoned after less than two kilometres () owing to the variable nature of the rock and difficulty in accessing the face for advanced grouting. Blasting with dynamite and mechanical picking were then used to excavate.

Maintenance

A 2002 report by Michitsugu Ikuma described, for the undersea section, that "the tunnel structure appears to remain in a good condition." The amount of inflow has been decreasing with time, although it "increases right after a large earthquake". In March 2018 at 30 years of age, maintenance costs amounted to 30 billion Yen or US$286 million since 1999. Plans are to increase speed and provide mobile communication at the full track.

Structure

Initially, only narrow-gauge track was laid through the tunnel, but in 2005 the

project started construction which included laying dual gauge track (providing standard gauge track capability) and extending the

network through the tunnel. Shinkansen services to

commenced in March 2016, and are proposed to be extended to

by 2031. The tunnel has of

continuous welded rail A railway track (British English and UIC terminology) or railroad track (American English), also known as permanent way or simply track, is the structure on a railway or railroad consisting of the rails, fasteners, railroad ties (sleepers ...

. Two stations are within the tunnel— Tappi-Kaitei Station and Yoshioka-Kaitei Station. They serve as emergency escape points. In the event of a fire or other disaster, the stations provide the equivalent safety of a much shorter tunnel. The effectiveness of the escape shafts at the emergency stations is enhanced by having exhaust fans to extract smoke, television cameras to help route passengers to safety, thermal (infrared) fire alarm systems, and water spray nozzles. Before the construction of the Hokkaido Shinkansen, both stations contained museums detailing the history and function of the tunnel that could be visited on special sightseeing tours. The museums are now closed and the space provides storage for work on the Hokkaido Shinkansen. The two were the first railway stations in the world built under the sea. File:Seikan_Tunnel_entrance_-_dual-gauge_track.jpg, Entrance to the tunnel from Honshu side. The dual gauge tracks are visible File:Seikan-tunnel-yoshioka.jpg, Yoshioka-Kaitei Station platform in the Seikan Tunnel

References

External links

''The Seikan Tunnel''
Aomori Prefecture Government, version of 3 May 2006 at the

Internet Archive The Internet Archive is an American digital library with the stated mission of "universal access to all knowledge". It provides free public access to collections of digitized materials, including websites, software applications/games, music, ...

{{Authority control Coastal construction Railway tunnels in Japan Tunnels completed in 1988 Undersea tunnels in Asia Hokkaido Shinkansen 1988 establishments in Japan