Seikan Tunnel

Infobox tunnel
name = Seikan Tunnel 青函トンネル


caption = Map of the Seikan Tunnel.
line =
location = Beneath the Tsugaru Strait)
coordinates = coord|41.1932|140.1525|display=inline,title
system =
status = Active
start = Honshū
end = Hokkaidō
stations =
open = 13 March, 1988
owner = Japan Railway Construction, Transport and Technology Agency
operator = Hokkaido Railway Company
character =
linelength =
tracklength = 53.85 km (23.3 km undersea)
notrack =
gauge =
el = Yes
speed =
hielevation =
lowelevation= |

The Seikan Tunnel (青函トンネル "Seikan Tonneru" or 青函隧道 "Seikan Zuidō") is a 53.85 km (33.49 mile) railway tunnel in Japan, with a 23.3 km (14.5 mile) portion under the seabed. It is the longest undersea tunnel in the world, although the Channel Tunnel between England and France has a longer under-sea portion. It travels beneath the Tsugaru Strait — connecting Aomori Prefecture on the Japanese island of Honshū and the island of Hokkaidō — as part of the Kaikyo Line of Hokkaido Railway Company. Although it is the longest traffic (railway or road) tunnel in the world, faster and cheaper air travel has left the Seikan Tunnel comparatively underused. Its claim to the record will be taken when the Gotthard Base Tunnel, another railroad tunnel, is completed around 2018. It is also the deepest rail tunnel in the world. [http://www.popularmechanics.com/science/extreme_machines/4217338.html?series=23]

History

Connecting the islands of Honshū and Hokkaidō by a land route had been considered since the Taishō period (1912-1925), but serious survey only commenced in 1946, due to the loss of overseas territory at the end of World War II and the need to accommodate returnees. In 1954, five ferries, including the Toya Maru, sank in the Tsugaru Strait during a typhoon, killing 1,430 passengers. The following year the Japanese National Railways (JNR) expedited the tunnel investigation.

Also of concern was the increasing traffic between the two islands. A booming economy saw traffic levels on the JNR-operated Seikan (a contraction of principal cities Aomori and Hakodate) Ferry doubled to 4,040,000 persons/year from 1955 to 1965, and cargo levels rose 1.7 times to 6,240,000 tonnes/year. In 1971, traffic forecasts predicted increasing growth that would 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-capable cross section was selected, with plans to extend the Shinkansen network.

Arduous construction in difficult geological conditions proceeded. 34 workers were killed during construction.cite news|title = Japan Opens Undersea Rail Line|publisher = Associated Press|page = 6B|date = 14 March 1988]

On January 27, 1983, Japanese Prime Minister Yasuhiro Nakasone pressed a switch that set off a blast that completed the pilot tunnel. Similarly on March 10, 1985, Minister of Transport Tokuo Yamashita symbolically holed through the main tunnel.

However, the project's success was questioned - with the 1971 traffic predictions being overestimates. Instead of the traffic rate increasing to 1985, it peaked in 1978 and then proceeded to decrease — 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.cite news|first = Peter |last = Galloway |title = Japan's super tunnel a political nightmare |work = Special to The Globe and Mail |page = 15 |date = 25 February 1981]

The tunnel was opened on March 13, 1988, at a cost of 538.4 billion yen (US$3.6 billion).cite journal| author=Morse, D. | title=Japan Tunnels Under the Ocean | journal=Civil Engineering | month=May | year=1988 | volume=58 | issue = 5 | pages=50–53]

Once the tunnel was completed, all railway transport between Honshū and Hokkaidō used the tunnel. However, for passenger transport, 90% of people use air due to the speed and cost. For example, to travel between Tokyo and Sapporo by train takes more than 10 hours and 30 minutes, with several transfers. By air, the journey is 3 hours and 30 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.However, the Hokutosei overnight train service, which began service after the completion of the Seikan Tunnel, is still popular among travellers. The newer and more luxurious Cassiopeia overnight train service is frequently fully booked.

urveying, construction and geology

Surveying started in 1946. In 1971, 25 years later, construction began. In August 1982, less than 700 m remained to be excavated. First contact between the two sides was in 1983.

The Tsugaru Strait has eastern and western necks, both approximately 20 km across. Initial surveys undertaken in 1946 indicated that the eastern neck was up to 200 m deep with volcanic geology. The western neck had a maximum depth of 140 m and geology consisting mostly of sedimentary rocks of the Neogene period. The western neck was selected, with its conditions considered favourable for tunnelling.cite journal| author=Tsuji, H., Sawada, T. and Takizawa, M. | title=Extraordinary inundation accidents in the Seikan undersea tunnel | journal=Proceedings of the Institution of Civil Engineers, Geotechnical Engineering | year=1996 | volume=119 | issue= 1 | pages=1–14]

Geology of the undersea portion of the tunnel consists of volcanic rock, pyroclastic rock, and sedimentary rock of the late Tertiary era.cite journal| author=Paulson, B. | title=Seikan Undersea Tunnel | journal=American Society of Civil Engineers, Journal of the Construction Division | year=1981 | volume=107 | issue= 3 | pages=509–525] The area is folded into a nearly vertical anticline, 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 (andesite, basalt etc); the Hokkaidō side consists of sedimentary rocks (Tertiary period tuff, mudstone, etc); and the centre portion consists of Kuromatsunai strata (Tertiary period sand-like mudstone).cite journal| author=Kitamura, A. & Takeuchi, Y. | title=Seikan Tunnel | journal=Journal of Construction Engineering and Management | year=1983 | volume=109 | issue= 1 | pages=25–38] Igneous intrusions and faults caused crushing of the rock and complicated the tunnelling procedures.

Initial geological investigation occurred from 1946 to 1963, and involved: drilling the sea-bed, sonic surveys, submarine boring, observations using a mini-submarine, and seismic and magnetic surveys. However, to establish a greater understanding, horizontal pilot boring was undertaken, in both the service and pilot tunnels.

Tunnelling occurred simultaneously from both the northern and southern ends. The dry land portions were tackled with traditional mountain tunnelling techniques, with a single main tunnel. However, for the 23.3 km 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 shafts, at 600 to 1,000 m intervals. The pilot tunnel served as the service tunnel for the 5 km centre portion.

Beneath the Tsugaru Strait, the use of a tunnel boring machine (TBM) was abandoned after less than 2 km due 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".cite journal| author=Ikuma, M. | title=Maintenance of the undersea section of the Seikan Tunnel | journal=Tunnelling and Underground Space Technology | year=2005 | volume=20 | issue= 2 | pages=143–149| doi=10.1016/j.tust.2003.10.001] The amount of inflow has been decreasing with time, although it "increases right after a large earthquake".

tructure

Currently, only narrow gauge track is laid through the twin tunnels, but the Hokkaidō Shinkansen project (which started construction in 2005) will include laying dual-gauge track and linking the tunnel into the Shinkansen network, so Shinkansen trains can traverse the tunnel to Hakodate (scheduled for 2015) and eventually Sapporo. The tunnel has 52 km of continuous welded rail.cite web | title=Seikan Tunnel Museum | work=記念館案内　青函トンネル記念館　公式ホームページ | url=http://seikan-tunnel-museum.com/museum.html | accessdate=2006-05-08]

Two stations are located within the tunnel: Tappi-Kaitei Station and Yoshioka-Kaitei Station. The stations serve as emergency escape points. In the event of a fire or other disaster, both stations provide the equivalent safety of a much shorter tunnel. The effectiveness of the escape shafts located at the emergency stations is enhanced by: exhaust fans to extract smoke; television cameras to route passengers to safety; thermal (infrared) fire alarm systems; and water spray nozzles.

Previously, both the stations contained museums detailing the history and function of the tunnel, and could be visited on special sightseeing tours. Now only Tappi-Kaitei remains as a museum, Yoshioka-Kaitei was demolished on March 16, 2006 to make way for Hokkaidō Shinkansen preparations.cite web | title=March 2006 | work=jrtr.net | url=http://www.jrtr.net/topics/mar2006.html | accessdate=2006-05-24]

The two stations were also the first train stations in the world built under the sea.

ee also

*Channel Tunnel, an undersea railway tunnel connecting Great Britain and France.
*Seikan Tunnel Tappi Shako Line

References

External links

* [http://www.pref.aomori.jp/newline/shinkan/shinkan/newline-e/sin-e08.html Aomori Prefecture Government site about Hokkaidō shinkansen]

LongestTunnel
start = 1988
end =
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