Seikan Tunnel
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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 travels beneath the Tsugaru Strait — connecting Aomori Prefecture on the Japanese island of Honshū and the island of Hokkaido — as part of the Japan Railways Kaikyo Line. Although it is the longest railway tunnel in the world, faster and cheaper air travel has left the Seikan Tunnel comparatively underutilized.
Contents |
[edit] History
Timeline |
|
|---|---|
| April 24, 1946 | Geological surveying commenced |
| September 26, 1954 | Toya Maru sank in the Tsugaru Straight |
| March 23, 1964 | Japan Railway Construction Public Corporation established |
| September 28, 1971 | Main tunnel construction commenced |
| January 27, 1983 | Pilot tunnel holed through |
| March 10, 1985 | Main tunnel holed through |
| March 13, 1988 | Tunnel opened |
| Source:[1] | |
Connecting the islands of Honshū and Hokkaido 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 1430 passengers. The following year the Japanese National Railways (JNR) expedited the tunnel investigation.[1]
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 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, that 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.[1]
Arduous construction in difficult geological conditions proceeded. 34 workers were killed during construction.[2]
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.[1]
However the project's success was questioned. The 1971 traffic predictions were overestimates. Instead of the traffic rate increasing to 1985, it peaked 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.[3]
The tunnel was opened in 13 March 1988, at a cost of 538.4 billion yen (US$3.6 billon).[4]
| Tsugaru Strait traffic data | |||
|---|---|---|---|
| Year | Passengers (persons/yr) |
Freight (T/yr) | Mode |
| 1955 | 2 020 000 | 3 700 000 | Seikan Ferry[1] |
| 1965 | 4 040 000 | 6 240 000 | Seikan Ferry[1] |
| 1970 | 9 360 000 | 8 470 000 | Seikan Ferry[1] |
| 1985 | 9 000 000 † | 17 000 000 | 1971 Forecast[1] |
| 1988 | ~3 100 000 | — | Seikan Tunnel[5] |
| 1999 | ~1 700 000 | — | Seikan Tunnel[5] |
| 2001 | — | >5 000 000 | Seikan Tunnel[5] |
| † This may be a typographical error in the source | |||
Once the tunnel was completed all railway transport between Honshū and Hokkaido utilised the tunnel. However, for passenger transport 90% of people use air; due to 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. Also, deregulation and competition in domestic air travel has brought down prices on the Tokyo-Sapporo route, making rail more expensive in comparison.[5]
[edit] Surveying, 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.[4]
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.[6]
Geology of the undersea portion of the tunnel consists of volcanic rock, pyroclastic rock, and sedimentary rock of the late Tertiary era.[7] The area is folded into a nearly vertical anticline, which meant 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 (ansesite, basalt etc); the Hokkaido side consists of sedimentary rocks (Tertiary period tuff, mudstone, etc); and the centre portions consists of Kuromatsunai strata (Tertiary period sand-like mudstone).[8] Igneous intrusions and faults caused crushing of the rock and complicated the tunnelling procedures.[6]
Initial geological investigation occurred from 1946 to 1963, and involved drilling the sea-bed, sonic surveys, submarine boring, observations using a mini-submarine, seismic and magnetic surveys. However, to establish a greater understanding, horizontal pilot boring was undertaken - in both the service and pilot tunnels.[6]
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.[6] 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 - 1000 m intervals.[8] The pilot tunnel served as the service tunnel for the 5 km centre portion.[6]
Beneath the Tsugaru Strait 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.[7][6] Blasting with dynamite and mechanical picking were the excavation methods.
[edit] Maintenance
A 2002 report by Michitsugu Ikuma described, for the undersea section, that "the tunnel structure appears to remain in a good condition".[9] The amount of inflow has been decreasing with time, although it "increases right after a large earthquake".[9]
[edit] Structure
Currently, only narrow gauge track is laid through the twin tunnels, but the Hokkaido 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.[10]
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 fire or other disaster the stations provide equivalent safety of a much shorter tunnel. The effectiveness of the escape shafts located at the emergency stations is enhanced by exhaust fans to suck up smoke, television cameras to route passengers to safety, thermal (infrared) fire alarm systems and water spray nozzles.[4] 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 Hokkaido Shinkansen preparations.[11] The two stations were the first train stations in the world built under the sea.
The name 青函 (Seikan) is a contraction of the principal cities on the line through the tunnel. The first kanji is from 青森 (Aomori) and the other from 函館 (Hakodate).[7]
[edit] References
- ^ a b c d e f g h Matsuo, S. (1986). "An overview of the Seikan Tunnel Project Under the Ocean". Tunnelling and Underground Space Technology 1 (3/4): 323-331.
- ^ "Japan Opens Undersea Rail Line", Associated Press, 14 March 1988, p. 6B.
- ^ Galloway, Peter. "Japan's super tunnel a political nightmare", Special to The Globe and Mail, 25 February 1981, p. 15.
- ^ a b c Morse, D. (May 1988). "Japan Tunnels Under the Ocean". Civil Engineering 58 (5): 50-53.
- ^ a b c d Takashima, S. (2001). "Railway Operators in Japan 2: Hokkaido (pdf)". Japan Railway and Transport Review 28: 58-67.
- ^ a b c d e f Tsuji, H., Sawada, T. and Takizawa, M. (1996). "Extraordinary inundation accidents in the Seikan undersea tunnel". Proceedings of the Institution of Civil Engineers, Geotechnical Engineering 119 (1): 1-14.
- ^ a b c Paulson, B. (1981). "Seikan Undersea Tunnel". American Society of Civil Engineers, Journal of the Construction Division 107 (3): 509-525.
- ^ a b Kitamura, A. & Takeuchi, Y. (1983). "Seikan Tunnel". Journal of Construction Engineering and Management 109 (1): 25-38.
- ^ a b Ikuma, M. (1983). "Maintenance of the undersea section of the Seikan Tunnel". Tunnelling and Underground Space Technology 20 (2): 143-149.
- ^ Seikan Tunnel Museum. 記念館案内 青函トンネル記念館 公式ホームページ. Retrieved on 2006-05-08.
- ^ March 2006. jrtr.net. Retrieved on 2006-05-24.
[edit] See also
- Channel Tunnel, an undersea railway tunnel slightly shorter than the Seikan Tunnel
