TheSeikan Tunnel (Japanese:青函トンネル,Seikan Tonneru or青函隧道,Seikan Zuidō) is a 53.85-kilometre (33.5-mile)dual-gauge railway tunnel in Japan, with a 23.3-kilometre (14.5-mile) segment running beneath the seabed of theTsugaru Strait, which separatesAomori Prefecture onHonshu,Japan's main island, from the northern island ofHokkaido. The tunnel's track level lies approximately 100 metres (330 ft) below the seabed and 240 metres (790 ft) below sea level.[2] Following several decades of planning and construction, the tunnel opened on 13 March 1988.
The tunnel plan was handed over to theMinistry of Railways in 1946, with preliminary geological surveys and feasibility studies beginning on 24 April of that year[7] induced by the loss of overseas territory at the end ofWorld War II and the need to accommodate returnees. In 1954, five ferries, including theTōya Maru, sank in the Tsugaru Strait during a typhoon, killing 1,430 passengers.[8] The following year,Japanese National Railways (JNR) expedited the tunnel feasibility study.[8] Also of concern was increasing traffic between the two islands; a booming economy saw traffic levels on the JNR-operated Seikan Ferry double to 4,040,000 passengers a year from 1955 to 1965, and cargo levels rose 1.7 times to 6,240,000 tonnes a 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.[8]
On 22 March 1964, the Japan Railway Construction Public Corporation was established, and excavation work began that year.[8][9] In September 1971, the decision was made to commence work on the tunnel. Drilling began in 1972 from both sides—Hamana on the northern tip of Honshu, and Yunosato in Hokkaido.[7] To avoid danger from earthquakes, the tunnel goes through dense volcanic rock.[7] The tunnel was constructed using conventional construction methods, includingblasting with theNew Austrian tunneling method (NATM) andtunnel boring machines (TBMs). AShinkansen-capable cross section was selected with plans to extend the Shinkansen network.[8] Arduous construction in difficult geological conditions proceeded despite multiple challenges including drilling difficulties, tunnel floodings, and the1973 oil crisis, which delayed completion of the tunnel.[7] 34 workers were killed during construction.[10][11][12]
The necessity for the project was questioned at times during construction, as ferry traffic predictions made in 1971 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 1973 oil crisis and to advances made in air transport facilities and longer-range sea transport.[13] Construction had begun during the heyday of the Seikan ferry route, but the ferry became mostly supplanted by air travel. On the freight side, due to the deterioration of labour-management relations at JNR at the time, including frequentstrikes and legal compliance struggles, freight rail transportation stagnated and lost market share to ferries and coastal shipping.
By mid-1982, the tunnel had only 1,000 metres (3,300 ft) to complete.[14] On 27 January 1983, Japanese Prime MinisterYasuhiro Nakasone pressed a switch that set off a blast that completed thepilot tunnel.[8] Following this, on 10 March 1985, Minister of TransportTokuo Yamashita symbolically bored through the main tunnel[8][15] by detonating a dynamite charge on the last few meters of the earth.[15]
The tunnel was opened on 13 March 1988,[12] 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).[16] Construction of the tunnel itself was projected to cost ¥538.4 billion, but actually cost ¥745.5 billion, and construction of the line running through the tunnel was projected to cost ¥689 billion, but ended up costing ¥900 billion. To commemorate the opening, acommemorative 500 yen coin depicting the tunnel was issued by theJapan Mint in 1988.[17]
Once the tunnel was completed, it became used by all railway transport between Honshu and Hokkaido,[18] particularly conventional express trains,[12] with all passenger services combined making up to 21 round trips daily (up to 50 round trips if freight trains are included). Similarly, the commuter ferry service between the two islands run by JNR[9][19] was also discontinued.[9] However, 90% of passenger transport is still by plane due to travel time and cost. For example, to travel betweenTokyo Station andShin-Sapporo Station by train takes eight hours, with transfer from Shinkansen to narrow-gauge express train atShin-Hakodate-Hokuto Station. By air, the journey is 1 hour and 45 minutes, or 3 hours and 30 minutes including airport access times. Deregulation and competition in Japanese domestic air travel has brought down prices for the Tokyo-Sapporo route, making rail travel more expensive in comparison.[18]
TheHokutosei overnight train service began after the completion of the Seikan Tunnel;[20] a later and more luxuriousCassiopeia overnight train service was often fully booked. Both were discontinued following the commencement ofHokkaido Shinkansen services in March 2016, with freight trains being the only regular service utilising the narrow-gauge line since then.[21][22][23] Research was conducted into a "Train on Train"piggybacking system to increase the speed of narrow-gauge freight trains, which currently prevent Shinkansen trains from running at full speed.[24]
As of March 2019, Shinkansen trains operate through the tunnel, connecting Tokyo Station andShin-Hakodate-Hokuto Station in 3 hours and 58 minutes. Their maximum speed is 160 km/h (100 mph) within the tunnel, 260 km/h (160 mph) outside it, and 320 km/h (200 mph) south ofMorioka.[25] It was expected that by 2018, one daily service would be run at 260 km/h (160 mph) through the tunnel. The final stage is proposed to open toSapporo Station in 2038 and is expected to shorten the Tokyo-Sapporo rail journey to five hours.
Typical tunnel cross section.(1) Main tunnel,(2) service tunnel,(3) pilot tunnel,(4) connecting galleryProfile diagram of the undersea tunnel section
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.[27] TheTsugaru Strait has eastern and western necks, both approximately 20 km (12 mi) across. Initial surveys undertaken in 1946 indicated that the eastern neck was up to 200 metres (656 feet) deep with volcanic geology. The western neck had a maximum depth of 140 metres (459 feet) and geology consisting mostly of sedimentary rocks of theNeogene period. The western neck was selected, with its conditions considered favourable for tunnelling.[28]
The geology of the undersea portion of the tunnel consists of volcanic rock,pyroclastic rock, and sedimentary rock of the Neogene period.[29] The area is folded into a nearly verticalsyncline, which means that the youngest rock is in the centre of the strait and encountered last. Divided roughly into thirds, the Honshu side consists of volcanic rocks (notably andesite and basalt); the Hokkaido side consists of sedimentary rocks (notablyTertiary periodtuff andmudstone); and the centre portion consists ofKuromatsunaistrata (Tertiary period sand-like mudstone).[30] Igneousintrusions and faults caused crushing of the rock and complicated the tunnelling procedures.[28]
Initial geological investigation occurred from 1946 to 1963, which involved seabed drilling,sonic surveys, submarine boring, observations using a mini-submarine, and seismic and magnetic surveys. To establish a greater understanding, a horizontal pilot bore was undertaken along the line of the service and main tunnels.[28] Tunnelling occurred simultaneously from the northern and southern ends. The dry land portions were tackled with traditional mountain tunnelling techniques, with a single main tunnel.[28] However, for the 23.3-kilometre (14.5 mi) 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 connectingdrifts, at 600–1,000-metre (2,000–3,300 ft) intervals.[30] The pilot tunnel serves as the service tunnel for the central five-kilometre portion.[28] Beneath the Tsugaru Strait, the use of atunnel boring machine (TBM) was abandoned after less than 2 kilometres (1.2 miles), owing to the variable nature of the rock and difficulty in accessing the face for advanced grouting.[29][28] Blasting with dynamite and mechanical picking were then used to excavate.
Initially, only1,067 mm (3 ft 6 in)narrow-gauge track was laid through the tunnel, but in 2005 theHokkaido Shinkansen project started construction which included layingdual gauge track (providingstandard gauge track capability) and extending theShinkansen network through the tunnel. Shinkansen services toHakodate commenced in March 2016, and are proposed to be extended toSapporo by 2038. The tunnel has 52 km (32 mi) ofcontinuous welded rail.[31]
Two stations used to be within the tunnel—Tappi-Kaitei Station andYoshioka-Kaitei Station. The two were the first railway stations in the world built under the sea.[32][33] Both closed with the construction of the Hokkaido Shinkansen, but continue to 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.[27] 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.[34]
Entrance to the tunnel from Honshu side; note the dual-gauge tracks
A 2002 report by Michitsugu Ikuma described, for the undersea section, that "the tunnel structure appears to remain in a good condition."[35] The amount of inflow has decreased with time, although it "increases right after a large earthquake".[35] In March 2018 at 30 years of age, maintenance costs amounted to ¥30 billion (US$286 million) since 1999. Plans are to increase travel speeds and provide mobile communication along the full track.[36]
^"Wer hat die grösste Röhre?" [Who has the longest tube?].Tages-Anzeiger (graphical animation) (in German). Zurich, Switzerland. 14 April 2016.Archived from the original on 29 April 2016. Retrieved11 May 2016.
^abcdefghijkMatsuo, S. (1986). "An overview of the Seikan Tunnel Project Under the Ocean".Tunnelling and Underground Space Technology.1 (3–4):323–331.doi:10.1016/0886-7798(86)90015-5.
^"青函トンネル開通記念500円白銅貨幣" [Seikan Tunnel opening commemoration 500 Yen White Copper Coin].Japan Mint (in Japanese).Archived from the original on 23 December 2019. Retrieved29 April 2020.
^寝台特急〈北斗星〉ラストラン [Last run ofHokutosei sleeping car limited express].RM News (in Japanese). Japan: Neko Publishing Co. Ltd. 24 August 2015. Archived fromthe original on 23 August 2017. Retrieved2 September 2015.
^寝台特急"カシオペア"運転終了 ["Cassiopeia" sleeper services end].Japan Railfan Magazine Online (in Japanese). Japan: Koyusha Co., Ltd. 21 March 2016.Archived from the original on 22 March 2016. Retrieved22 March 2016.
^独自の研究開発 人と物流 高速化に活路 [Own R&D leading to increased speed].Hokkaido Shimbun (in Japanese). Japan: The Hokkaido Shimbun Press. 20 December 2008. Archived fromthe original on 18 February 2013. Retrieved30 September 2009.
^"東京―新函館４時間10分 北海道新幹線、16年春開業".Nihon Keizai Shimbun (in Japanese). 16 April 2014.Archived from the original on 26 December 2017. Retrieved16 April 2014.
^"国土交通省鉄道輸送統計年報（平成19年度）".Ministry of Land, Infrastructure, and Transportation (in Japanese). Archived fromthe original on 14 May 2011. Retrieved12 March 2018.
^abMorse, D. (May 1988). "Japan Tunnels Under the Ocean".Civil Engineering.58 (5):50–53.
^abcdefTsuji, H.; Sawada, T.; Takizawa, M. (1996). "Extraordinary inundation accidents in the Seikan undersea tunnel".Proceedings of the Institution of Civil Engineers - Geotechnical Engineering.119 (1):1–14.doi:10.1680/igeng.1996.28131.
^abPaulson, B. (1981). "Seikan Undersea Tunnel".Journal of the Construction Division.107 (3):509–525.doi:10.1061/JCCEAZ.0000983.
