Seikan tunnel

The Seikan Tunnel (青函トンネル Seikan Tonneru, or 青函隧道 Seikan Zuidō) is the second longest railway tunnel in the world, only surpassed by the Gotthard tunnel and the longest tunnel with an underwater section (the Eurotunnel is shorter, but its underwater segment is longer). It is 53 km long, with a 23.3 km portion under the seabed. Opened on March 13, 1988, it links the islands of Honshū and Hokkaidō in Japan. It is 100 m below the seabed and 240 m below sea level. It crosses the Tsugaru Strait—connecting Aomori Prefecture on the island of Honshū and the island of Hokkaido—as part of the Japan Railways Kaikyo Line.

The name 青函 (Seikan) comes from the combination of the on'yomi readings of the first few characters of Aomori (青森), the nearest major city on the Honshu side of the strait, and Hakodate (函館), the nearest major city on the Hokkaido side.

It took 25 years to build, and although it is the second longest rail tunnel in the world, air travel is faster and cheaper, which has meant that the Seikan Tunnel is relatively underused.

The tunnel originally had a track gauge of 1,067mm and was adapted by third rail to 1,435mm.

History

Tunnel section. (1) Main tunnel, (2) service tunnel, (3) Pilot tunnel, (4) Connection gallery

Since the Taishō Era (1912-1925) it was studied to connect the islands of Honshū and Hokkaido by land route, but serious explorations began only in 1946, following the loss of overseas territories after Japan's surrender to Japan. end of World War II and the need to accommodate the repatriates who returned to Japan. In 1954 five ferries, including the Toya Maru, sank at sea during a typhoon, killing &&&&&& &&&&&01430.&&&&&01430 passengers. The following year, the Japan National Railway Company (JNR) began exploration for its construction.

The increase in travel between the islands also had an influence. A growing economy lifted traffic levels on the JNR-operated Seikan Ferry, doubling at &&&&&&&&04040000.&&&&&04,040,000 people a year from 1905 to 1965, and charge levels grew 1.7 times to &&& &&&&&06240000.&&&&&06,240,000 tons per year. In 1971, traffic information predicted an increase that would exceed the capacity of the ferry port limited by geographical conditions. In September 1971 the decision was made. The arduous and dangerous construction in difficult conditions caused the death of 34 workers.

On January 27, 1983, Japanese Prime Minister Yasuhiro Nakasone pushed the button that caused the explosion to complete the pilot tunnel. Also on March 10, 1985, the Minister of Transportation Tokuo Yamashita symbolically drilled the main tunnel.

However, the success of the project was questioned. Traffic predictions in 1971 were overestimated. Although it increased in 1985, it peaked in 1978 and then declined — attributed to the downturn in the economy since the 1973 oil crisis and advances in air and sea transportation.

The tunnel was opened on March 13, 1988, at a cost of 538.4 billion yen (US$3.6 billion).

Once the tunnel was completed, all rail transport between Honshū and Hokkaido used the tunnel. However, 90% of passenger transport between Honshu and Hokkaido is by air because of the speed and cost of travel. For example, traveling between Tokyo and Sapporo by train takes around eight hours while by air, the journey takes approximately ninety minutes. Since March 26, 2016, Shinkansen trains use the tunnel thanks to the inauguration of the line between Shin-Aomori and Shin-Hakodate-Hokuto stations. The Hokkaidō Shinkansen, which currently runs as far as Shin-Hakodate, is expected to decrease the train travel time of the Tokyo-Sapporo section to less than 4 hours when it opens in early 2031, making the land route competitive with the air route.

Timeline of construction

• April 24, 1946: the geological study begins.
• 26 September 1954: the ferry train Tōya Maru It sinks into the strait of Tsugaru.
• March 23, 1964: Japan's Public Railway Construction Corporation is established.
• September 28, 1971: The construction of the main tunnel begins.
• January 27, 1983: advance of the pilot tunnel.
• 10 March 1985: advance of the main tunnel.
• 13 March 1988: The tunnel opens.
• March 26, 2016: Shinkansen services begin to operate through the tunnel, stop the regular services of narrow-way passengers through the tunnel.

Prospecting, construction and geology

Tunnel profile. (2) and (3) are submarine stations.

Prospecting began in 1946. In 1971, 25 years later, the works began. In August 1982, less than 700 meters remained to be excavated. The first contact between the two sides took place in 1983.

The Tsugaru Strait has western and eastern necks, both 20 km long. Surveys started in 1946 indicated that the eastern neck, more than 200 m deep, was of volcanic geology. The western neck, with a maximum of 140 m, has sedimentary rocks from the Neogene period. The western neck was ultimately selected because its conditions were optimal for a tunnel.

The geology of the subsea portion of the tunnel is Late Tertiary volcanic rock, pyroclastic rock, and sedimentary rock. The area is on an anticlinal vertical slope, meaning that the most recent rock is in the center of the layer. It can be roughly divided into three parts: the Honshū side consisting of volcanic rocks (andesite, basalt, etc.); the Hokkaido side with sedimentary rocks (Tertiary period) and the central portion consisting of Kuromatsunai strata (sand-like Tertiary period). Igneous intrusions and faulting caused the rock to break and complicated the works.

Initial geological investigations were conducted between 1946 and 1963, and involved seabed drilling, sonic testing, underwater observations (with mini-submarines), seismic and magnetic testing.

The tunnel was drilled simultaneously from the north and south sides. Construction was carried out on the land portion with traditional mountain tunneling techniques, with only one main tunnel. But, for the 23.3 km of the undersea portion, three tunnels with increasing diameters were dug, respectively.: an initial pilot tunnel, a service tunnel and finally the main tunnel. The service tunnel is linked to the main one by a series of connecting galleries at intervals of 600 - 1000 m. The pilot tunnel serves the service tunnel for the 5 km of the central portion.

Near the Tsugaru Strait, a drilling rig (TBM) was taken out of use after less than 2 km due to the variable density of the rock at the site, making it difficult to access for drilling. Methods for excavation were drilling with dynamite and manual.

Maintenance

A 2002 report by Michitsugu Ikuma described, for the undersea section, that "the tunnel structure is apparently in good condition". risk during an earthquake." As of March 2018, at age 30, maintenance costs amounted to 30 billion yen or 286 million US dollars since 1999. Plans are to increase speed and provide mobile communication throughout the clue.

Structure

Train approaching Tappi-Kaitei station.

Initially, only narrow gauge (1067 mm) passed through the tunnels, but the Hokkaido Shinkansen (which began construction in 2005 and whose first train passed through the tunnel on March 26, 2016) included the laying of three-lane tracks (narrow and standard 1435mm) and connected the tunnel to the Shinkansen network, so Shinkansen trains can go through the tunnel to Hakodate and in the future to Sapporo. The tunnel has 52 km of continuous seamless rails. The maximum speed in the tunnel is 140 km/h on the normal track and 110 km/h on the narrow gauge.

Two stations are connected to the tunnel: Tappi-Kaitei and Yoshioka-Kaitei. The stations serve as escape points for emergencies. In the event of fire or other disasters, the stations provide security equivalent to another shorter tunnel. The effectiveness of escape exits located at emergency stations is increased by exit fans that absorb smoke, television cameras that guide passengers to the exit, thermal (infrared) alarms, and water launchers. In addition, both stations They have museums detailing the tunnel's history and function, and can be visited on special tours. Only now Tappi-Kaitei remains as a museum, Yoshioka-Kaitei was demolished on March 16, 2006 to make way for preparations for the Hokkaido Shinkansen. The two stations were the world's first to be built under the sea.