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Underwater tunnel

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An underwater tunnel is a tunnel which is partly or wholly constructed under the sea or a river. They are often used where building a bridge or operating a ferry link is unviable, or to provide competition or relief for existing bridges or ferry links.[1] While short tunnels are often road tunnels which may admit motorized traffic, unmotorized traffic or both, concerns with ventilation lead to the longest tunnels (such as the Channel Tunnel or the Seikan Tunnel) being electrified rail tunnels.

Types of tunnel

Various methods are used to construct underwater tunnels, including an immersed tube and a submerged floating tunnel. The immersed tube method involves steel tube segments that are positioned in a trench in the sea floor and joined together. The trench is then covered and the water pumped from the tunnel.[2] Submerged floating tunnels use the law of buoyancy to remain submerged, with the tunnel attached to the sea bed by columns or tethers, or hung from pontoons on the surface.[3]


Compared with bridges

One such advantage would be that a tunnel would still allow shipping to pass. A low bridge would need an opening or swing bridge to allow shipping to pass, which can cause traffic congestion. Conversely, a higher bridge that does allow shipping may be unsightly and opposed by the public. Higher bridges can also be more expensive than lower ones. Bridges can also be closed due to harsh weather such as high winds.

Tunneling makes excavated soil available that can be used to create new land (see land reclamation). This was done with the rock excavated for the Channel Tunnel, which was used to create Samphire Hoe.

Compared with ferry links

A map of assessed Helsinki–Tallinn Tunnel through the Gulf of Finland as part of the Rail Baltica project

As with bridges, albeit with more chance, ferry links will also be closed during adverse weather. Strong winds or the tidal limits may also affect the workings of a ferry crossing. Travelling through a tunnel is significantly quicker than travelling using a ferry link, shown by the times for travelling through the Channel Tunnel (75–90 minutes for Ferry[4] and 21 minutes on the Eurostar). Ferries offer much lower frequency and capacity[citation needed] and travel times tend to be longer with a ferry than a tunnel. Ferries also usually use fossil fuels emitting greenhouse gases in the process while most railway tunnels are electrified. In the Baltic Sea, one of the busiest areas for passenger ferries in the world, sea ice is a problem, causing seasonal disruption or requiring expensive ice-breaking ships. In the Øresund region the construction of the bridge-tunnel has been cited as enhancing regional integration and giving an economic boom not possible with the previous ferry links. Similar arguments are used by proponents of the Helsinki-Tallinn tunnel in the Talsinki region. There are various issues with the safety of both tunnels and ferries, in the case of tunnels, fire is a particular hazard with several fires having broken out in the Channel Tunnel. On the other hand, the free surface effect is a significant safety risk for RORO ferries as seen in the sinking of MS Estonia. Tunnels which exclude dangerous, combustible freights and the fuel or lithium-ion batteries carried aboard motorcars can significantly reduce fire risk.


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Compared with bridges

Tunnels require far higher costs of security and construction than bridges.[citation needed] This may mean that over short distances bridges may be preferred rather than tunnels (for example Dartford Crossing). As stated earlier, bridges may not allow shipping to pass, so solutions such as the Øresund Bridge have been constructed.

Compared with ferry links

As with bridges, ferry links are far cheaper to construct than tunnels, but not to operate. Also tunnels don't have the flexibility to be deployed over different routes as transport demand changes over time. Without the cost of a new ferry, the route over which a ferry provides transport can easily be changed. However, this flexibility can be a downside for customers who have come to rely on the ferry service only to see it abandoned. Fixed infrastructure such as bridges or tunnels represent a much more concrete commitment to sustained service.

List of notable examples

Name Place Description Length Depth (from surface) Constructed in
Thames Tunnel London, England Thought to be the oldest tunnel under a navigable river, crossing the Thames in London 0.4 km 1825–1843
Mersey Railway Tunnel Liverpool, England The oldest underwater rail tunnel in the world, crossing the Mersey in Liverpool 1.21 km 1881–1886
Severn Tunnel Wales – England One of the oldest underwater rail tunnels in the world 7.01 km 1873–1886
Blackwall Tunnel (western) London, England The oldest underwater vehicular tunnel in the world, crossing the Thames in London 1.35 km 1892–1897
Elbe Tunnel (1911) Hamburg, Germany Pioneering underwater pedestrian and vehicular tunnel, crossing the Elbe River in Hamburg 0.426 km 24 m 1907–1911
Holland Tunnel New York – New Jersey, USA The longest continuous underwater vehicular tunnel in the world when first built, crossing the Hudson River between Manhattan and Jersey City 2.6 km 28.3 m 1920–1927
Detroit–Windsor Tunnel Windsor, CanadaDetroit, USA Connect Ontario, Canada to Michigan, USA. under the Detroit River opened on November 3, 1930 1.57 km 13.7 m 1928–1930
CESC Tunnel Kolkata, India It is the first underwater tunnel of Asia, as well as India. The construction of this tunnel was completed in 1931.[5] This tunnel is used for electric power transmission between Kolkata and Howrah. 0.539 km 33.5 m 1931
Tongyeong Undersea Tunnel Tongyeong, South Korea The first undersea tunnel in Asia, connecting Tongyeong to the Mireukdo island 0.483 km 13.5 m 1932
Queensway Tunnel Liverpool, England The longest vehicular tunnel of any type in the world when first built, crossing the Mersey estuary between Liverpool and Birkenhead 3.24 km 1925–1934
Bankhead Tunnel Mobile, Alabama Carries Hwy. 90 in Mobile, AL. Business District, to Blakely Island. The eastern end has large "flood door" that can be closed to prevent water from the Mobile Bay from flooding the tunnel during hurricanes or tropical storms. Two lanes that only allows[clarification needed] cars and pick up trucks now[clarification needed] to travel through the tunnel 1.033 km 12.2 m 1938–1942
Kanmon Railway Tunnel Kanmon Straits, Japan The first undersea tunnel in Japan, connecting the islands of Honshu and Kyushu. One of three tunnels underneath the Kanmon Straits 3.604 km 1936–1942
Lincoln Tunnel New York, USA Set of road tunnels built in three stages, crossing the Hudson River between Manhattan and New Jersey 2.4 km average 30 m 1934–1957
Kanmon Roadway Tunnel Kanmon Straits, Japan The second of three tunnels under the Kanmon Straits, connecting the islands of Honshu and Kyushu. It was the world's longest undersea road tunnel at the time of its construction and includes a tunnel for pedestrians and cyclists 3.461 km 58 m 1937–1958
Havana Tunnel Havana, Cuba Road tunnel built during the Batista era, crossing the Havana Bay 0.733 km 12 m 1957–1958
George Massey Tunnel Vancouver, Canada The first tunnel in British Columbia to use Immersed Tube technology 0.629 km 23 m 1957–1959
Muskö Tunnel Muskö, Sweden Connecting Muskö island to mainland in Stockholm coastal region 2.9 km 65 m 1959–1964
Sandoyartunnilin Sandoy, Faroe Islands Connecting Sandoy to the main island Eysturoy 10.8 km 155 m 2018–2023
Chesapeake Bay Bridge Tunnel Virginia, USA Connects Virginia Beach with the Eastern Shore of Virginia. Length refers to the tunnel section 1.6 km 1960–1964
Transbay Tube San FranciscoOakland, USA Rail tunnel for Bay Area Rapid Transit. Connects Oakland to San Francisco. It is the longest underwater tunnel in North America 5.8 km 41 m 1965–1969
Cross-Harbour Tunnel Hong Kong A busy road tunnel in Hong Kong 1.86 km 1969–1972
Elbe Tunnel (1975) Hamburg, Germany 8-lane road tunnel crossing the Elbe River in Hamburg 3.3 km 1968–1975
Ahmed Hamdi Tunnel Suez, Egypt Passes under Suez Canal connecting the Asian Sinai Peninsula to the town of Suez on the African mainland 7 tunnels (2 rail, 4 road, 1 other) under New Suez Canal 1.63 km 1979–1981
Vardø Tunnel Vardø, Norway Connecting the small island community of Vardø in northern Norway to the mainland 2.9 km 88 m 1979–1982
Kanonersky Tunnel Saint-Petersburg, Russia Connects Kanonersky Island to the Kirovsky District of Saint-Petersburg through Neva Bay 0.927 km 1975–1983
Seikan Tunnel Seikan, Japan The Seikan Tunnel is the world's longest tunnel with an undersea segment 53.8 km 240 m 1971–1988
Flekkerøy Tunnel Flekkerøy, Norway Connecting the island community of Flekkerøy in southern Norway to the mainland 2.3 km 101 m 1986–1989
Sydney Harbour Tunnel Sydney, Australia 2.8 km 1988–1992
Channel Tunnel England – France The world's longest undersea portion railway tunnel (37.9 km underwater length) 50.4 km 1988–1994
Hitra Tunnel Trøndelag, Norway The deepest in the world at the time of construction 5.6 km 264 m 1992–1994
Tokyo Bay Aqua-Line Tokyo, Japan The world's 2nd longest undersea portion road tunnel 9.6 km 1988–1997
Massachusetts Bay Outfall Boston, USA The outfall for the Deer Island Treatment Plant. It discharges treated sewage into Massachusetts Bay instead of into the shallower waters of Boston Harbor.[6] Tunnel diameter 24 feet 3 inches (7.39 m) 15.3 km 120 m 1992–1998
North Cape Tunnel Magerøya, Norway Under Magerøysundet, a strait between the Norwegian mainland and the large island of Magerøya and the North Cape, Norway 6.8 km 212 m 1993–1999
Bømlafjord Tunnel FøynoSveio, Norway The deepest point of the International E-road network. Connects Stord municipality to the Norwegian mainland 7.8 km 260.4 m 1997–2000
Eiksund Tunnel Møre og Romsdal, Norway The world's second deepest undersea road tunnel (before 2019 world's deepest) 7.7 km 287 m 2003–2008
Xiang'an Tunnel Xiamen, China 6.05 km 70 m 2005–2010
Busan–Geoje Fixed Link Busan – Geoje, South Korea 3.7 km 48 m 2008–2010
Qingdao Jiaozhou Bay Tunnel HangdaoQingdao, China 7.808 km 84.2 m 2006–2011
Marmaray Istanbul (Bosphorus strait), Turkey Rail tunnel connecting Asia and Europe. Length refers to the undersea section 1.39 km 2004–2013
Marina Coastal Expressway Singapore Singapore's first undersea tunnel 5 km 2008–2013
Port of Miami Tunnel Miami, USA 2.1 km 2010–2014
Eurasia Tunnel Istanbul (Bosphorus strait), Turkey Road tunnel connecting Asia and Europe in Istanbul 5.4 km 106 m 2011–2016
Hong Kong–Zhuhai–Macau Bridge Hong Kong – Macau, China 55 km-long sea crossing between Hong Kong, Macau and Zhuhai, China. Length refers to the tunnel section 6.7 km 2009–2018
Riachuelo Lot 3 Tunnel Buenos Aires, Argentina Outfall tunnel of the Riachuelo System - 2nd world's longest outfall undersea tunnel and 4th world's longest undersea tunnel excavated with TBM 12 km 48 m 2017–2019
The Ryfast Tunnel StavangerRyfylke, Norway The longest and deepest undersea tunnel for cars, from Stavanger to Ryfylke 14.3 km 293 m 2013–2020
Eysturoyartunnilin Faroe Islands Sea crossing between Hvítanes, Strendur and Saltnes, under the Tangafjørður strait. Includes an underwater roundabout[7][8] 11.24 km (overall length)[9] 187 m[10] 2017–2020
Tuen Mun–Chek Lap Kok Link Hong Kong Sea crossing between Tung Chung and Tuen Mun, Hong Kong. Length refers to the tunnel section. 5 km 2011–2020
Boryeong Undersea Tunnel Boryeong, South Korea 5th longest undersea section in the world, connects Boryeong with Wonsan Island 6.927 km 80 m 2012-2021
Musaimeer Outfall Tunnel Doha, Qatar Diameter 3.7 m 10.2 km 40 m 2017-2021
Haicang Tunnel Xiamen, China 6.293 km 73.6 m 2016–2021
East West Metro Tunnel Kolkata, India The biggest and the first underwater river railway tunnel in India. It is a metro railway tunnel connecting Kolkata to Howrah.[11] [12] 0.520 km 30 m 2021
Bangabandhu Sheikh Mujibur Rahman Tunnel Chittagong, Bangladesh First under-river road tunnel in South Asia 3.32 km 18 - 31 m 2019–2022
Hvalfjörður Tunnel Capital Region, Iceland Road tunnel serving as a link between Reykjavik and western portions of the country. 5.77 km 165 m 1996-1998
Great Belt Fixed Link Sjælland, Sprogø, Denmark Rail tunnel serving as a link between Sjælland and Sprogø. 8 km 80 m 1988-1995




See also


  1. ^ Sullivan, Walter. Progress In Technology Revives Interest In Great Tunnels, New York Times, June 24, 1986. Retrieved 15 August 2010.
  2. ^ Gursoy, Ahmet (1996), Bickel, John O.; Kuesel, Thomas R.; King, Elwyn H. (eds.), "Immersed Tube Tunnels", Tunnel Engineering Handbook, Boston, MA: Springer US, pp. 268–297, doi:10.1007/978-1-4613-0449-4_14, ISBN 978-1-4613-0449-4, retrieved 2022-02-17
  3. ^ Ingerslev, Christian (2010-01-01). "Immersed and floating tunnels". Procedia Engineering. ISAB-2010. 4: 51–59. doi:10.1016/j.proeng.2010.08.007. ISSN 1877-7058.
  4. ^ Dover–Calais Ferry Times, website.
  5. ^ "Kolkata Metro: 87 years on, boring re-creates CESC feat | Kolkata News - Times of India". The Times of India. TNN. Apr 18, 2017. Retrieved 2022-09-29.
  6. ^ "The Massachusetts Bay Outfall". Massachusetts Water Resources Authority. Retrieved 29 March 2021.
  7. ^ "Eysturoyartunnilin verður liðugur í 2019". Archived from the original on June 13, 2018.
  8. ^ "Faroe Islands: Inside the undersea tunnel network". BBC News. 4 December 2020. Retrieved 4 January 2021.
  9. ^ "The Eysturoy tunnel". Eystur- og Sandoyatunlar.
  10. ^ "Eysturoy tunnel built by NCC opened in Faroe Islands". NCC. 19 December 2020.
  11. ^ "Kolkata Metro's TBM S639 Crosses Halfway Mark Under Hooghly". The Metro Rail Guy. 2017-05-05. Retrieved 2023-02-14.
  12. ^ "Watch: PM Modi takes Kolkata Metro ride with students in India's 1st underwater tunnel". Hindustan Times. 2024-03-06. Retrieved 2024-03-06.
  13. ^ "Undersea Road Tunnel Salamina island - Perama". Retrieved 2020-05-13.
  14. ^ Καραγιάννης, Νίκος (2020-05-12). "Design for Salamina island undersea road tunnel, finalized". (in Greek). Retrieved 2020-05-13.
  15. ^ a b "India to build sea bridge, tunnel to connect Sri Lanka at a cost of Rs 24,000 crore". The Economic Times. 16 December 2015.
  16. ^ "我市全国人大代表返连努力创造属于新时代的光辉业绩_大连新闻_时政经济_大连天健网". Archived from the original on July 28, 2018.
This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed.Find sources: "Underwater tunnel" – news · newspapers · books · scholar · JSTOR (August 2010) (Learn how and when to remove this message)
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Underwater tunnel
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