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]

Advantages

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.

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 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.

Disadvantages

Compared with bridges

Tunnels require far higher costs of security and construction than bridges. 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.

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

NamePlaceDescriptionLengthDepth (from surface)Constructed in
Thames Tunnel London, EnglandThought to be the oldest tunnel under a navigable river, crossing the Thames in London0.4 km1825–1843
Mersey Railway Tunnel Liverpool, EnglandThe oldest underwater rail tunnel in the world, crossing the Mersey in Liverpool1.21 km1881–1886
Severn Tunnel Wales – EnglandOne of the oldest underwater rail tunnels in the world7.01 km1873–1886
Blackwall Tunnel (western) London, EnglandThe oldest underwater vehicular tunnel in the world, crossing the Thames in London1.35 km1892–1897
Elbe Tunnel (1911) Hamburg, GermanyPioneering underwater pedestrian and vehicular tunnel, crossing the Elbe River in Hamburg0.426 km24 m1907–1911
Holland Tunnel New York – New Jersey, USAThe longest continuous underwater vehicular tunnel in the world when first built, crossing the Hudson River between Manhattan and Jersey City2.6 km28.3 m1920–1927
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 KoreaThe first undersea tunnel in Asia, connecting Tongyeong to the Mireukdo island0.483 km13.5 m1932
Queensway Tunnel Liverpool, EnglandThe longest vehicular tunnel of any type in the world when first built, crossing the Mersey estuary between Liverpool and Birkenhead3.24 km1925–1934
Bankhead Tunnel Mobile, AlabamaCarries 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 cars and pick up trucks now to travel through the tunnel1.033 km12.2 m1938–1942
Kanmon Railway Tunnel Kanmon Straits, JapanThe first undersea tunnel in Japan, connecting the islands of Honshu and Kyushu. One of three tunnels underneath the Kanmon Straits3.604 km1936–1942
Lincoln Tunnel New York, USASet of road tunnels built in three stages, crossing the Hudson River between Manhattan and New Jersey2.4 km average30 m1934–1957
Kanmon Roadway Tunnel Kanmon Straits, JapanThe 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 cyclists3.461 km58 m1937–1958
Havana Tunnel Havana, CubaRoad tunnel built during the Batista era, crossing the Havana Bay0.733 km12 m1957–1958
George Massey Tunnel Vancouver, CanadaThe first tunnel in British Columbia to use Immersed Tube technology0.629 km23 m1957–1959
Muskö Tunnel Muskö, SwedenConnecting Muskö island to mainland in Stockholm coastal region2.9 km65 m1959–1964
Sandoyartunnilin Sandoy, Faroe IslandsConnecting Sandoy to the main island Eysturoy10.8 km155 m2018–2023
Chesapeake Bay Bridge Tunnel Virginia, USAConnects Virginia Beach with the Eastern Shore of Virginia. Length refers to the tunnel section1.6 km1960–1964
Transbay Tube San FranciscoOakland, USARail tunnel for Bay Area Rapid Transit. Connects Oakland to San Francisco. It is the longest underwater tunnel in North America5.8 km41 m1965–1969
Cross-Harbour Tunnel Hong KongA busy road tunnel in Hong Kong1.86 km1969–1972
Elbe Tunnel (1975) Hamburg, Germany8-lane road tunnel crossing the Elbe River in Hamburg3.3 km1968–1975
Ahmed Hamdi Tunnel Suez, EgyptPasses 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 Canal1.63 km1979–1981
Vardø Tunnel Vardo, NorwayConnecting the small island community of Vardø in northern Norway to the mainland2.9 km88 m1979–1982
Kanonersky Tunnel Saint-Petersburg, RussiaConnects Kanonersky Island to the Kirovsky District of Saint-Petersburg through Neva Bay0.927 km1975–1983
Seikan Tunnel Seikan, JapanThe Seikan Tunnel is the world's longest tunnel with an undersea segment53.8 km240 m1971–1988
Flekkerøy Tunnel Flekkerøy, NorwayConnecting the island community of Flekkerøy in southern Norway to the mainland2.3 km101 m1986–1989
Sydney Harbour Tunnel Sydney, Australia2.8 km1988–1992
Channel Tunnel England – FranceThe world's longest undersea portion railway tunnel (37.9 km underwater length)50.4 km1988–1994
Hitra Tunnel Trøndelag, NorwayThe deepest in the world at the time of construction5.6 km264 m1992–1994
Tokyo Bay Aqua-Line Tokyo, JapanThe world's 2nd longest undersea portion road tunnel9.6 km1988–1997
Massachusetts Bay Outfall Boston, USAThe 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)0.115 km 1992–1998
North Cape Tunnel Magerøya, NorwayUnder Magerøysundet, a strait between the Norwegian mainland and the large island of Magerøya and the North Cape, Norway6.8 km212 m1993–1999
Bømlafjord Tunnel FøynoSveio, NorwayThe deepest point of the International E-road network. Connects Stord municipality to the Norwegian mainland 7.8 km260.4 m1997–2000
Eiksund Tunnel Møre og Romsdal, NorwayThe world's second deepest undersea road tunnel (before 2019 world's deepest)7.7 km287 m2003–2008
Xiang'an Tunnel Xiamen, China6.05 km70 m2005–2010
Busan–Geoje Fixed Link Busan – Geoje, South Korea3.7 km48 m2008–2010
Qingdao Jiaozhou Bay Tunnel HangdaoQingdao, China7.808 km84.2 m2006–2011
Marmaray Istanbul (Bosphorus strait), TurkeyRail tunnel connecting Asia and Europe. Length refers to the undersea section1.39 km2004–2013
Marina Coastal Expressway SingaporeSingapore's first undersea tunnel5 km2008–2013
Port of Miami Tunnel Miami, USA2.1 km2010–2014
Eurasia Tunnel Istanbul (Bosphorus strait), TurkeyRoad tunnel connecting Asia and Europe in Istanbul5.4 km106 m2011–2016
Hong Kong–Zhuhai–Macau Bridge Hong Kong – Macau, China55 km-long sea crossing between Hong Kong, Macau and Zhuhai, China. Length refers to the tunnel section6.7 km2009–2018
Riachuelo Lot 3 Tunnel Buenos Aires, ArgentinaOutfall tunnel of the Riachuelo System - 2nd world's longest outfall undersea tunnel and 4th world's longest undersea tunnel excavated with TBM12 km48 m2017–2019
The Ryfast Tunnel StavangerRyfylke, NorwayThe longest and deepest undersea tunnel for cars, from Stavanger to Ryfylke14.3 km293 m2013–2020
Eysturoyartunnilin Faroe IslandsSea 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 KongSea crossing between Tung Chung and Tuen Mun, Hong Kong. Length refers to the tunnel section.5 km2011–2020
Boryeong Undersea Tunnel Boryeong, South Korea5th longest undersea section in the world, connects Boryeong with Wonsan Island6.927 km80 m2012-2021
Musaimeer Outfall Tunnel Doha, QatarDiameter 3.7 m 10.2 km40 m2017-2021
Haicang Tunnel Xiamen, China6.293 km73.6 m2016–2021
East West Metro Tunnel Kolkata, IndiaThe biggest underwater river railway tunnel in India. It is a metro railway tunnel connecting Kolkata to Howrah.[11]0.520 km30 m2021
Bangabandhu Sheikh Mujibur Rahman Tunnel Chittagong, BangladeshFirst under-river road tunnel in South Asia3.32 km18 - 31 m2019–2022
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

Proposed

Road

Rail

See also

References

  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, poferries.com 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". sjovarkommuna.fo. 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. "Undersea Road Tunnel Salamina island - Perama". ec.europa.eu. Retrieved 2020-05-13.
  13. Καραγιάννης, Νίκος (2020-05-12). "Design for Salamina island undersea road tunnel, finalized". Ypodomes.com (in Greek). Retrieved 2020-05-13.
  14. 1 2 "India to build sea bridge, tunnel to connect Sri Lanka at a cost of Rs 24,000 crore". The Economic Times. 16 December 2015.
  15. "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". dalian.runsky.com. Archived from the original on July 28, 2018.
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