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.[Sullivan, Walter. Progress In Technology Revives Interest In Great Tunnels, New York Times, June 24, 1986. Retrieved 15 August 2010.] 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 .
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.
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.
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, and should it collapse, it may block shipping. 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
As with bridges, albeit with more chance, ferry links may be closed by adverse weather (strong winds) or tides. Travelling through a tunnel is significantly quicker than travelling using a ferry link, as shown by the times for travelling through the
Channel Tunnel (75–90 minutes for ferry
[ Dover–Calais Ferry Times , poferries.com website.] and 21 minutes on the
Eurostar). Ferries also usually use
fossil fuels emitting
greenhouse gases 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.
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
|
|
| Thames Tunnel | 1825–1843 |
| Mersey Tunnel | 1881–1886 |
| Severn Tunnel | 1873–1886 |
| Blackwall Tunnel (western) | 1892–1897 |
| Elbe Tunnel (1911) | 1907–1911 |
| Holland Tunnel | 1920–1927 |
| Detroit–Windsor Tunnel | Windsor, Canada – Detroit | 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. | 0.539 km | 33.5 m | 1931 |
| Tongyeong Undersea Tunnel | 1932 |
| Queensway Tunnel | 1925–1934 |
| Bankhead Tunnel | 1938–1942 |
| Kanmon Railway Tunnel | 1936–1942 |
| Lincoln Tunnel | 1934–1957 |
| Kanmon Roadway Tunnel | 1937–1958 |
| Havana Tunnel | 1957–1958 |
| George Massey Tunnel | 1957–1959 |
| Muskö Tunnel | 1959–1964 |
| Sandoyartunnilin | 2018–2023 |
| Chesapeake Bay Bridge Tunnel | 1960–1964 |
| Transbay Tube | 1965–1969 |
| Cross-Harbour Tunnel | 1969–1972 |
| Elbe Tunnel (1975) | 1968–1975 |
| Ahmed Hamdi Tunnel | 1979–1981 |
| Vardø Tunnel | 1979–1982 |
| Kanonersky Tunnel | 1975–1983 |
| Seikan Tunnel | 1971–1988 |
| Flekkerøy Tunnel | 1986–1989 |
| Sydney Harbour Tunnel | 1988–1992 |
| Channel Tunnel | 1988–1994 |
| Hitra Tunnel | 1992–1994 |
| Tokyo Bay Aqua-Line | 1988–1997 |
| Massachusetts Bay Outfall | 120 m | 1992–1998 |
| North Cape Tunnel | 1993–1999 |
| Bømlafjord Tunnel | The deepest point of the International E-road network. Connects Stord municipality to the Norwegian mainland | 1997–2000 |
| Eiksund Tunnel | 2003–2008 |
| Xiang'an Tunnel | 2005–2010 |
| Busan–Geoje Fixed Link | 2008–2010 |
| Qingdao Jiaozhou Bay Tunnel | 2006–2011 |
| Marmaray | 2004–2013 |
| Marina Coastal Expressway | 2008–2013 |
| Port of Miami Tunnel | 2010–2014 |
| Eurasia Tunnel | 2011–2016 |
| Hong Kong–Zhuhai–Macau Bridge | 2009–2018 |
| Riachuelo Lot 3 Tunnel | 2017–2019 |
| Ryfast | 2013–2020 |
| Eysturoyartunnilin | 2017–2020 |
| Tuen Mun–Chek Lap Kok Link | 2011–2020 |
| Boryeong Undersea Tunnel | 2012-2021 |
| Musaimeer Outfall Tunnel | Diameter 3.7 m | 2017-2021 |
| Haicang Tunnel | 2016–2021 |
| East West Metro Tunnel | 2021 |
| Bangabandhu Sheikh Mujibur Rahman Tunnel | 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 |
Proposed
Road
-
Rogfast tunnel in Norway – construction having started in 2018, at 27 km length, 392 m depth, it will be the longest road tunnel and deepest undersea tunnel in the world.
-
Karnaphuli Tunnel or Bangabandhu Sheikh Mujibur Rahman Tunnel in Bangladesh Tunnel is an underwater expressway tunnel in the port city of Chittagong, Bangladesh under the Karnaphuli river.
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Underwater Road Tunnel Salamina island-Perama - planned road tunnel in Attica, Greece. Currently at the second stage of the tender from which the concessionaire will be selected.
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India-Sri Lanka Sea Tunnel (proposed)
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Penang Undersea Tunnel in Malaysia – to open in 2025
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Western Harbour Tunnel in Sydney, New South Wales, Australia – to open in 2028
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Suðuroyartunnilin in the Faroe Islands – at least 25 km in length, it would connect the islands of Suðuroy and Skúgvoy to Sandoy, which is part of the fixed-link interconnected Faroese "mainland".
Rail
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Bohai Strait tunnel in China between Dalian and Yantai (decided, construction to start 'as soon as possible'.
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Helsinki to Tallinn Tunnel under the Gulf of Finland (proposed)
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Irish Sea Tunnel (suggested)
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Rio de Janeiro Metro Bay Tunnel (Line 3 – Rio de Janeiro-Niterói) (proposed)
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Fehmarn Belt Fixed Link between Denmark and Germany (decided, construction started in January 2021)
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Mumbai–Ahmedabad high-speed rail corridor of India (decided, construction start November 2018)
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Taiwan Strait Tunnel - if built would become the longest rail tunnel in the world. Engineering challenges and the unsolved political status of Taiwan make construction unlikely
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Strait of Gibraltar Tunnel - linking Gibraltar or the Spanish mainland to the African mainland. If built it would most likely become the deepest tunnel ever built
See also
