underwater 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.{{Citation|last=Gursoy|first=Ahmet|title=Immersed Tube Tunnels|date=1996|url=https://doi.org/10.1007/978-1-4613-0449-4_14|work=Tunnel Engineering Handbook|pages=268–297|editor-last=Bickel|editor-first=John O.|place=Boston, MA|publisher=Springer US|language=en|doi=10.1007/978-1-4613-0449-4_14|isbn=978-1-4613-0449-4|access-date=2022-02-17|editor2-last=Kuesel|editor2-first=Thomas R.|editor3-last=King|editor3-first=Elwyn H.|url-access=subscription}} 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.{{Cite journal|last=Ingerslev|first=Christian|date=2010-01-01|title=Immersed and floating tunnels|journal=Procedia Engineering|series=ISAB-2010|language=en|volume=4|pages=51–59|doi=10.1016/j.proeng.2010.08.007|issn=1877-7058|doi-access=free}}

{{Further|Tunnel#Choice of tunnels versus 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.

File:Helsinki-tallinna.JPG 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[http://www.poferries.com/tourist/content/pages/template/routes_dover_-_calais_timetable_timetable_DOCA.htm Dover–Calais Ferry Times], poferries.com website. and 21 minutes on the Eurostar). Ferries offer much lower frequency and capacity{{citation needed|date=August 2019}} 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.

{{Unsourced section|date=November 2023}}

Tunnels require far higher costs of security and construction than bridges.{{citation needed|date=October 2020}} 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.

• 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.
• 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.{{Cite web|title=Undersea Road Tunnel Salamina island - Perama|url=https://ec.europa.eu/eipp/desktop/el/projects/project-72.html|website=ec.europa.eu|access-date=2020-05-13}}{{Cite web|title=Design for Salamina island undersea road tunnel, finalized|url=https://ypodomes.com/design-for-salamina-island-undersea-road-tunnel-finalized/|last=Καραγιάννης|first=Νίκος|date=2020-05-12|website=Ypodomes.com|language=el|access-date=2020-05-13}}
• India-Sri Lanka Sea Tunnel (proposed) {{Cite news|title=India to build sea bridge, tunnel to connect Sri Lanka at a cost of Rs 24,000 crore|url=https://economictimes.indiatimes.com/news/economy/infrastructure/india-to-build-sea-bridge-tunnel-to-connect-sri-lanka-at-a-cost-of-rs-24000-crore-nitin-gadkari/articleshow/50205132.cms?from=mdr|newspaper=The Economic Times| date=16 December 2015 }}
• Penang Undersea Tunnel in Malaysia – to open in 2025
• Western Harbour Tunnel in Sydney, New South Wales, Australia – to open in 2028
• 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".

• Bohai Strait tunnel in China between Dalian and Yantai (decided, construction to start 'as soon as possible'.{{Cite web|url=http://dalian.runsky.com/2018-03/21/content_5816155.html|archiveurl=https://web.archive.org/web/20180728131522/http://dalian.runsky.com/2018-03/21/content_5816155.html|title=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|archivedate=July 28, 2018|website=dalian.runsky.com}})
• Helsinki to Tallinn Tunnel under the Gulf of Finland (proposed)
• Irish Sea Tunnel (suggested)
• Rio de Janeiro Metro Bay Tunnel (Line 3 – Rio de Janeiro-Niterói) (proposed)
• Fehmarn Belt Fixed Link between Denmark and Germany (decided, construction started in January 2021)
• Mumbai–Ahmedabad high-speed rail corridor of India (decided, construction start November 2018)
• 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
• 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

• Immersed tube tunnel
• Intercontinental and transoceanic fixed links
• Shark tunnel

{{Reflist}}

{{more citations needed|date=August 2010}}

{{Commons category|Undersea tunnels}}

{{Authority control}}

*

Category:Coastal construction