Undersea_tunnel

Underwater tunnel

Underwater tunnel

Tunnel which passes under sea

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

Further information: 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. 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[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.

Disadvantages

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.

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

More information Name, Place ...

Proposed

Road

Rail

See also

References

  1. [1]
    Sullivan, Walter. Progress In Technology Revives Interest In Great Tunnels, New York Times, June 24, 1986. Retrieved 15 August 2010.
  2. [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. [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. [4]
    Dover–Calais Ferry Times, poferries.com website.
  5. [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. [6]
    "The Massachusetts Bay Outfall". Massachusetts Water Resources Authority. Retrieved 29 March 2021.
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    "Eysturoyartunnilin verður liðugur í 2019". sjovarkommuna.fo. Archived from the original on June 13, 2018.
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    "Faroe Islands: Inside the undersea tunnel network". BBC News. 4 December 2020. Retrieved 4 January 2021.
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    "The Eysturoy tunnel". Eystur- og Sandoyatunlar.
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    "Eysturoy tunnel built by NCC opened in Faroe Islands". NCC. 19 December 2020.
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    "Kolkata Metro's TBM S639 Crosses Halfway Mark Under Hooghly". The Metro Rail Guy. 2017-05-05. Retrieved 2023-02-14.
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    "Watch: PM Modi takes Kolkata Metro ride with students in India's 1st underwater tunnel". Hindustan Times. 2024-03-06. Retrieved 2024-03-06.
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    "Undersea Road Tunnel Salamina island - Perama". ec.europa.eu. Retrieved 2020-05-13.
  14. [14]
    Καραγιάννης, Νίκος (2020-05-12). "Design for Salamina island undersea road tunnel, finalized". Ypodomes.com (in Greek). Retrieved 2020-05-13.
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    "India to build sea bridge, tunnel to connect Sri Lanka at a cost of Rs 24,000 crore". The Economic Times. 16 December 2015.
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    "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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