# Submerged floating tunnel

Diagram of the buoyancy effect

A submerged floating tunnel (SFT), also called a suspended tunnel or Archimedes bridge, is a tunnel that floats in water, supported by its buoyancy (specifically, by employing the hydrostatic thrust, or Archimedes' principle).[1]

The tube is placed underwater, deep enough to avoid water traffic and weather, but not so deep that high water pressure needs to be dealt with—usually 20–50 m (60–150 ft) is sufficient. Cables either anchored to the Earth[1] or to pontoons at the surface[2] prevent it from floating to the surface or submerging, respectively.

## Construction

Two types of submerged floating tunnels

The concept of submerged floating tunnels is based on well-known technology applied to floating bridges and offshore structures, but the construction is mostly similar to that of immersed tunnels: One way is to build the tube in sections in a dry dock; then float these to the construction site and sink them into place, while sealed; and, when the sections are fixed to each other, the seals are broken. Another possibility is to build the sections unsealed, and after welding them together, pump the water out.

The ballast used is calculated so that the structure has approximate hydrostatic equilibrium (that is, the tunnel is roughly the same overall density as water), whereas immersed tube tunnels are ballasted more to weight them down to the sea bed. This, of course, means that a submerged floating tunnel must be anchored to the ground or to the water surface to keep it in place (which of these depends on which side of the equilibrium point the tunnel is).

## Applications

Water-spanning structures: 1: Suspension bridge 2: Submerged floating tunnel 3: Immersed tube 4: Undersea tunnel

Submerged floating tubes allow construction of a tunnel in extremely deep water, where conventional bridges or tunnels are technically difficult or prohibitively expensive. They would be able to deal with seismic disturbances and weather events easily (as they have some degree of freedom in regards to movement), and their structural performance is independent of length (that is, it can be very long without compromising its stability and resistance).

On the other hand, they may be vulnerable in regards to anchors or submarine traffic, which therefore has to be taken in consideration when building one.

Likely applications include fjords, deep, narrow sea channels, and deep lakes.[3]

## Proposals

A submerged floating tunnel has never been built, but several proposals have been presented by different entities.

late 1800s English Channel United Kingdom Sir Edward James Reed [4]
1969 Strait of Messina Italy Alan Grant[disambiguation needed] [5]
April 16, 2003 Transatlantic tunnel N/A Discovery Channel's Extreme Engineering (Season 1, episode 3) [10]
? Funka Bay, Hokkaido Japan Society of Submerged Floating Tunnel Technology [11][12]
? Lake Washington, Seattle United States James Felch / Subterra, Inc. [13][5][12]
? Vancouver Island Canada Ministry of Transportation of British Columbia, Canada [14]
? Lugano Lake Switzerland [5]

### Europe

Ponte di Archimede International, an Italian company, investigated the SFT in collaboration with the Norwegian Roads Research Laboratory,[15] the Danish Road Institute and the Italian Shipping Register, with a financial grant from the European Union and the coordination of FEHRL (Forum European National Highway Research Laboratories) an International Association of over 30 National Road Centres.[16] Furthermore the Provincial Administrations of Como (Como Lake) and Lecco, in Italy, have officially shown great interest in the Archimede's Bridge for crossing the Lario and the study of the submerged floating tunnel in the Strait of Messina has been promoted by Ponte di Archimede S.p.A. and verified with a feasibility analysis by the Italian Naval Register (RINA).[17] In Norway, interest has been revived with Norwegian Public Roads Administration (NPRA) investigating the technical and economic potential for eliminating all ferries on fjord crossings along the western corridor (E39) between Kristiansand and Trondheim.[18] This project also linked with FEHRL through the Forever Open Road programme.[19]

According to Elio Matacena, the President of Ponte Archimede di International, the only constraint to build such tunnels in deeper waters is the price of the structure. Namely, the cables, which are very expensive, would be very long. He also refers that the bridge is capable of supporting more weight than a traditional bridge, which has very strict weight limits, while being up to two times cheaper. Matacena points out that the environmental studies carried on show that the bridge would have a very low impact on the aquatic life.[20]

### China

The SIJLAB (Sino-Italian Joint Laboratory of Archimedes' Bridge), created in 1998, between Institute of Mechanics, Chinese Academy of Sciences, China and Ponte di Archimede S.p.A., is financed by the Italian Ministry of Foreign Affairs, the Chinese Ministry of Science and Technology and the Institute of Mechanics of the Chinese Academy of Sciences.

The consortium has started to build a 100m demonstration tunnel in Qiandao Lake in China eastern province of Zhejiang. Inside it, two layers of one-way motorways will run though in the middle, with two railway tracks flanking them.[21] The Qiandao Lake prototype will serve to help plan for the project of a 3,300-meter submerged floating tunnel in the Jintang Strait, in the Zhoushan archipelago, also situated in Zhejiang.[22][23][24]

### Indonesia

Indonesia has also expressed interest in this technology. For the infrastructure, that would connect Bali to Java Island, there were two options, a conventional bridge or the undersea tunnel.

On 2004 the tunnel option was more widely discussed, specially when Kwik Kian Gie, then the Minister of National Development announced that a European consortium was interested in investing in the undersea tunnel between Java and Sumatra. The budget was told to be around 15 billion US dollars for the undersea tunnel in the Sunda Strait; in long term it would link up Bali, Java, Sumatra, Malaysia and Thailand in an uninterrupted chain. The project was planned to start construction in 2005 and be ready to use by 2018, and was a part of the Asian Highway.[25]

However, the bridge option was later favored.[26]

In 2007, Indonesian experts, led by Ir. Iskendar, Director for the Center of Assessment and Application of Technology for Transportation System and Industries, participated in a meeting with SIJLAB engineers, from the sino-Italian Archimedes Bridge project.[23][27] As an archipelagic country, consisting of more than 13 thousand islands, Indonesia could benefit of such tunnels. The conventional transportation service between islands is made mainly by ferries. Archimedes bridges (Terowongan Dasar Laut, in Indonesian) could thus be an alternative to connect adjacent islands, in addition to bridges.

## References

1. ^ a b Zanchi, Flores (July 2002). "Archimedes Bridge". Floornature. Archived from the original on 2008-01-11. Retrieved 2007-02-11.
2. ^ "Italian bridges cultures". Beijing Official Web Portal. Archived from the original on 2008-01-11. Retrieved 2007-09-13.
3. ^
4. ^ Tunnel Visions; July 1997; Scientific American Magazine; by Gary Stix
5. ^ a b c http://www.daps.unina.it/doc/doc_new/Brochure_Sijlab.pdf
6. ^ "Konkurranse om fjordkryssing" Norwegian Public Roads Administration, 7 May 2012. Accessed: 13 October 2013.
7. ^ "Ferry-free E39: Rørbruer (Tube bridges)" page 60 Norwegian Public Roads Administration, December 2012. Accessed: 13 October 2013.
8. ^ Rørbru
9. ^
10. ^ Discovery Channel:: Extreme Engineering: Transatlantic Tunnel – Interactive presentation of the theoretical structure of the transatlantic tunnel
11. ^ Sato Motohiro, Kanie Shunji and Mikami Takashi (Graduate School of Engineering, Hokkaido University): Wave response characteristics of Submerged Floating Tunnel modeled as a beam on elastic foundation. Journal of Structural Engineering, vol. 48A; No.1; pp 27–34 (2002)
12. ^ a b "Groups promoting the SFT concept". Norwegian Submerged Floating Tunnel Company AS. Retrieved 2008-08-22.
13. ^ "Submerged Floating Tunnel across Lake Washington". SubTerra, Inc. 2001.
14. ^ "A Potential Fixed Link to Vancouver Island". Ministry of Transportation, British Columbia. 2001.
15. ^ http://www.fehrl.org/index.php?m=203
16. ^ http://www.fehrl.org
17. ^ "Ponte di Archimede S.p.A. — Research and Development" (PDF). pp. 6–7. Retrieved 2008-08-22.
18. ^ Olav Ellevset. "Coastal Highway Route E39" Norwegian Public Roads Administration Accessed: 13 October 2013.
20. ^ Maria Pia Medina Luna (2006-10-21). "Le premier pont-tunnel submergé reliera en Chine le continent à une île sur 3 200 m" (in French). L'Internaute — Magazine Savoir. (French)
21. ^ China to build world's 1st 'Archimedes bridge'
22. ^ "Archimedes Bridge". Ponte di Archimede International S.p.A.
23. ^ a b "First Archimedes bridge prototype to be realized in southern China". People's Daily Online. April 18, 2007.
24. ^ Zhejiang University Health Monitoring & Controlling Studying of Large-scale Bridge & Tunnel Structure (2006). "Research about suspending tunnel".
25. ^
26. ^
27. ^ Institute of Mechanics, Chinese Academy of Sciences: Indonesian Experts visited IMECH