The submerged floating tunnel will therefore have to compete with well known structures and therefore have a disadvantage since no submerged floating tunnel has yet to be built. A future owner is then faced with a risk not easily estimated on one hand, on the other hand this new alternative may have certain attractive features especially when environmental considerations become important. This paper presents these various advantages and also points out some obvious disadvantages with this new and challenging structure.
A great step forward would be if a submerged floating tunnel were built somewhere. The proposed structure here in China would certainly generate a lot of interest and suggest the involved parties should prepare for a large number of visitors. 0 201 0 published by Elsevier Ltd. open access under CC BY-NC-ND license. Keyw. rords: Submerged Floating Tunnel; Archimedes Bridge 1. Introduction The submerged floating tunnel, SET, also named as Archimedes Bridge, is a concept going back at least 1 50 years and probably even further back.
Historic records show that a rather complete understanding of this idea was brought forward by Sir James Reed, LIK in 1886 and later in 1924 by Trygve Olsen Dale, Norway. During the last part of 1960 a renewed interest in SET was followed up by the start of some minor research projects and during the following years these efforts increased considerably in Italy, Japan and Norway. Several sites were examined both in Japan and Europe, seminars and meetings were held and SFT as a new structure received increasing interest Several research projects were started and several papers especially from these three countries were published.
The H?gs00rd Project in Norway was probably the most extensive of these projects as this project was taken through fundamental research to evelopment of four alternatives using prequalified contractors to assist in producing detailed design and also complete tender documents. The resulting four alternatives were approved by the * corresponding author. Tel. : +47-91375945. E-mail address: havard. [email protected] no 1877-7058 c 2010 Elsevier Ltd. open access under CC BY-NC-ND license. doi:1 0. 1016/j. proeng. 2010. 08. 003 4 H. ?stlid / Procedia Engineering 4 (2010) 3-11 H. ?stlid / Procedia Engineering 2 (2010) 000”000 2 Norwegian Public Roads Administration and were ready for establishing contracts for the construction of the SFT crossing at H?gsfjord in Rogaland County on the west coast of Norway in 1999. The project was stopped due to political decisions. SET was not so much in focus the following few years but in 2004 a Protocol of Scientific and Technological Cooperation between the Peoples Republic of China and the Italian Republic was signed for the Sino-Italian Joint Laboratory of Archimedes Bridge.
The partners for this were the Chinese Academy of Sciences-Institute of Mechanics and the aim of SIJLA8 was to construct the first Archimedes Bridge (SFT) in the world. This was a very encouraging step in further development and resulted in renewed global interest for this new Structure and several new papers were published especially from Chinese authors and also from Italy and Norway. This paper attempts to look at the competitive characteristics of Archimedes Bridge, SFT, and also discuss some areas of further research and development to increase the competitiveness of a very exciting and promising new structure. . Four principle types of SFT The type of SET in Fig. 1 is independent of water depth, the system is sensitive to wind, waves, currents and possible ships collision. Design should allow for one pontoon to be lost and the structure should still survive. The SET alternative Fig. 2 is an “underwater bridge” with foundations on the bottom , in principle the columns are in compression but they may also be a tension type alternative. Water depth will play an important role in this case and a few hundred meters depth is considered a limit at the present time.
However, much deeper foundations are at present under investigation. Fig. 1. SET with pontoons Fig. 2. SFT supported on columns The SET alternative in Fig. 3 is based on tethers being in tension in all future situations, no slack in these tethers may be accepted in any future load cases. The present practical depths for this type of crossing may be several hundred meters, whether the tethers are vertical or a combination of vertical and inclined. The SET alternative in Fig. 4 is interesting as it has no anchoring at all except at landfalls and is then independent of depth.
There is obviously a limit to the length but only further development will answer this. Perhaps an alternative for light traffic should be designed, possibly a 1 00 or 200 meter long and then by R & D find out where the main problems were. Fig. 3. SFT with tethers to the bottom Fig. 4. SFT unanchored except at landfalls The cross section of SET has a marked effect on hydrodynamic behaviour and response to various load cases. However, the cross section will be decided on the basis of future use, number of lanes for cars, room for pedestrians 5 H. ?stlid / Procedia Engineering 2 (2010) 000-000 3 and various types of services and so on. The cross section may be circular or rectangular or any other geometrical shape as the case may be. A very simple cross section is shown in Fig. 5. Fig. 5. A simple cross section The four alternatives in Fig. 6 were approved by the Norwegian Public Roads Administration for the H?gsfjord Project. These alternatives were designed in considerable detail, also including the construction process and installation.
Future maintenance was also considered together with an extensive instrumentation system. Fig. 6. These four alternatives were approved by the Norwegian Public Roads Administration for the H?gsfjord Project. Both concrete and steel may be used as main construction material, most often in combination in some form 3. What may be possible to build to day? The following statements may be considered to be a little guesswork, but are based on at least some insight and belief in what may be possible today. nanchored : no tethers, no pontoons, just land connections For pedestrians: 300 meters For normal traffic: 1 50 meters x unanchored with pontoons: 1500-2000 meters x With pontoons, two tubes: 3000 meters x With pontoons, two tubes and anchor systems: 4000 meters or more x Tethers, shallow waters, < 200 meters : Any length x Tethers, deep waters > 200 meters : > 4000 meters or more x Tethers, very deep waters, > 600 meters , two tubes: 4000 meters and more x For trains, tethers and pontoons in combinations to produce sufficient vertical and horizontal stiffness 4.
The competitive features of SET A discussion follows of some competitive features of SFT. 6 H. ?stlid / Procedia Engineering 4 (2010) 3-11 H. ?stlid / Procedia Engineering 2 (2010) 000-000 4. 1. Invisible Crossing waterways, whether being from main land to islands in the sea or maybe more important crossing an inland lake, perhaps the one we are at now will in many cases meet protests both from tourist interests and also from the public in general.
Lakes of special beauty or perhaps historical value should be preserved for the future, the crossing of such areas and lakes with SFT may make this possible. An illustration of this may be seen in Fig. 7. 4. 2. ength only from shore to shore Fig. 7 also illustrates that the actual SFT structure is only as long as the distance between the shores. If desired the SET may be connected directly to tunnels and then be completely out of sight for any desired distance. Fig. 7. SET crossing of lakes maybe invisible and preserve the lake and the area as it was before 4. 3.
Sometimes only alternative to ferry If a crossing is very deep and wide, many of the traditional types of bridges, immersed or undersea tunnels may be both technically and economically rohibitive and if a fixed link is wanted an SFT may be the only alternative. Another feature with the SET is the lower energy use for crossing, driving cars on a fixed link will normally use considerably less energy than ferry operations. 4. 4. Very low gradient Crossings with undersea tunnels or bridges will frequently mean longer structures with consequently higher costs and this may offset the higher cost per meter for an alternative SFT.
An SFT crossing may have a very gentle gradient or being nearly horizontal giving considerable savings in energy use by traffic. 4. 5. Access to underground service-parking space at ends As the SFT may continue in tunnels having crossed the waterway, it is possible to arrange parking places or service areas under ground and provide access to the surface by lifts directly into cities or recreational areas as the case may be. See Fig. 8. These possibilities may be one of big advantages in future, in fact for all types of tunnels. H. ?stlid / Procedia Engineering 4 (2010) 3”1 1 7 Fig. . Parking and service areas 4. 6. May surface just above shoreline As an SET may be positioned at any depth below the surface arrangements ay be made that the SET surfaces at or very near the shoreline. This may be an advantage for connections to new or existing road systems and gives the planners freedom to locate connections in a very flexible way. 4. 7. Constructed away from densely populated areas Construction of infrastructure is a major everyday problem in many cities, traffic is piling up, new one way streets daily and generally great frustrations by millions of people.
One very interesting feature with SPT is that the actual construction may be done away from the densely or highly populated areas, a eature also for immersed tunnel construction. After the sections of the tunnel are finished they may be towed to the actual site and there joined together and installed at the desired depth. In some instances the whole length of the SFT may be assembled at the construction site and the complete structure towed to the actual site and installed. This would ensure minimum disturbances to the local area and perhaps the whole operation may only take months instead of years. . 8. Easy removal at end of life All structures will have to be removed or replaced sooner or later and as the mount of structures increase it is important to prepare for these operations already at the planning and design stage. Removal, recycling or reuse of materials or parts of the structures will become increasingly necessary in the future, for both economic and environmental reasons. SFT is in most cases a floating structure as a whole and may therefore be towed away to some place where parts of the SFT may be reused.
One may imagine such an operation by for instance placing bulkheads in the original elements and then separating the SFT in suitable lengths to be perhaps towed to different locations for reuse or destruction. . 9. Some possibilities of reuse or recycling SET Sections of a tunnel may be used for many purposes, depending on its size and condition. One obvious possibility is for various types of storage facilities, whether in the sea or on dry land, a section of tunnel ,say 12 meters in diameter cut to a length of 10 to 15 meters would not present any difficulty to get up on dry land if that was desired.
To cut a concrete tunnel into sections would not present big difficulties either, its more a question of overall economy than technology. 8 As SFT is a floating structure parts it may be towed to any place for use, erhaps as artificial reefs for increased fish production or stimulating growth of marine organisms. Bearing in mind this end of life situation at the design and planning stage may also contribute to increased interest in a steadily growing problem of waste handling and sustainability in our use and reuse of materials. 4. 10. Why has no SET yet been built?
With all the advantages listed above a reasonable question would be: Why has no SFT been built and some answers to this may be the following thoughts. x This Structure is unusual and very little experience if any exists. Both rofessionals, politicians and the public are aware of this and even if spectacular accidents are rather scarce in engineering, these do happen. x Also the fact that the SFT has water all around will also appear alarming to many people, even if most people on boats and ferries frequently travel well below the waterline. Another feature with SFT is that buoyancy provides the necessary bearing capacity for traffic and that the structure has to be anchored down to be kept in position, this may be sometimes difficult to both understand and accept. x New types of structures will often receive very clear reactions, either for or gainst and this seems to be the case for both professionals and the general public. x It is my belief that roads administrations world wide will not approve structures they have any doubts about and it is important that the first SFT proves to be a success.
Seminars and discussions like the one we have here in China now will greatly contribute to an interesting future for SFT, especially the building and research of the model of Archimedes Bridge in Qiandao Lake. 5. Areas for improving SET competitiveness In an effort to establish the present status of SET and suggest areas for trengthening the competitiveness ashort discussion of some possibilities is presented. The opinions and statements are that of the author and should be taken as perhaps a basis for further discussions and not much more than that. The basic SFT design should be presented in a simple and understandable way to everybody, the importance Of clear and good drawings cannot be overemphasized, clear 3-D presentations may be more important than pages of text. x There is quite a number of structures similar to SFT around the world, especially immersed tunnels have many similarities with SET. A large part of mmersed tunnel technology is used for SFT construction and one of the important centers for immersed and floating tunnels may be found in the International Tunnelling and Underground Space Association, ITA.
Working Group 1 1 is dealing with Immersed and Floating tunnels and this is a forum for people interested in SFT and new members are very welcome at the yearly meetings. The structures similar to SFT should be published in SFT literature and reports. This would inform the engineering community about the present experience with these structures and also be a valuable reference of the behaviour of these structures in practice. Some of the more complex technical elements and procedures should be explained, for instance the construction methods of the tunnel, towing procedures, installation, anchoring methods and so on.
This would familiarize the public with this structure and make it more acceptable to be used for great benefit to both local and regional areas. x The structure itself should be studied for technical simplification in all areas. The simpler and clearer the methods and procedures the greater the probability for a good end result. x The structure should be robust and have some reserve capacity in all mportant areas; refinery should come at a later stage when experience is gathered. x In Fig. 9, some concrete areas are proposed for further study H. ?stlid / Procedia Engineering 4 (2010) 3-1 1 9 -Weak link between pontoon and ‘or connections to SET -Distance between size and shape of pontoons -For very deep waters, additional anchoring methods may be necessary -Design of columns, connections to SET and foundations -Study of limiting depths -Installation procedures -Foundation methods on sea bottom -Spacing and arrangement of tethers -Possible tether adjustments through service life For very deep waters, horizontal anchoring systems -Interesting alternative, determine possible lengths for: -Pedestrian use only -Normal traffic -Other uses, pipes, cables etc.
Fig. 9. Areas for further studies Perhaps the greatest improvements of competitiveness is producing a big model then perform some tests and measurements of response to various types of loadings and after that building a full scale structure as in fact is the plan here in China. 6. A possible future for SET Looking at a world with increasing demand for transport, new technology will produce new methods and the demand for transporting large number of eople over long distances will also increase. One such method could be very long SET s.
A vision could be to connect continents in the distant future or maybe not so distant future after all. At present trains are already approaching a speed of at least 6-700 km/h, with further development of MAGLEV systems, speeds getting close to the speed of sound may not be far away. Some of the many problems with such a system have been discussed for a number of years, suffice to mention a few in this presentation. In any case a, possible place to study such a crossing should be selected carefully nd preferably be made a global effort where scientists and professionals from many parts of the world could participate.