Submerged Floating Tunnel (SFT), also called Archimedes Bridge or Suspension Tunnel,
It is a tunnel that floats in water, supported by its buoyancy through the use of hydrostatic propulsion.
Tunnels in water are not new in civil engineering. Since approximately the twentieth century,
many submerged tunnels have been constructed around the world.
Bridges and tunnels are the most common structures used to cross bodies of water.
In some cases, submerged tunnels extend under the sea or river bed.
But submerged floating tunnels are used when the bed is very rocky, deep or undulating.
Features of floating tunnel
The floating tunnel is a new concept that has never been built before, but several proposals have been put forward by different entities.
It is noted that the depth of the tunnel varies from one place to another to a greater extent,
and the maximum depth can reach 8 km and the average depth is 3.3 km.
The two alternatives available for construction are a bridge above water level or a tunnel below ground level.
However, since the depth is 8 km, it is impossible to construct concrete columns of this height for the bridge.
Also, the pressure below 8 kilometers above sea level is about 500 times the atmospheric pressure,
So one cannot survive in this high pressure area.
Therefore, the optimal depth for the floating tunnel is 30 meters from sea level,
where there is no problem due to high pressure.
This would be enough for any large ship to pass through the SFT unhindered.
Basic principles of submerged floating tunnel
A submerged floating tunnel is a floating structure that moves in the water.
The relationship between buoyancy and self-weight is very important because it controls the static behavior of the tunnel, in response to dynamic forces.
The submerged floating tunnel can be floated in two ways:
In this type, the submerged floating tunnel is installed by installing tension legs at the bottom or pontoons at the surface.
Here, the submerged floating tunnel is essentially located 30 meters below the surface of the water.
- Negative buoyancy
The foundations are piers or columns for the sea floor or lake bottom in this type.
This method is limited to a depth of 100 meters of water,
where the submerged floating tunnel is exposed to all the typical environmental procedures in the aquatic environment:
Such as current, waves, water level vibration, erosion, earthquakes, ice, and marine growth.
Therefore, it should be designed to withstand all actions,
operational and incidental loads, with sufficient strength and rigidity.
Transverse rigidity is provided by bottom fastening.
Features of submerged floating tunnel
Crossing waterways, whether from the mainland to islands in the sea or crossing an inland lake, may in many cases raise objections from environmentalists and the public at large.
But, on the other hand, lakes of special beauty or historical value should be preserved for the future;
Crossing these areas and lakes by SFT may make this possible without affecting the surrounding natural environment.
The submerged floating tunnel structure reaches the same length as the distance between the two shores.
The submerged floating tunnel may be connected directly to the tunnels and thus completely out of sight for any desired length.
Very low gradient
Bridge crossings or subsea tunnels often mean longer construction and therefore higher costs, resulting in a higher price per meter for an alternative submerged floating tunnel.
In addition, a submerged floating tunnel crossing may have a very gentle gradient or be nearly horizontal, providing significant energy savings for traffic.
Access to underground parking
It is possible to arrange service areas or underground parking spaces and access to the surface by lifts directly to the town or city.
These possibilities may be one of the biggest advantages in the future for all types of tunnels.
The surface is just above the shoreline
The submerged floating tunnel can be placed at any depth below the surface, and arrangements can be made so that its surface is very close to shore.
This arrangement should be useful for connections to new or existing road systems and allow planners to create links flexibly.
Building away from densely populated areas
The main problem that many cities face these days is traffic congestion.
Converting two-way streets into one-way streets.
Therefore, constructing a submerged floating tunnel is a viable option that can be implemented in densely populated cities to relieve traffic congestion.
After the tunnel sections are completed, they are pulled to the actual location and installed to the required depth.
This would complete the entire process in months rather than years and ensure minimal disruption to the local area.
Easy removal at end of life
All structures must be replaced or removed sooner or later once the life of the structure is complete.
It becomes important to consider removal/dismantling operations at the planning and design stage.
In addition, the removal, recycling or reuse of materials or parts of structures will become increasingly necessary for environmental and economic reasons.
In most cases, the SFT is a floating structure as a whole,
and can therefore be towed away somewhere where parts of the SFT can be reused.
Possibilities of reuse of submerged floating tunnel
Depending on their size and condition, tunnel sections can be used for many purposes.
One obvious possibility is for different types of storage facilities, whether on dry land or at sea,
A section of the tunnel with a diameter of 10 meters,
cut into a length of 10 to 12 meters, will not pose any difficulty in getting up.
Challenges facing the adoption of submerged floating tunnel
Since a lot of materials and machinery are used in the project, the estimated cost is almost double that of a regular tunnel.
It becomes difficult to rescue people if a fire breaks out in the train while they are in the tunnel.
If two trains or vehicles collide, it is not easy to save the passengers.
Discomfort in training passengers
When a train passes through a tunnel, pressure waves are generated that propagate along the tunnel at nearly the speed of sound.
These pressure differences may be transmitted to the inside of the trains, unless they are pressure sealed,
It may cause discomfort to train passengers.