Many places around the world are planning to build floating tunnels. These are tunnels placed in water at a certain depth below the surface, or at the bottom of the sea. Typically, such tunnels are intended to connect the shores of the island to the mainland, or to connect the shores of large bays.
The farthest in the design of such tunnels went Norwegians who are planning the project "E39 without ferry" which would halve the driving time thanks to new bridges and tunnels. One of the tunnels will set a world record, located below the 400-meter-deep fjord, and will be about 28 kilometers long. Located between the two sides of the fjord at a depth of about 30 meters below the surface, it will allow the largest ships to sail freely. It will have two concrete tunnel pipes, one for traffic in each direction, and will be erected and attached to floating pontoons, 250 meters apart, to allow passage of large ships.
In order for such large pipes to stand in one place in the water, they must be anchored to the bottom.
If the bottom is too deep, it is easier to hold them at a certain height so that they are heavier than water and are held at a certain depth by large floating pontoons every few hundred meters.
The disadvantage of this solution is that pontoons rise at high tide or high waves, and with them tunnel pipes rise. In this way, these pipes go up and down several times each day, changing the length of their junction with the terrestrial part of the tunnel. Large oscillations occur at the junction and very permanent sliding surfaces need to be made.
If the sea is a shallow, tunnel tube is better to make it lighter than water to keep the buoyancy at a certain depth determined by anchoring for the bottom. In this way, the connection with the terrestrial part of the tunnel is much more stable, since the change in the length of the tunnel can only occur in the event of a major change in sea temperature, while the tide does not affect the length of the tunnel. In the shallower sea, the tunnel would only partially float at a certain depth, while it would mostly lie at the bottom of the sea, at locations where the sea is shallow 30 to 40 meters.
The problem with floating tunnels is the potential explosions in the tunnel and the possible impact of the submarines into the tunnel.
In the tunnel there is a great pressure of water from the outside inwards, while a potential explosion has the opposite pressure.
The submarine's potential impact on the floating tunnel is also a great danger.
To reduce the risk of impact, it is necessary to illuminate the tunnel from the outside in order to be visible. On the parts of the tunnel lying at the bottom, impact protection is easier since it is sufficient to make stone embankments on both sides to protect the tunnel from impact.
On the floating part of the tunnel route, protection is more difficult.
The first and most important protection is the solid concrete formwork of the reinforced concrete tunnel, which also contains additional glass threads that reinforce the concrete.
The second level of protection is the lining of pipes with a thick elastic material such as foam rubber, or plastic pipes wrapped around concrete pipes.
The third level of protection could be a large net set up around the tunnel at a distance of 20 to 30 meters on each side of the tunnel.
This kind of safety net is shown in the picture above.
The net (5) is mounted on plastic floating tubes (4) that extend parallel to the tunnel tubes (1). These plastic float tubes (4) are connected to the tunnel tubes (1) by solid steel spiral buffers (3).
In the event of a submarine impact, it would first strike the safety net (5), losing some of the impact energy, and the tunnel tubes (1) moving slightly in the opposite direction. If this did not stop the submarine, it would strike at a reduced speed in the elastic liner located on the tunnel tubes themselves, and the tunnel tubes (1) would move slightly in the opposite direction. Only with the rest of the force would the submarines act on the reinforced concrete tunnel tubes (1) themselves, which could move further in the opposite direction from the impact force. Due to the fact that the tunnel pipes have the ability to move horizontally, the danger of pipe bursting is much smaller and the safety of the passengers through the tunnel would be greater.
In order for such tunnels to be built quickly, it is possible to apply the construction technique by joining prefabricated elements previously built in dry dock yards.
In dry docks, round reinforced concrete pipes of ten meters wide and 200 - 300 meters long would be able to produce constructed. These pipes would be fitted with steel multi-door doors that would prevent water from entering the pipes. In this way, the tunnel pipes (1) would float on the water like ships and could be towed by the surface of the water to the place of installation.
Together with the tunnel pipes (1), connection pipes (2) could be constructed in the shipyards, which would serve as joints between tunnel pipes (1). These connecting pipes (2) should also have multiple mounting doors at their openings that prevent water from entering during surface water transport.
Two tunnel pipes (1) on one side and two on the other would be connected to the connecting pipes (2). These connecting pipes (2) also have one smaller pipe that cross-links the left and right tunnel pipes (1).
In this way, after floating tunnels are installed through these connecting pipes (2), people on one side of the tunnel could, in case of need, or risk crossing the other side of the tunnel where traffic is going in the other direction.
After mounting the tunnel tubes (1) with connecting tubes (2) at the installation location, and after anchoring the floating tunnel to the bottom, the tunnel tubes (1) would drop to the required depth by the weight of the anchors. After that, multiple doors would be pulled from the inside, one after the other. In this way, the passage through the floating tunnel would become open and the sewerage, asphalt paving, air conditioning and other installations could be switched. The weight of all installed components (together with later vehicles) should be less than the buoyancy of the tunnel tube (1) by its volume.
Thanks to this technology of assembling a floating tunnel of pre-built elements, construction could be completed in a few months and the cost of construction could be many times lower than if the pipes were made by concreting on the shore and pushed into the sea.
This would allow cheap and fast connection of numerous islands without compromising the normal navigation between the islands.