Underwater cabling. How it's done
In early July, I prepared an interesting for the community publication on deep-sea communication cables , in which the main emphasis was placed on the design features of a deep-water cable compared to our usual optics. Unfortunately, very little attention was paid to the process itself and the methods of laying the cable along the bottom of rivers, seas and oceans. Now I want to correct this situation and acquaint you with brief information about how communication lines are laid, including in such difficult conditions as the aquatic environment.
In the comments to the previous material a reasonable question arose, what kind of black device is schematically depicted on the gif showing the cable laying process?
Surprisingly, this device is called a submarine cable layer . Based on the design, cable layers are divided into several types:
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The knife cable layer is an analogue of the plow and has a very uncomplicated design: a working wedging knife and a front knife, drums, on which the laying cable is wound, cassettes, rollers, reducing friction of the cable inside the cassette. The cable cutter is towed during operation. In the example of the schematic diagram below, a tractor or other traction machines on a wheeled or tracked track can be used.
The principle of operation of the cable cutter is as follows: When moving, the working knife splits the ground, forms a trench between the ground surface and its splitting part, the depth of which reaches 1.5 meters. An empty cassette is attached to the back of the knife on the hinges, through which the cable (or several cables at once) is passed and is placed on its bottom.
There are also self-contained models on their own, not requiring towing.
However, if you think that it is enough to stick a knife and begin to pull, you are deeply mistaken. For different types of soil, there are rules and recommendations for conducting preparatory activities before using the cable layer. In the first place - this is the so-called proportion or otherwise loosening of the soil. The intensity and scale of the preparatory work depends directly on the type of soil. It is clear that digging soft ground is easier than rock, and the chance to run into obstacles in the process is much lower.
A separate subtype is the submarine cable layer . It is necessary to bury the cable in the ground in coastal areas in order to protect it from anchors, trawls and other human and animal activities. This method is used in coastal areas at shallow depths. The device itself moves along the bottom on special runners. A conventional submarine cable layer breaks through a not very wide, 0.1 - 0.2 m, and a shallow, ~ 0.7 m, trench into which the cable is laid. The equipment itself is towed by the vessel at a speed of approximately 3 km / h and connected with it by a separate cable to monitor the state of the device itself and the work it is doing.
The rotor cable layer is a self-propelled rotor excavator with a trailer cart equipped with devices for loading, transporting and laying cable. This cable layer is used for cable laying in both thawed and frozen soils. The main working device of the rotary cable layer is a disk with cutting teeth. The capacity of the rotary cable layer is up to 1 km of trench per day.
The principal difference in construction compared to the knife cable layer is the mechanism for digging a trench:
The well-established name of such a device is KVG - Vibrating Hydraulic Cable Layer, although in reality it is a knife-type device.
PGKU or Underwater Hydraulic Cable Layers are used when laying cables across rivers and other water barriers using ships. To, in fact, hydraulic borax, which is the main working part of the mechanism, is connected to the hose / pipe going to the pump, placed on the vessel. A jet of water is fed to the drill under pressure, which loosens the rock and pierces a trench in the ground for subsequent cable laying.
It is worth remembering that laying the cable in the ground under water is necessary only at shallow depths. When laying cables in the open ocean, it simply fits to the bottom (depth up to 8 km!), Where nothing but sea water and pressure threatens it (except for force majeure in the form of seismic activity).
If everything is clear with instillation into the ground, then how to stretch the cable through the water can cause a number of questions.
By shallow water obstacles are meant streams, small lakes, narrow marshes and rivers, including mountain ones.
With a depth of less than 0.8m to spec. equipment is not used and stacked as well as along the entire length of the route. With a river depth of 0.8 to 6.0m, an underwater cable layer is used.
Before laying the cable produced a huge amount of preparatory work. I will omit the moment about the need to prepare the infrastructure and obtain permits, and proceed directly to the preparation before starting the cable layer. From the events held are the following:
The cable-laying run through narrow (less than 300 m) rivers is carried out with the help of a tractor column thrust.
A significant role in the course of work and the area in which they are held. For example, freezing of the water surface and the formation of a thick layer of ice capable of withstanding people and wheeled-tracked equipment, surprisingly, greatly simplifies the process if cable-laying vessels (distance of 400 meters or more) had to be used at this segment. The workers are lane (cut in the ice), through which it falls on the prepared cable bottom.
If you stretch a cable through narrow rivers, you can use mechanized equipment located on the other side, then you need to use specially equipped barges or ships to carry out cable laying activities on wide rivers, as well as in coastal areas and the open sea.
As mentioned above, hydraulic cable layers are popular for working under water. This is quite reasonable: the river or seabed is more malleable than frozen soil or rock, and the effort of a water jet under pressure will be enough to “cut through” a gap in the ground for further cable laying.
It is worth noting that the cable is laid in trenches at depths of up to 1500-2000 m due to fishing activities and other factors. In such situations, you have to use the stacking principle, or simply put a giant plow on the bottom of a gigantic sea, which plows it and allows you to protect the cable from tackles and other troubles. At great depths, for obvious reasons, powerful, reinforced cables are used that simply fit to the ground.
Photo of the plow, with an estimated working depth of 2000 meters
If in the case of small distances a single piece of cable is used, then when laying into the sea, the distances increase by several times, and the linear length of the cable coil is limited. Plus, when transmitting a signal over long distances, it is distorted and attenuated. To compensate for these losses, taking into account the cable construction described in the previous article, signal amplifiers and repeaters are used at the splicing points or at other necessary sites. There are no power problems, the design of the fiber optic cable implies the ability to transfer current from which the equipment placed at a distance of up to 150 km from each other is powered.
Here is what a signal amplifier looks like before installation, in partial parsing:
And so it looks ready to be laid at the bottom of the ocean:
As mentioned above, repeaters, depending on the properties of the cable and the circumstances of installation, can be mounted with a frequency of up to 150 km. Modern industry allows the manufacture and delivery of cables with an average length of 5 and sometimes 25 km, which is significantly less than the distance of the repeaters. In these cases, the end of one coil is spliced ​​with a new one, and the junction is protected by a so-called docking box (see the example of such a construction below):
Box parsed:
In turn, repairing, for example, a break in an already laid cable is not a simple matter, although the procedure itself is schematically very banal. With the help of the vessel, one ragged end is lifted to the surface and fixed to the buoy, then the second end of the cable is also pulled up and lifted. The part into which water has penetrated under pressure is cut off, and to connect the ends, use repair cable “trimming”, specially reserved for this. In general, everything looks simple and logical: cut, trimmed, twisted, works. But the scale of such a “twist” is amazing, and it has little relation to the installation itself. If you're lucky, I can talk about this procedure separately.
I hope you enjoyed this material.
But first about the main thing. About equipment
In the comments to the previous material a reasonable question arose, what kind of black device is schematically depicted on the gif showing the cable laying process?
Surprisingly, this device is called a submarine cable layer . Based on the design, cable layers are divided into several types:
')
- Knife
- Rotary
- Hydraulic
The knife cable layer is an analogue of the plow and has a very uncomplicated design: a working wedging knife and a front knife, drums, on which the laying cable is wound, cassettes, rollers, reducing friction of the cable inside the cassette. The cable cutter is towed during operation. In the example of the schematic diagram below, a tractor or other traction machines on a wheeled or tracked track can be used.
The principle of operation of the cable cutter is as follows: When moving, the working knife splits the ground, forms a trench between the ground surface and its splitting part, the depth of which reaches 1.5 meters. An empty cassette is attached to the back of the knife on the hinges, through which the cable (or several cables at once) is passed and is placed on its bottom.
There are also self-contained models on their own, not requiring towing.
However, if you think that it is enough to stick a knife and begin to pull, you are deeply mistaken. For different types of soil, there are rules and recommendations for conducting preparatory activities before using the cable layer. In the first place - this is the so-called proportion or otherwise loosening of the soil. The intensity and scale of the preparatory work depends directly on the type of soil. It is clear that digging soft ground is easier than rock, and the chance to run into obstacles in the process is much lower.
A separate subtype is the submarine cable layer . It is necessary to bury the cable in the ground in coastal areas in order to protect it from anchors, trawls and other human and animal activities. This method is used in coastal areas at shallow depths. The device itself moves along the bottom on special runners. A conventional submarine cable layer breaks through a not very wide, 0.1 - 0.2 m, and a shallow, ~ 0.7 m, trench into which the cable is laid. The equipment itself is towed by the vessel at a speed of approximately 3 km / h and connected with it by a separate cable to monitor the state of the device itself and the work it is doing.
The rotor cable layer is a self-propelled rotor excavator with a trailer cart equipped with devices for loading, transporting and laying cable. This cable layer is used for cable laying in both thawed and frozen soils. The main working device of the rotary cable layer is a disk with cutting teeth. The capacity of the rotary cable layer is up to 1 km of trench per day.
The principal difference in construction compared to the knife cable layer is the mechanism for digging a trench:
The well-established name of such a device is KVG - Vibrating Hydraulic Cable Layer, although in reality it is a knife-type device.
PGKU or Underwater Hydraulic Cable Layers are used when laying cables across rivers and other water barriers using ships. To, in fact, hydraulic borax, which is the main working part of the mechanism, is connected to the hose / pipe going to the pump, placed on the vessel. A jet of water is fed to the drill under pressure, which loosens the rock and pierces a trench in the ground for subsequent cable laying.
It is worth remembering that laying the cable in the ground under water is necessary only at shallow depths. When laying cables in the open ocean, it simply fits to the bottom (depth up to 8 km!), Where nothing but sea water and pressure threatens it (except for force majeure in the form of seismic activity).
If everything is clear with instillation into the ground, then how to stretch the cable through the water can cause a number of questions.
Small water barriers
By shallow water obstacles are meant streams, small lakes, narrow marshes and rivers, including mountain ones.
With a depth of less than 0.8m to spec. equipment is not used and stacked as well as along the entire length of the route. With a river depth of 0.8 to 6.0m, an underwater cable layer is used.
Before laying the cable produced a huge amount of preparatory work. I will omit the moment about the need to prepare the infrastructure and obtain permits, and proceed directly to the preparation before starting the cable layer. From the events held are the following:
- Cutting of coastal slopes with a bulldozer or an excavator to ensure a smooth descent of the cable layer from the shores and its exit from the water;
- Having washed out by hydromonitors the obstacles found during diving inspection and their removal from the road;
- Two or three times the proportion of soil on the planned route;
- Checking the tightness of the cable sheath by excessive air pressure, test with direct current, continuity test;
- Loading the cable on the cable layer and access to the main stage of work.
The cable-laying run through narrow (less than 300 m) rivers is carried out with the help of a tractor column thrust.
A significant role in the course of work and the area in which they are held. For example, freezing of the water surface and the formation of a thick layer of ice capable of withstanding people and wheeled-tracked equipment, surprisingly, greatly simplifies the process if cable-laying vessels (distance of 400 meters or more) had to be used at this segment. The workers are lane (cut in the ice), through which it falls on the prepared cable bottom.
Cable laying on the bottom when using the vessel
If you stretch a cable through narrow rivers, you can use mechanized equipment located on the other side, then you need to use specially equipped barges or ships to carry out cable laying activities on wide rivers, as well as in coastal areas and the open sea.
As mentioned above, hydraulic cable layers are popular for working under water. This is quite reasonable: the river or seabed is more malleable than frozen soil or rock, and the effort of a water jet under pressure will be enough to “cut through” a gap in the ground for further cable laying.
It is worth noting that the cable is laid in trenches at depths of up to 1500-2000 m due to fishing activities and other factors. In such situations, you have to use the stacking principle, or simply put a giant plow on the bottom of a gigantic sea, which plows it and allows you to protect the cable from tackles and other troubles. At great depths, for obvious reasons, powerful, reinforced cables are used that simply fit to the ground.
Photo of the plow, with an estimated working depth of 2000 meters
If in the case of small distances a single piece of cable is used, then when laying into the sea, the distances increase by several times, and the linear length of the cable coil is limited. Plus, when transmitting a signal over long distances, it is distorted and attenuated. To compensate for these losses, taking into account the cable construction described in the previous article, signal amplifiers and repeaters are used at the splicing points or at other necessary sites. There are no power problems, the design of the fiber optic cable implies the ability to transfer current from which the equipment placed at a distance of up to 150 km from each other is powered.
Here is what a signal amplifier looks like before installation, in partial parsing:
And so it looks ready to be laid at the bottom of the ocean:
But what to do if it is too early to install the repeater and the cable bay is over?
As mentioned above, repeaters, depending on the properties of the cable and the circumstances of installation, can be mounted with a frequency of up to 150 km. Modern industry allows the manufacture and delivery of cables with an average length of 5 and sometimes 25 km, which is significantly less than the distance of the repeaters. In these cases, the end of one coil is spliced ​​with a new one, and the junction is protected by a so-called docking box (see the example of such a construction below):
Box parsed:
In turn, repairing, for example, a break in an already laid cable is not a simple matter, although the procedure itself is schematically very banal. With the help of the vessel, one ragged end is lifted to the surface and fixed to the buoy, then the second end of the cable is also pulled up and lifted. The part into which water has penetrated under pressure is cut off, and to connect the ends, use repair cable “trimming”, specially reserved for this. In general, everything looks simple and logical: cut, trimmed, twisted, works. But the scale of such a “twist” is amazing, and it has little relation to the installation itself. If you're lucky, I can talk about this procedure separately.
I hope you enjoyed this material.
Source: https://habr.com/ru/post/242381/
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