In the article ‘Main laying methods of communication cables’, the direct burial, overhead, and pipeline laying methods are introduced, this article will continue introducing other common installation methods include: laying in high-speed rail ducts, underwater laying, wall laying, leading up, indoor laying, etc.
1 Laying of optical cables in the high-speed railway channel
The laying of optical cables along high-speed railway lines not only has low construction difficulty and high safety, but also shortens the relay distance and reduces transmission delay for communication trunk lines. In recent years, the construction of trunk optical cables along high-speed railway lines has become increasingly common.
The high-speed railway line itself has the demand for electricity and communication. Strong and weak current channels are set up on both sides of the rail, and communication optical cables are laid in the weak current channels, as shown in Figure 1.
Due to the limitation of the cross-sectional size of the weak current channel, optical cables are generally laid in an S-shape inside the channel for residual use, as shown in Figure 2. Leave a gap on both sides of the fiber optic cable joint and every 500 meters or so.
High speed railways are usually constructed in an elevated manner, and communication cables need to be laid through bridge piers when leading out of the railway, as shown in Figure 3.
The type of optical cable laid through the weak current channel of high-speed rail is usually GYTA58. This type of cable has the same structure as GYTA53 cable, but the outer layer of the cable uses low smoke halogen-free flame-retardant polyolefin (the outer layer of GYTA53 cable is polyethylene), so the optical cable has certain flame-retardant properties.
2. Underwater fiber optic cable laying
Directly buried cables usually need to be laid underwater when passing through ditches, rivers, and ponds with water. The underwater mentioned in this article does not include lakes, oceans, large rivers, and other underwater areas with long distances from the water surface. The laying of optical cables on the corresponding underwater areas can refer to the relevant content of submarine cable laying.
The laying methods of underwater cables mainly include: interception and trenching, water pump flushing, and directional drilling.
2.1 River interception and trenching
To intercept and dig trenches, it is necessary to first cut off the water in the ditch and river with a dam, and then drain the water in the section where the fiber optic cable trench needs to be excavated. After that, subsequent operations such as digging the cable trench can be carried out, as shown in Figure 4. The water blocking dam can be temporarily stacked with woven bags filled with soil. When the water is deep, the dam can be reinforced with logs (raw wood). When the water in ditches and rivers is flowing, it is usually only necessary to intercept it upstream of the cable trench. The unit length cost of intercepting, digging trenches, and laying cables is usually high.
2.2 Water pump flushing tank
Water pump flushing usually requires divers to carry equipment for underwater construction. Divers first use high-pressure water guns to create a trench about 1.5 meters deep underwater, then place plastic pipes inside the trench and press them onto the bottom with cement mortar bags. The length of the plastic pipe needs to cross the entire water surface, which is equivalent to building a section of plastic pipe underwater, as shown in Figure 5. The optical cable is laid through the plastic pipe.
During the construction process, it is not easy to sink the plastic pipe into the water due to the presence of air inside. Figure 6 shows the construction site of the water pump flushing groove in a certain project, with a cement mortar bag in the lower left corner of the picture. Due to the fact that water pump flushing tanks are mainly constructed underwater, the construction difficulty is high and the construction quality is often difficult to guarantee. Therefore, they are currently rarely used.
2.3 Directional drilling
When using directional drilling to lay underwater cables, the drilling rig first drills guide holes at the bottom of the riverbed. The depth of the guide hole from the bottom of the riverbed is generally not less than 3.0 meters. After the guide drill bit is excavated at the predetermined position, remove the guide drill bit, replace it with an expander to enlarge the guide hole, and pull back the plastic pipe. The process of directional drilling and pipe laying is shown in Figure 7. After the plastic pipe is laid, the optical cable is then laid through the plastic pipe.
Directional drilling is currently the main method for laying underwater cables, and a small drilling rig can lay up to a maximum length of 300 meters.
3 Cable Installation on wall
In old residential areas without communication pipelines, optical cables are mainly laid through the walls of buildings. There are two main ways to lay wall fiber optic cables: hanging wire type and nail fixed type.
The hanging type fiber optic cable is attached to the wall through steel strands installed on the wall, as shown in Figure 8. One steel strand can attach multiple fiber optic cables. Steel strands are fixed to walls using iron fittings. Common iron fittings can be found in the article “What are the main iron fittings for hanging wire wall optical cables”.
The straight section of the cable is often fixed by nailing when the laying distance is short (generally less than 10 meters), as shown in the lower left corner of Figure 8. Fiber optic cables are generally fixed with steel nail clips, with each clip securing one fiber optic cable.
4 Fiber optic cable lead up
When optical cables are switched from underground laying methods (direct burial, pipelines) to above ground laying methods (overhead, walls), they usually need to be led up. The point where the optical cable is led up is usually against a pole or wall. The part of the optical cable that is within 2 meters above the ground usually needs to be protected with steel or plastic pipes, as shown in Figure 9.
Some people also refer to “leading up” as “leading down“, but “leading up” is the proper noun!
5 Indoor fiber optic cable laying
Fiber optic cables laid indoors are relatively easy to see, similar to the laying method of other indoor cables. Indoor fiber optic cables are mainly laid through cable trays and trunking, as shown on the left in Figure 10, or laid inside the ceiling.
Indoor cables should use flame-retardant cables. After passing through holes in floors and walls, fireproof sealing materials should be used to tightly seal the holes, as shown on the right in Figure 10.
6. Shallow burial of optical cables
According to existing regulations, buried cables should be used for direct burial, and the burial depth in ordinary soil should exceed 1.2 meters. This standard is neither necessary nor practical for accessing cables, especially for peripheral access cables. In practical engineering, shallow burial is often used for the installation of fiber optic cables at the end, that is, ordinary fiber optic cables are protected by plastic pipes and buried at a distance of 0.2-0.3 meters from the ground surface under sidewalks or green belts, as shown in Figure 11.
In real life, we often see situations where cables are shallowly buried, such as the wires of street lamps and video surveillance cables. Becuase the strong cable lines can still be shallowly buried, why not of the access cable?
Yingda suggest that shallow burial should be allowed for access cable and corresponding regulations should be formulated. The burial depth and protection measures should be specified according to the importance of the optical cable and the location of burial.
Except above common laying methods of communication cables, there are some specific types of optical cables may also be used and special laying methods may be adopted, such as road micro groove optical cables, rainwater pipeline cables, etc. If you are interested, welcome subscriber with us, will update from time to time.
