Laying cables in tunnels and collectors
A cable tunnel is a long, closed structure with supporting devices designed to accommodate cables and cable glands. It is a corridor-type room with the possibility of free passage along the entire length, which allows laying cables, as well as performing inspections and repairs of cable lines.
Tunnels with, in addition to cables, other communications (water supply and heating network) are called collectors. Such a neighborhood has a very favorable effect on the laid cables, since water pipes help to lower the temperature in the cable structure, and heat pipes reduce dampness.
It is recommended to build cable tunnels and collectors on the territory of cities and enterprises with dense development, with many underground utilities, as well as on the territories of large metallurgical, machine-building, and other energy-intensive industrial enterprises. This method is used, as a rule, when laying more than 20 cables in one direction.
Tunnels and collectors are constructed from reinforced concrete elements of round or rectangular cross-sections. Constructions of circular cross-section through passage, as a rule, are designed for double-sided cable laying, and rectangular structures can be used for both double-sided and one-sided cable laying. The latter are of through-passage and semi-through design, and if it is necessary to lay a large number of cables, they can also be three-walled (double).
Tunnels, like all cable structures, have certain requirements. So, the height of the passage between the cable structures should be at least 1.8 m, the width of the passage with two-sided placement of structures should be at least 1.0 m and with one-sided placement – at least 0.9 m. Underground tunnels outside buildings are buried in the soil at least at 0.5 m. And their floors are performed with a slope of at least 0.5% towards the water collectors or storm sewers.
The dimensions of the collector are determined depending on the number and type of communications placed in it, and its design is selected based on the method of construction. Collectors with a circular cross-section are usually built using shields and in a more closed way, and rectangular collectors – in an open way.
As protective measures in case of fire, cable tunnels are separated from other rooms and adjacent cable structures by partitions and ceilings made of non-combustible materials. And the tunnels themselves contain fire-resistant partitions at a distance of no more than 150 m.
The tunnels should have exits at their ends. Moreover, emergency exits should be equipped in the form of a hatch or built into overhead structures.
Tunnels and collectors are equipped with water collectors or storm sewers, natural or artificial ventilation systems, smoke sensors, means for remote and automatic fire extinguishing, electric lighting and a power supply network for portable lamps and tools, as well as automatic fire alarms.
Control over the air temperature in the collector, the operation of ventilation and pumping units, as well as other operating conditions of the structure, is carried out from the control center equipped with telephone communication, alarm and remote control.
To lay cables in tunnels and collectors, one uses support metal structures with an anti-corrosion coating are installed. The distance between structures must be at least 1 meter.
Usually, in a double-sided collector, pipelines are placed at the bottom on one side of the passage and communication cables are placed above them on brackets on top. On the other side of the passage, there are a water supply system and power cable lines are placed above it. In a one-sided collector, at the very bottom, there are water and heat pipelines, communication cables are laid above them on brackets, and power cables are laid at the very top. In this case, power cables and communication cables are separated by a horizontal partition.
The technology of laying cables in tunnels, their location and fastening to structures, as well as the execution of horizontal partitions and the installation of couplings are similar to laying in cable channels.
The laying of cables in collectors and tunnels is calculated in the way to provide the possibility of additional laying of at least 15% of the cables provided for by the project (replacement of cables during installation, additional laying for further operation, etc.).
Only cables with non-combustible sheaths may be used for laying in tunnels. Cables are rolled in tunnels and collectors using a winch or manually (with a cable length of up to 50 m), using rolling rollers. After that, the cable is manually laid on cable structures mounted along the walls.
The laying of cable lines in tunnels and collectors is considered one of the most reliable and durable underground systems. Its undeniable advantages include a high degree of line protection, as well as convenience and direct access for maintenance.
The disadvantages are high construction costs, insufficient hydro-tightness, and the risk of fire due to the high internal temperature of the tunnel.