The method of preparing the micro trench for installation is similar to the method of laying the cable directly into the ground, with the exception of micro trench dimensions. For channel laying, a micro trench is made with a width of 100 mm and a depth of about 250 mm. 1-2 channels are laid in it, containing up to 7 subchannels for laying cables: one central and 7 peripheral. The inner diameter of the channels is 10 mm. After laying the channels, the micro trench is poured with light concrete, and then the asphalt surface is restored. To locate the couplings and the technological stock of fiber-optic cable, special micro-wells are arranged, which are plastic or metal boxes buried in the ground and embedded in the asphalt. The neck of the micro-well is closed with a lid or hatch with a lock preventing unauthorized access. The entry of channels with cables is carried out through the walls with subsequent sealing of the entry point. The coupling is fixed to the micro-well wall, and the technological supply of the cable is laid out in the form of figure eight. Due to the small outer diameter of the cable, the minimum allowable bending radius of the cable is about 150 mm.
Cross-section of micro trans with a laid cable
The construction of traditional cable duct inspection devices involves a significant amount of excavation, including digging a pit, removing excess soil, tamping the soil at the bottom of the pit to avoid subsidence under the weight of the reinforced concrete structure. During construction, equipment is also necessary for unloading reinforced concrete elements of the well.
Since the microwells are located on the soil surface, and their size and weight are much smaller than standard viewing devices for cable ducts, much lower construction costs are required. First of all, this is achieved due to a significant reduction in the volume of earthwork, as well as by reducing labor costs.
For this technique, special micro cables have been developed, which are typical loose tube construction cables, but with optical modules of reduced diameter. Thanks to the use of such technological solutions and the improvement of cable materials, it was possible to reduce the outer diameter of the cable to 7.2 mm without reducing mechanical strength, that is, resistance to tensile and crushing forces, impact, torsion, bending, and also to temperature fluctuations. Such a cable contains up to 6 optical modules, each of which can have up to 12 optical fibers. Thus, the total number of optical fibers in a cable can reach 72. Modifications of these cables are also available, containing 8 and 12 optical modules and, respectively, 96 and 144 optical fibers.
Since the bulk of underground utilities is located in sewers and sewers that are at a depth of at least 1 m, and the depth of the microtrench is much less, the likelihood of damage to third-party utilities during installation is significantly reduced. The process of coordination of construction work at the design stage is also simplified.
Using standard methods for the construction of cable ducts, the installation speed is up to 300 m per day. The use of microtrench technology allows to increase the speed of construction up to several kilometers per day, without taking into account the time for the construction of viewing devices, where the advantages of this method are even more obvious.
As a result of the installation of one channel, it is possible to obtain cable ducts, ready for laying fiber-optic cables with a capacity of up to five hundred optical fibers.
Prospects
The broad prospects for the use of microtrench technology for laying fiber optic cables are due to the lack of the need to purchase additional expensive equipment and to attract foreign specialists to set it up and train staff. The road construction equipment necessary for the implementation of this method is available at road maintenance facilities. The advantage of this laying technology is the absence of the need for long breaks in traffic. In the case of work on streets with a slight traffic flow, traffic can generally not be blocked even in the case of a crossroads.
In conclusion, it should be noted that microtrench technology for laying fiber optic cables is much cheaper than traditional methods of building cable ducts. The application of this technique can significantly reduce labor costs and time for construction work, as well as improve labor efficiency through mechanization. The widespread adoption of microtrench technology in practice will intensify the development of the inter-station network in megacities and thereby improve the quality of customer service.
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