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Underground Duct Installation Details

Underground Duct Installation Details : Many types of underground ducts are installed but I will only discuss the duct installed in the telecommunication with the safety purpose of Optical Fiber Cable. Before installing the duct on the proposed route, our duct drawing has to be understood very well and get information about other utilities coming in that route. Achieving depth is the first objective in duct installation. The depth of installation, (or required "cover") shall always be measured to the top of the installation.

For parallel installation of duct between telephone and power cables, the proper separations among them are mandatory. For the installation of duct safety on site is also very necessary like- warning signs, fencing, traffic barriers, accesses etc., shall be provided and maintained so as to safeguard and cause minimum inconvenience to the public. For the strong safety purpose flashing amber warning lights mandatory at night.
Underground Duct Installation Details

General Installation Details for Duct

For the installation of telecommunication duct the line and level of the duct formation shall be kept as straight as possible. Bends will be required for duct formations to be routed around corners at intersecting roads. (If Manholes or Handholes required than for safety reasons manholes shall usually be planned and located away from intersections).

Duct installer should always try to duct installation in the presence of site supervisor, duct laying shall not be done in the absence of the site supervisor unless prior permission has been received.

All ducts shall be located in accordance with company standards. In the absence of approved company  standards, the Technical Department of the Telecom Industry must be consulted to ensure compliance with the appropriate standard which may vary depending upon the nature of the undertaking.

When duct routes  constructed in the vicinity of electrical plant, according to company guideline it will be compulsory to follow the process of isolation. As far as is practicable, underground ducts joints or between manholes ducts joints shall be watertight . A PVC solvent shall be used  for the watertight purpose. Underground duct installation methods shall prevent sand and soil from entering the ducts.

Duct interchange is found in the manholes in the underground duct installation, care should be taken before to avoid the duct interchange. This problem is always seen in the Telecom Underground duct, which is a big problem for the O&M department.

The base of the underground duct should not be more than 20 cm bumpy, otherwise the chances of getting kink in the duct increases. The underground duct formation may be curved to approximately 90°. The cold bending radius for PVC duct shall not be less than 12 meter. Preformed bends and/or 5° couplings shall be used where smaller radius is required. 

Underground duct in  concrete

The method of underground duct installation shall ensure that the standard spacing is maintained and that all space between the ducts and a minimum of 75-mm surrounding the ducts is filled with concrete. The distance between the ducts shall be 30-mm. Duct spacers which is used for the separation of underground ducts shall be used every 2.0-m along the duct line to position the ducts.

Use concrete vibrator-pokers- shall be of 30-mm maximum OD, and shall only be used in the 75mm plus space between the ductwork and the sides of the excavation. If underground ducts are installed with less than a 400-mm depth of cover, as may occur with a road crossing, the concrete formation shall be increased by an additional 100-mm thickness of R/C slab.
Underground duct in  concrete

Underground duct in sand or normal soil

The sand or normal soil shall be compressed between each layer and there shall be a minimum covering of 10 cm of sand. It should be maintained minimum covering above upper duct layer shall be 100-cm. The separation of underground ducts  either longitudinal or perpendicular, to other services, should be 150-mm. Where this is not possible, it is necessary to separate / maintain a 50 mm layer of concrete.

The underground duct installation shall be covered with 100-mm of sand. This is to be followed by approximately 200-mm suitable backfill and a plastic warning tape. Warning tape shall be used all over the underground duct route.

Underground Sub-ducts

Underground sub-ducts shall be installed, If possible possible the continuous length between manholes. Only one joint may be permitted in a length of underground sub-duct. The joints produce the minimum interference with the installation procedures of both the sub-duct, subsequent cabling, and possible future additions of sub-ducts if the first installation does not consist of the full complement. More joints make more problems and during the installation of suc-duct and cable pulling typical forces need to applied.

Before the installation of  sub-duct it should be mandreled and cleaned prior. After installations of underground sub-duct shall be mandrel tested and sealed with end-caps. The rope used in sub-duct shall be tested for necessary strength for pulling of the cable hauling wire.

Last Word

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