INNOVATION AND FLEXIBILITY
THE
INSTALLATION AND MAINTENANCE TRAINING MANUAL
3.8.3 Informative Guide to Correct Duct or Conduit Placement (UK experience)
Preparation
Where the trench base is considered unsuitable for direct installation of the conduit a protective layer of suitable material (chosen from
the NRSWA spec, appendix A1) should be installed. Bedding must be uniformly graded to provide continuous support.
Under no circumstances should blocking or mounding be used to raise to conduit grade.
Where an unstable trench bottom is encountered it must be stabilized before laying conduit. This over-excavation is then replaced with
a bedding of crushed stone or gravel to provide a high density stable base. This material should be graded to act as an impervious mat
through which the unstable soil will not penetrate. (Suitable materials are identified in Appendix A1 of the NRSWA spec).
In addition, the following should be noted:
a. Proper conduit bedding
To ensure a proper bed for the conduit, the trench bottom should be level, well compacted and free of loose soil or rocks.
b. Width of trench
The width is determined by the number of conduits laid side by side plus any required spacing between conduits and the trench walls.
Further guidance from the conduit manufacturer should be sought on minimum values which shall be maintained throughout the
trench.
c. Changes of Direction
Avoid unnecessary turns, or changes in level and direction. Keep changes in direction as gradual as possible to assure ease of cable
installation. In general maintain a grade or direction change of no more than 10:1 – one metre of length change for each 100mm of
elevation or direction change. Advice should be sought from the conduit or cable manufacturers on pulling and bending radii which
must be taken into account when planning the route.
Placing Multiple Conduits
Where multiple conduits are installed, these should be placed in separate layers with the spacing in accordance with advice below.
Separation of Conduits
Once all the conduits in the bottom layer have been laid and properly aligned, they should be secured in place by suitable means to
prevent movement during backfilling.
Conduits that touch vertically may be structurally unstable. Reference should be made to the manufacturer for advice. Unless otherwise
specified a minimum of 25mm separation should be maintained between the conduits vertically and 50mm between the outside conduits
and the sides of the trench. Backfill material in accordance with NRSWA spec shall be placed over and around the layer of conduits, care
being taken to ensure that all voids above, below and around the individual conduits are properly filled.
This procedure should be continued until each of the layers has been properly placed in position and surrounded. The final levelling of
the surrounding materials should be checked to ensure that the correct thickness has been maintained throughout.
Surround to Conduits
Material details and installation procedures for the surround material to conduit shall be the responsibility of the relevant undertaker,
subject to the following overall requirements:
(1) Class unacceptable material and materials that contain particles greater than 38mm nominal size (1.5”) shall not be used.
(2) Fine fill materials may be laid to a max of 250mm above the top of the conduit and shall be properly compacted and must offer
adequate support for the remainder of the reinstatement, and shall be capable of transmitting the imposed loading to the subgrade
below the conduit.
3 Outdoor Installation
“This document is intended as a guide only. Whilst the information it contains is believed to be correct, Emtelle can take no responsibility for actions taken based on the information contained in this document. Emtelle reserves the
right to make changes to this document without notice. All sales of product are subject to Emtelle’s terms and conditions of sale only, which can be found on Emtelle’s website.”
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INNOVATION AND FLEXIBILITY
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