The duct access chamber shall be constructed from 49mm wide, high strength, High Density Polyethylene and be black in colour. It should be constructed using separate 150mm deep interlocking sections. These shall be made up to the required depth.
The chambers should be bedded on a base of 100mm thick C20 dry mix concrete and the base should be chamfered to obtain a natural soakaway outlet. Plastech are also able to offer a range of pre-fabricated, manhole base units, which will considerably speed up the installation process and give a more aesthetically pleasing finish.
The duct access chambers have been designed to be a free standing, load bearing chamber and are not reliant on having a concrete surround. Depending on the site location, it is possible to use the following back fill media.
As Dug Material
In order to use as dug material for backfill purposes, the contractor must be satisfied that the material reaches the correct compaction values and must be free from sharp stones. As dug material is not recommended for areas where there is any possibility of being run over by vehicular traffic, as there is the possibility that the back fill would be disturbed and eventually cause the chamber to move and eventually fail.
Typical Areas Where As Dug Material Could Be Used
In areas of light pedestrian traffic and areas protected by a guard rail (road traffic island etc).
Imported Granular Material
If the native, as dug material is not suitable for use then imported granular material displaying the correct compaction values, should be placed around the chamber instead and compacted.
The use of a 150mm concrete surround is also acceptable, but not always necessary. A concrete surround should always be used in areas of vehicular traffic to prevent the chamber from rocking. Unlike a lot of other systems on the market, our chambers will not buckle when surrounded with concrete.