National Highways update CD 534 to V0.1.0
A GUIDE TO NATIONAL HIGHWAYS CD 534 V0.1.0
National Highways has updated a significant set of its requirements for manhole covers and gully grates installed on the road network, for which it is responsible. The document in question is CD 534, which was first released in February 2020 and has now been updated to version 0.1.0.
CD 534 initially replaced HA 104/09 and forms part of the National Highways Design Manual for Roads and Bridges (DMRB). CD 534 equally applies to the network managed by Transport for Scotland.
You can get a quick overview of the essential updates to note below:
Frame bedding pressure on chamber walls
CD 534 recognises that load transfer from the frame to the underlying bedding material is an important factor in determining the lifetime of an installation. To ensure that an adequate area is provided to spread the load, without overstressing the bedding material, CD 534 sets a minimum flange area for all 600x600mm and 675x675mm manhole cover frames. The required minimum frame flange areas are shown in the table below:
As with HA 104/09, these minimum flange areas equate to the ‘nominal bearing pressure’ of 2.1N/mm². This was omitted from the first version of CD 534. Nominal bearing pressure is calculated by dividing the 400kN (D400) or 600kN (E600) test load by the flange area.
All Wrekin Highway and Unite ranges comply with this requirement.
To ensure frames are stiff enough to resist the loads involved, in this latest version of CD 534, a lower limit of frame mass has been specified for all 600x600mm and 675x675mm manhole cover frames.
All Wrekin Highway and Unite frames satisfy this requirement.
A frame depth of 150mm is now required on all installations on motorways and all-purpose trunk roads.
All Wrekin Highway and Unite ranges are available with 150mm frame depth options.
Testing of skid resistance
CD 534 now stipulates only one type of test for covers with raised chequer. Previously it could be satisfied with the conventional pendulum test, which measures the resistance caused to a swinging ‘shoe’ by the cover surface, or the more recent WRc test, which measures a small tyre’s resistance to sideways slip caused by the cover surface.
It is now mandatory to demonstrate compliance with the WRc test. All manhole covers with the Wrekin triangular or Unite chequer satisfy these requirements of CD 534. This means all Wrekin Highway and Unite ranges comply with the requirement.
All busy roads on the National Highways network require E600 rated manhole covers. This does not affect gully grates which are required to be D400.
The key method to identify if the road is sufficiently busy is to look at the number of light goods vehicles using that section of road. This data can be found on the Department for Transport website. Each count point has its own webpage on which you can find the number of light goods vehicles using that stretch of road. If this figure is over 1,500, then any new manhole cover will have to be E600.
Within CD 534, there is also a new note for specifiers and contractors, in which the need for access covers to be sited in carriageways has been removed. This may reduce the demand for some carriageway covers, instead requiring lighter duty assemblies for positioning in the verge or pedestrian areas.