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:
| Cover duty |
Minimum frame flange area (mm2) |
|---|
| D400 |
190,000 |
| E600 |
285,000 |
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.
