Not All D400s Are Created Equal

Within our ductile iron manhole cover range Clark-Drain offers 3 types of D400 products. Each of these is intended for different applications but we are increasingly finding that the wrong type is chosen, with price often seemingly being the most influential factor.

A product compliant to EN124 D400 loading is merely making a statement about its static vertical loading capability under laboratory conditions, not that it is suitable for any location with any amount of road traffic. This is because in certain situations, such as roundabouts, road junctions, main roads, areas of high traffic density, etc., the dynamic loading effects exerted by vehicles passing over manhole covers either at high frequency and/or at speed means they are potentially subject to far greater stresses than other locations. This in turn can produce stress fatigue failures either in the manhole cover itself or more likely through the frame and to the bedding upon which it is sited. A product’s ability to resist a static vertical load of 400kN is only one small part of the equation of what goes into making a product suitable for a given application in terms of durability in service.

Ideally, we’d only offer one type of D400 cover in our range that was suitable for all locations, even if it was overkill for less demanding applications. However, in today’s cost-conscious market we have found the need to develop more competitively-priced products for those less demanding applications. Unfortunately we find that this leads to the wrong product being selected for the application on occasion, so to clarify:

  • Non-carriageway D400 products (e.g. CD 701 KMD, CD 1659 KMD, etc) = suitable for use in areas subjected to slow-moving vehicles only, including occasional HGV’s. Car-parks, cul-desacs, retail delivery areas, private access roads, etc. Not suitable for use in carriageways.
  • Carriageway D400 products (e.g. CD 701H KMD, CD 1659H KMD, etc) = suitable for use in carriageways subject to low-density traffic including HGV’s, fast or slow-moving.
  • Heavy-duty D400 products (e.g. CD 901H KMD, CD 902H KMD, etc) = suitable for use in carriageways subject to high-density traffic, fast or slow-moving.

Selection of the wrong product is likely to lead to an early failure of the manhole cover and/or bedding, meaning a costly on-site repair. A few pounds saved up front can therefore lead to great expense in the long run so if in doubt, always select the higher specification product.

Construction Sites

We are occasionally called to construction sites where D400 products have failed. Whilst the product chosen and installed may be appropriate for the long-term intended use of the road, the fact that during construction a number of large site vehicles, often carrying large and unusual loads, will pass over the products is overlooked in the planning and specifying stages. Again, the dynamic loadings that such vehicles exert are far greater than their static mass would suggest. Accepted best-practice is to protect any ironwork from trafficking until all construction is completed, and this is what we also recommend, but as further caution consideration should be given to installing either a higher specification of D400 product (see above) or even an E600 product to avoid failure should the product be unintentionally trafficked by site vehicles.

- Uploaded 08/10/2015