Very cold winters sufficiently severe to cause widespread damage to road foundations occur infrequently in Great Britain. A design procedure for new roads has been adopted which minimises the danger of frost-damage to subgrades by ensuring that the materials used in the construction of the road are not susceptible to frost-heave. Consequently, frost-susceptible materials are banned from the top 450 mm of construction throughout Great Britain. This approach relies on the assumption that for design purposes road pavements may be regarded as being at equal risk to frost penetration. This report describes a study of meteorological records for various sites (from Cornwall to the Scottish Highlands) during the period 1959-1981. The frequency and severity of cold spells were examined with regard to the risk of frost penetrating deeply into a road. The results show that the present assumption of equal frost-penetration risk is untenable. Consideration should be given to reducing the thickness of non-susceptible construction required at a given site (with consequent economic benefits) on the basis of an examination of the meteorological records for the locality. Some further investigation is needed, because, in addition to finding the frequency of cold spells, the way in which successive spells combine to influence frost penetration must be taken into account.

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