this report describes an experiment on sevenoaks by-pass (a21) to investigate the performance of a fully flexible road, the road base and base-course of which were constructed in 4 different configurations of thickness of gravel asphalt. the performance was assessed in terms of degree of compaction achieved, surface irregularity and the accuracy of surface levels of the bituminous pavement layers. an attempt was also made to investigate the performance of different types of roller on thicklift construction. the background to the general practice of laying bituminous materials in relatively thin lifts in the united kingdom is first described and this is followed by a summary of early trials of thick-lift construction made in this country. the results obtained in the experiment at sevenoaks by-pass showed that for the particular material and thickness used in the experiment the most attractive form of construction would be a single lift of 175 mm under a basecourse 60 mm thick. further studies are proposed before construction of bituminous materials in thick lifts may be advocated for general use. (a).

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