A DESIGN FOR PAVEMENTS TO CARRY VERY HEAVY TRAFFIC --PROCEEDINGS OF THE FIFTH INTERNATIONAL CONFERENCE ON THE STRUCTURAL DESIGN OF ASPHALT PAVEMENTS HELD DEFLT UNIVERSITY OF TECHNOLOGY, AUGUST 23-26 1982. VOL 1 AND 2. -- NETHERLANDS

In the United Kingdom standards for the structural design of road pavements are based largely on results obtained from full-scale experiments. Over the 30 years that many of these experiments have been in existence, comprehensive data have been obtained on their performance. However, there remain serious shortcomings in their use to develop a comprehensive set of design standards. In particular, it is difficult to design roads to carry traffic much greater than the traffic levels accumulated by the full-scale experiments themselves and, because of the recent marked increase in the damaging effect of traffic on the most heavily trafficked roads, there is now an urgent requirement for designs well beyond the proven range of present design recommendations. This paper described how this need has been met by the development of an interim design in fully flexible construction from the best current information from mechanistic models combined with that from full-scale road experiments and performance testing. Fatigue cracking, although not usually the first cause of deterioration of fully flexible pavements in the UK is important, particularly on the more heavily trafficked roads, because of the consequent need to reconstruct both surfacing and roadbase of a cracked pavement. A computer model of the pavement structure has been developed to predict fatigue performance taking into account variations in pavement temperature and wheel-load spectra. The model has been calibrated by testing a pavement under controlled conditions in a pilot scale test facility and then validated by comparison with the fatigue behaviour of full-scale pavements of known performance. To ensure adequate resistance to deformation, the deformation behaviour of pavements to carry heavy traffic has been examined in relation to that determined from full-scale and laboratory experiments. Linear elastic analysis was used to demonstrate that vertical stresses in the soil under traffic were not excessive. This approach has been used to formulate novel designs for roads carrying very heavy traffic, cumulative traffic in excess of 80 million equivalent standard 80 kn axles over a 20 year design life. The design consists of a thick course of well compacted coated macadam placed between layers of rolled asphalt wearing course and lower roadbase. This construction combines the deformation resistance of dense coated macadam with the good fatigue properties of rolled asphalt. Such a design was first adopted for the reconstruction in 1979 of a section of the m6 motorway, where the new 20 year design life was 160 msa. Structural properties of pavement components and of the subgrade were checked during reconstruction and the performance of the pavement has shown the design to be soundly based.(a) for the covering abstract of the conference see IRRD 815640.