THE TRRL METHOD FOR PLANNING AND DESIGN OF STRUCTURAL MAINTENANCE --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

Effective use of the large sums of money now being spent world wide on strengthening roads requires a design system capable of matching spending to needs; it should establish priorities for work and also the nature and extent of strengthening on the roads selected for treatment. Economical solutions can generally be obtained if a relatively thick overlay is applied before the structural integrity of the road pavement is seriously impaired, when the road is in a critical and not a failed condition. The transport and Road Research Laboratory has therefore developed a method for the planning of structural strengthening that can predict the remaining life of the pavement so that the strengthening can be timed to coincide with the onset of critical conditions; the method can also design the necessary thickness of overlay required to extend the life of a road to carry the predicted future traffic. Papers to previous conferences have described earlier stages in the development of the method from a systematic study of the relation between the deflection under a loaded wheel and the performance of pavements in the laboratory's many full-scale road experiments; the work has been supported by detailed observations of the deflection behaviour of pilot-scale pavements and by analytical techniques. This paper outlines the method concentrating on the latest work to complete its development, evidence of its validty and examples of its use. Extensive experimental data is presented that has been used to develop charts relating deflection to pavement temperature so that deflections measured over a range of temperatures on different pavements can be corrected to equivalent design deflections at a standard temperature of 20 deg c. The development of pavement deterioration and its relation to deflection levels is illustrated, in particular the increasing uncertainty as pavement failure approaches, uncertainty that may be avoided by suitable definition of critical conditions and timely maintenance intervention. Typical evidence is presented defining experimental relations between deflection and critical life. The information has been consolidated into design charts for the prediction of remaining pavement life to the onset of critical conditions; separate design charts have been produced for the four main types of road base used in the United Kingdom. Measurements on a number of in-service pavements demonstrate the validity of the charts over a wide range of traffic. Observations of the reduction in deflection achieved by different types of overlay material are presented. These results have been combined with information on the performance of overlaid pavements to produce overlay design charts. Levels of probability of achieving a particular residual life or, in the case of an overlay, an extension of life are defined on the design charts. Maintenance decisions based primarily on deflection but supported by other information have been made on many