ASSESSMENT OF PAVEMENT FOUNDATIONS DURING CONSTRUCTION

The construction of road pavement foundations in the UK has traditiona lly been carried out according to 'recipe specifications', by which ap propriate (graded) materials are laid by appropriate procedures to pro duce a material with (at least) an adequate performance. This has inev itably resulted in roads that are, in some cases heavily, overdesigned . This type of specification, however, provides no information on, and thus no assurance of, the performance of the 'as constructed' materia l layers. In addition, marginal, often locally derived, and hence chea per, materials are often excluded from use, and there is no facility f or efficiency in construction operations, such as reduction in compact ive effort. 'End product' testing would remove this limitation, hut in order that this can be introduced two requirements must be met (a) pe rformance criteria must be isolated and set (b) a suitable test or tes ts must be found to measure accurately the performance criteria of the 'as constructed' layers in situ. This paper discusses the relevant pe rformance criteria and recommends appropriate values. The tests that a re both currently available and are being developed, both in the UK an d overseas, for determining the relevant parameters from performance t esting in situ are reviewed and are analysed in terms of the stress le vels applied, duration of the stress pulse, and the precision, accurac y and relevance of the output. The practicality of the tests is also a ssessed. Recommendations are made for the adoption of 'end product' te sting and of research and development necessary to introduce such a sp ecification successfully.