Flexible pavements

Abstract

The ‘Laboratório Nacional de Engenharia Civil — LNEC’ (Portugal), the ‘University of Nottingham — UNott’ (United Kingdom), the ‘Laboratoire Central des Ponts et Chaussées — LCPC’ (France) and the ‘Delft University of Technology — TUD’ (Netherlands) were awarded a laboratory twinning project under the ‘SCIENCE’ program of the European Community — DG XII, entitled ‘A European Approach to Road Pavement Design’, contract no. SCI 01 30-C (SMA). The purpose of this Symposium will be the presentation of both the results obtained during this project (papers of the Science program), and other selected relevant research that contributes to a European approach to road pavement design (papers outside the Science program). AIMS OF THE SCIENCE PROJECT The enormous increase of heavy traffic on roads, the need to economically use local materials and the availability of new road construction techniques all require the development of more effective pavement design methods than are available using current empirical techniques. Such methods require a rational study of the mechanical behaviour of the constituent materiais and sou, more rigorous structural analysis, and appropriate analysis to match the actual pavement behaviout The construction and maintenance of flexible pavements of light and moderately trafficked roads in Europe and in developing countries are often uneconomical owing to defective understanding of the mechanical properties of pavement materiais and foundation soils. This may lead to either overdesign, or underdesign and hence to early failure of the pavement. As the European Community member countries are the largest importers of bitumen in the world, improved knowledge about unbound granular materiais and sou subgrade will provide a marked reduction in the construction and maintenance cost of bituminous pavements. In Europe there is a need for cooperation between different laboratories in this work. This Science project aims to coordinate and harmonize the activities of the different laboratories working in this field. The reliability of a structural method of road design depends on a mathematical model and on the quality of data with respect to the mechanical properties of the pavement materiais and subgrade. Such properties (resilient and plastic) need to be detennined by laboratory means and this has traditionally been through cyclic loading triaxial tests that can closely simuiate structure. The suitability and/or limitations of the testing approach require investigation as the reliability of the pavement design depends upon it. THE SYMPOSIUM The Symposium embraced a wide scope of experimental and analytical research with respect to foundation and pavement design. For this purpose the Symposium has been divided nito five sessions: Sessions 1 and 2 have been devoted to the experimental detennination and mathematical modelling of stress-strain behaviour of subgrade soils and unbound granular materiais; Sessions 3 and 4 covered the non-linear pavement analysis and the pavement design. An emphasis is done to the harmonization of experimental methods. In addition to these sessions related with the Science program a Session 5 about monitoring and performance of flexible pavements was inciuded, which contains only papers outside the Science program. These contributions wili greatly assist with the worldwide improvement iii standards for testing subgrade soils and unbound granular materiais and for flexible pavement design. The future chailenge will be implementing this experience to a larger cooperation between European research organizations.