Application of soil mechanics principles to the design of pavement foundations, the design of complete pavements and to their structural evaluation'in-service' has lagged some way behind knowledge accumulated through research. Present design methods are generally empirical and often based on use of the California Bearing Ratio test, which was abandoned in California some fifty years ago. The soil mechanics problem is one of understanding how soils and granular materials respond to repeated loading and applying this knowledge to pavement design with the aid of appropriate theoretical analysis and an understanding of failure mechanisms. Non-linear stress-strain characteristics are a particular feature of the problem and have to be catered for in design and evaluation. Various ‘tools’ are available to assist the pavement engineer. These include theoretical analysis, laboratory testing apparatus, field testing and full-scale trials with appropriate instrumentation. The resilient and permanent strain response of clays and granular materials is reviewed in the context of the requirements for design. The essentially empirical UK Highways Agency method of design and its evolution are discussed in the light of current soil mechanics knowledge. By contrast, the development of mechanistically based approaches is outlined, together with suggestions for the implementation of present knowledge in a practical method of design for pavement foundations. Parallels are drawn between road and rail track design and developments relating to the latter are also reviewed. A forward look suggests that further research to improve understanding of the effective stress state below pavements and the application of recent theoretical work on partially saturated soils could form the basis for improved pavement engineering in the future. L'application des principes de la mécanique des sols à la conception des couches de fondation et de chaussées end&grav;res ainsi qu'à l'évaluation structurale des chaussées en service a un certain retard sur l;état actuel des connaissances. Les méthodes de conception actuelles tendent àêtre empiriques et reposent souvent sur l'essai de portance californien, que la Californie ellemême n'utilise plus depuis une cinquantaine d'années. Le défi qui se pose à la mécanique des sols est de comprendre la réaction des sols et des matériaux granulairesà des charges répé tées et d'appliquer les leçons qu'on en tire à la conception des chaussées en s'appuyant sur une analyse théorique judicieuse et sur la compré hension des mécanismes de rupture. Un aspect particulier de cette question est les caractéristiques de tension-déformation non linéaires, dont il faut tenir compte dans la conception et l'évaluation. L'ingénieur des chaussées dispose à cette fin d'une panoplie d'outils: analyse théorique, essais en laboratoire, essais sur le terrain et essais en vraie grandeur sur chaussées instrumentées. On examine ici les déformations élastiques et permanentes d'argiles et de matériaux granulaires dans le contexte des critères de conception. On analyse aussi la méthode de conception, essentiellement empirique, utilisée par l'administration routière du Royaume-Uni (UK Highways Agency), ainsi que son évolution, à la lumière de ce que l'on sait actuellement sur la mécanique des sols. Par opposition, l'exposé décrit brièvement les méthodes mécanistes qui ont été formulées et préconise l'application des connaissances actuelles dans une méthode pratique de conception des couches de fondation. II compare la conception des routes et celle des voies ferrées et examine les progrès réalisés dans ce dernier domaine. Pour ce qui est de l'avenir, le génie routier aurait fort à gagner de recherches plus poussées sur les tensions efficaces dans le sous-sol, ainsi que de l'application de récents travaux théoriques sur des sols partiellement saturés. Application of soil mechanics principles to the design of pavement foundations, the design of complete pavements and to their structural evaluation'in-service' has lagged some way behind knowledge accumulated through research. Present design methods are generally empirical and often based on use of the California Bearing Ratio test, which was abandoned in California some fifty years ago. The soil mechanics problem is one of understanding how soils and granular materials respond to repeated loading and applying this knowledge to pavement design with the aid of appropriate theoretical analysis and an understanding of failure mechanisms. Non-linear stress-strain characteristics are a particular feature of the problem and have to be catered for in design and evaluation. Various ‘tools’ are available to assist the pavement engineer. These include theoretical analysis, laboratory testing apparatus, field testing and full-scale trials with appropriate instrumentation. The resilient and permanent strain response of clays and granular materials is reviewed in the context of the requirements for design. The essentially empirical UK Highways Agency method of design and its evolution are discussed in the light of current soil mechanics knowledge. By contrast, the development of mechanistically based approaches is outlined, together with suggestions for the implementation of present knowledge in a practical method of design for pavement foundations. Parallels are drawn between road and rail track design and developments relating to the latter are also reviewed. A forward look suggests that...