An anisotropic model of unbound granular material under repeated loading

The base and subbase layers of a pavement are compacted to the desired density by rollers. This cause the anisotropy in other words the layer more stiffer in the vertical direction than the horizontal direction. In the study inherent and stress induced anisotropy were measured by using the repeated load triaxial test equipment which is able to cycle both confining and axial pressure. The test results were then modelled using the stepwise regression. A new cross anisotropic model was proposed to predict the unbound stress-strain behavior. The proposed model is able to predict the axial strain more accurately than the radial strain.

European Research into Granular Material for Pavement Bases and Subbases

Two transnational European research projects in the area of granular materials for road pavements are described. The results are used to illustrate the state of practice as compared to the state of the art and are placed within the setting of a broad picture of national research within Europe. Discussed are the direction of European research, its implementation, those areas that will continue to be problematic, and the findings and strategies that suggest better-practice for non-European users. The use of the repeated-load triaxial test is shown to be an important aspect. Although the test is shown to have limitations for practical purposes, it illustrates the nature of material behavior that may be expected in situ. It is shown that a fundamental engineering understanding has been applied to granular material pavement layer technology but that there remain issues of in situ assessment, analytical methods, and variability of in situ conditions that hinder full application of current understanding.

Characterization of granular materials for pavements

For design and analysis of flexible pavements, a simple elastic model that does not require cumbersome calculation and also can rank materials according to their performance is clearly desirable. Early studies indicated that the resilient modulus of a granular material can be taken to be a function of the first invariant of stress, θ, although there is evidence that it is also dependent on the repeated deviator stress, qr. The limitations of some earlier models are discussed herein and a simple model for granular materials is proposed. The model is empirical in nature and based on repeated load triaxial testing with constant confining pressure. The application of this model in situations where the confining pressure is pulsed in phase with the deviator stress is also discussed. Key words: repeated load, triaxial test, resilient modulus, granular materials, modelling, pavement.