Strain and stress distributions in flexible pavements under moving loads

ABSTRACT Calculated strain distributions in flexible pavements were studied by comparison with measurements made on full-scale structures. The calculated results were obtained by elastic and viscoelastic modelling of these structures. As no stress measurements were collected, the stress distribution was studied by comparing the results of elastic and viscoelastic calculations. For different loading and temperature conditions, and assuming the hypothesis of the French design method for flexible pavements, modelling provided strain signals similar to those measured on real scale structures for strains at two different depths in the studied structures. This first conclusion was used to validate the models, which were then used in the stress study. Some unexpected strains variations were observed near to the surface of the structures. Modelling based on linear elastic behaviour of the materials made it possible to explain these variations by analysing the stress variations, particularly in the vertical direction. Viscoelastic modelling have shown that some additional stresses appear in the bituminous layer when the loads are moving away from the measurement point. These stresses are induced mainly by the reaction of the foundation layers (sub-base and sub-grade) and they are mainly caused by the interaction between the layers of the structures. Finally, the analysis of the strain and stress distributions near to the surface showed that bituminous materials are submitted to higher horizontal than vertical stresses just under the truck wheel. A particular and unexpected result of this situation is that the vertical strains at just under the wheel are tensile ones.