A new material model for permanent deformations in pavements

Abstract

Today's demand in pavement design for a calculation method to evaluate rutting (permanent deformations) is wide and global. The new procurement methods together with functional requirements are underlining this rutting evaluation demand in different pavement materials and layers. Permanent deformation research has become more general during the last decade. VTT (the Technical Research Centre of Finland) has researched many different aspects of permanent deformations with accelerated pavement tests. Accelerated pavement tests have been conducted with the Heavy Vehicle Simulator (HVS-Nordic). The HVS tests have been completed with a wide triaxial test programme in laboratory. The HVS tests have shown that it is difficult to predict in advance where in the pavement rutting happens: in the subgrade or in the structural layers. A new material model based on the laboratory and HVS tests has been developed in VTT. The objective was to develop a material model for unbound materials, which is an analytical, nonlinear elasto-plastic model. The stress distribution studies of traffic load have shown that it was very important to calculate stresses in pavements with an elasto-plastic material model to avoid tensile stresses in unbound materials, especially when the asphalt layers were thin. The new material deformation model can take into account the number of the passes, the capacity
of the material and its stress state. The deformations in each layer are calculated and then summed together to obtain the total rutting on the surface of the structure.