Verification of rutting calculation for unbound road materials

Abstract

An analytical-mechanistic calculation method for the evaluation of rutting (permanent deformation) in unbound pavement layers and subgrade has been developed at the Technical Research Centre of Finland (VTT) over a period of years. The calculation method was generated from the test results of accelerated pavement tests along with complementary laboratory tests carried out in Finland. The test methods complemented each other and offered new possibilities for research. The stress distribution studies showed that it is very important to calculate stress responses in the pavement with an elasto-plastic material model to avoid tensile stresses in unbound materials, especially when the asphalt layers are thin. Thus, the new calculation method is based on the elasto-plastic stress responses and corresponding shear strength capacities. The shear strength approach was used because the rutting is supposed to be dominated by the shear strength ratio. The objective of this study was to verify the calculation method against two accelerated pavement tests: one from the Danish Road Directorate and the other from the Swedish National Road and Transport Research Institute. The verification indicated that the material model gave reliable results.