This paper describes recent research the aim of which was to develop permanent deformation design transfer functions for unbound pavement layers from Heavy Vehicle Simulator (HVS) test data. Two types of data generated during an HVS test are used to develop the permanent deformation models on which the design transfer functions are based. These are the in-depth deflection and permanent deformation data obtained from the Multi-Depth Deflectometer (MDD) measurements taken at regular intervals during an HVS test. Test data from a number of HVS tests, selected from the moderate and wet regions in South Africa, were used for the development of the permanent deformation models.

A multi-dimensional, conceptual model for permanent deformation was developed and calibrated with HVS test data for pavement foundation and structural layers of different material qualities. These models provide permanent deformation design transfer functions at different expected performance reliabilities for unbound pavement layers in South Africa.

The use of these design transfer functions is illustrated by a number of examples. The design approach allows each of the pavement structural layers and the pavement foundation to contribute to the total deformation or surface rut of the pavement structure.