ABSTRACT
The Road authority specifications for unbound granular materials (UGMs) do not typically include a direct measure of resistance to rutting caused by repeated loading yet. These specifications can preclude the use of locally available aggregates or recycled materials that may provide adequate performance (resistance to rutting). As an alternative or compliment to current UGM assessment methods via specifications, a serviceability design method is proposed that utilises results from tests in the repeated load tri-axial (RLT) apparatus. Permanent strain behaviour at a range of stress conditions of four unbound granular materials (UGM) were assessed in the RLT apparatus. Behaviour was categorised into 3 possible ranges A, B or C, where A is a stable response and C is incremental collapse while B is intermediate. From this data, test stresses near or at the boundary of range A and B were determined to define a serviceability limit line stress boundary in p (mean normal stress)-q (principle stress difference) stress space. The serviceability limit line was applied as a yield criteria in a finite element model of a pavement to predict whether or not stable (Range A) behaviour occurs in the UGM for a range of asphalt cover thicknesses.
