ABSTRACT
One of the principal deterioration mechanisms for flexible pavements and ballasted railway track is the development of permanent surface deformation under repeated wheel loading. This can cause ruts in roads and differential settlement in railway track, both of which are major considerations in design and are caused by the accumulation of plastic strain under repeated loading. A review of these issues by Brown (1996 and 2004) described how observations from repeated load triaxial testing had demonstrated the existence of a threshold deviator stress level, below which the magnitude of accumulated plastic shear strain is quite small. The same phenomenon is apparent in the theoretical concept of shakedown, derived from structural engineering and first applied to pavements by Sharp and Booker (1984). The concept is that a material or structure will ‘shakedown’, after a certain number of load application cycles, into a state that responds in an entirely resilient, albeit non-linear, mode with no further accumulation of plastic strain. If this threshold or shakedown stress level can be reliably predicted or easily determined experimentally, then it provides a very useful component for design of pavement and railway track foundations.
