Shakedown of unbound granular material

Compacted unbound granular materials are extensively used as sub-layer in pavement design. Most pavement design guides assume that they are responsible for the degradation and deformation of the roads and railways that they support. Biaxial tests are usually employed to investigate the elasto-plastic response of these materials to cyclic loading. A particularly interesting question is whether a limit load exists, below which the excita-tions shake down, in the sense that the material does not accumulate further deformations. We have carried out a detailed study of the elasto-plastic behavior of a simple model of unbound granular matter submitted to cyclic loading. The dissipated energy through out the simulation has been used for the characterization of the different regimes of responses. 1 Introduction. Traditional pavement design methods are still almost completely empirical. Long term experience with the performance of on-service roads is supplemented with the results obtained from especially constructed test pavements. Changes in material properties, the loading or the environmental conditions can be hardly investigated. The information obtained from the experiments is therefore limited. The disadvantages of traditional design have become more obvious during the last decades as a consequence of the growth of transportation needs and the urge for using recycled materials. Mechanistic and analytical design procedures have consequently been developed based on the analysis of the response of the structure under specific loads. Understanding the behavior of the components of the structure is of course a prerequisite of this approach.