Estimating the Shakedown Limit for Granular Materials Under Cyclic Loading

The influence of cyclic loading on the deformation response of granular materials is usually described using the shakedown concept. The shakedown response can be characterized into different shakedown regions such as plastic shakedown, plastic creep and incremental collapse regions depending on the incremental plastic strains that occur in each loading cycle. Though different incremental strain limits are proposed in literature for different granular materials, the boundaries between these three stages in terms of stresses are still unclear. In this paper, the influence of loading conditions such as loading magnitude, frequency of loading, confining stress etc. and material compositions such as rubber content on the shakedown behavior of different granular mixtures is investigated. It is found that the normalized cyclic stress ratio which is a ratio of the cyclic stress amplitude to material's peak strength under static loading conditions can be used as a threshold value separating the plastic shakedown stage and plastic creep stages. By looking at laboratory data on two different granular materials, a unified criterion for estimating the shakedown limit under a wide range of loading and mixture properties is presented.