Shakedown response of recycled rubber–granular waste mixtures under cyclic loading

Understanding and quantifying the long-term deformation behaviour of granular materials under repeated loads is imperative for ensuring the longevity of railway tracks. One of the most relevant characteristics of granular materials under repeated cycles of loading and unloading is their ability to achieve a relatively stable state (shakedown) after being subjected to initial compression. The shakedown response of blended rubber–granular waste mixtures under triaxial test conditions has been investigated in past studies highlighting the influence of the rubber content, confining stress and cyclic loading amplitude. However, a clear methodology for estimating shakedown yield limits of these granular mixtures has not been discussed in detail. The current study highlights the influence of the peak shear strength of these mixtures under static loading on their shakedown response in cyclic loading conditions. It is observed that the variation of static shear strength with rubber contents and confining stresses is found to affect the shakedown response. A unified method of estimating the shakedown limit is proposed by analysing permanent axial strains with normalised cyclic stress ratio at different loading cycles. The proposed method is validated through two independent sets of drained cyclic triaxial test data on coal wash–rubber crumb mixtures and rail ballast.