Semiempirical Cyclic Densification Model for Ballast Incorporating Particle Breakage

A number of constitutive models exist to model behavior of granular material under cyclic loading. Most of these models are useful to model soil behavior where the number of cycles is very small. Therefore, a semiempirical model is proposed to simulate the cyclic densification and degradation of coarse granular material under a railway environment where the number of loading cycles is very large. A kinematically expanding elastic surface is introduced to separate elastic and elastoplastic deformation of the material with the number of cycles. The reversible response is represented by the pressure-dependent elastoplastic rule. Empirical model parameters are introduced to consider the effect of stress history, stress ratio, number of cycles, and breakage. Model parameters are evaluated based on cyclic triaxial test results. Predicted results are compared with the laboratory data in order to demonstrate the model validity. The proposed model captures the realistic deformation and degradation of ballast at various frequencies and confining pressures for a large number of cycles.