Dynamic behaviours of railway's base course materials subjected to long-term low-level cyclic loading: experimental study and empirical model

The aim of this research was to develop a practical method for estimating the dynamic elastic modulus and accumulated plastic strain of a railway's base course materials subjected to increasing long-term, low-level cyclic loading. For this purpose, two series of cyclic triaxial tests, one with single-stage and the other with multi-stage loading, were performed. It was found that the accumulated plastic strain increased as the number of cycles and amplitude of the loading increased, but that the permanent strain decreased as the confining pressure became higher, and appeared to be closely related to the stress history. Considering the effect of the stress state, an empirical model was proposed to predict the accumulated plastic strain. Then, the model was modified on the basis of the time-hardening approach. In this way, permanent deformations in various stress stages were accumulated using an equivalent number of load cycles. There was good agreement between the predicted and measured deformation.