Dynamic behaviors of fine-grained subgrade soil under single-stage and multi-stage intermittent cyclic loading: Permanent deformation and its prediction model

The realistic simulation of the train dynamic loading is essential to the study of the dynamic behaviors and longterm stability of the railway subgrade. Considering the loading intermittence caused by the time interval between adjacent trains and the increasing dynamic stress response of the subgrade caused by the increasing axle load and running speed of trains, a series of dynamic triaxial tests with single-stage and multi-stage intermittent cyclic loading were performed. The results show that the existence of the intermittent stage improved the resistance of samples to cyclic loading and thus reduced the permanent strain, and the initial small dynamic stress under multi-stage loading also effectively reduced the accumulation of permanent deformation under the subsequent large dynamic stress. Based on the time-hardening approach, a prediction model for the permanent strain was proposed to consider the influence of loading intermittence and multi-level dynamic stress, and this model can predict the permanent strain under single-stage and multi-stage intermittent cyclic loading well. The research results can provide guidance for further understanding of the deformation characteristics and settlement prediction of railway subgrade under actual train loading.