Cumulative permanent strain and critical dynamic stress of silty filler for subgrade subjected to intermittent cyclic loading of trains.

The long-term loading of the trains on the subgrade in service is the cyclic loading when the train passes and the intermittent stage when there is no train passing. However, in most studies, continuous loading was used to investigate the dynamic characteristics of a subgrade soil, which ignores the effect of loading intermittence. The aims of this research were first to study the cumulative permanent deformation behaviors under intermittent cyclic loading of trains, then to establish the classification criterion for cumulative permanent strain behaviors, and finally to propose a practical method for estimating the critical dynamic stress in the intermittent loading mode. For this purpose, according to the actual conditions of the subgrade of Shuo-Huang Heavy-Haul Railway, the monotonic triaxial test and the cyclic triaxial test with intermittent loading were performed. Based on the shakedown theory, the cumulative permanent strain behaviors under intermittent loading can be classified into three categories of plastic shakedown, plastic creep, and incremental collapse. Then, the classification criterion was established based on the permanent strain rate. Finally, an empirical formula of critical dynamic stress for intermittent loading, which could also consider the varying moisture content, was proposed. [ABSTRACT FROM AUTHOR]