With the ballast aging, the changes in the size and shape of the ballast particle reduce the drainage capacity, as well as cause a greater permanent deformation of the railroad ballast. Therefore, it is meaningful to investigate the effect of aging on the mechanical behavior of unsaturated ballast, and to estimate the cyclic plastic deformation by considering the aging effects. Here, “aging effect” means the increase in fine fraction content and the particle shape becomes rounded and smooth as compared with fresh ballast. In this study, the influence of aging on the cyclic plastic deformation of unsaturated ballast was evaluated through a series of cyclic loading triaxial compression tests. Test results indicate that the cyclic plastic deformation of ballast is seriously affected by water content, fine fraction content and drainage condition, and the increasing trend becomes more remarkable at the water-rich aged ballast under the fully undrained condition since the effective confining pressure decreases due to the generation of excess pore water pressure. Furthermore, the applicability of two types of estimation models (i.e., a semi-empirical model named University of Illinois at Urbana-Champaign (UIUC) model, and an elasto-plastic model named subloading surface extension (SSE) model) to the prediction for cyclic plastic deformation of unsaturated ballast is also verified in this study by comparing with results of cyclic loading triaxial compression tests. As the result, it is revealed that the UIUC model is suitable for predicting the cyclic plastic deformation of fresh ballast (or slightly aged ballast) with different water contents under the fully drained condition, and the SSE model shows good potential to estimate the cyclic plastic deformation of fresh and aged ballasts by considering the effects of water content and drainage condition. The findings of this study indicate that drainage conditions have a significant effect on predicting the cyclic plastic deformation of aged ballast, and appropriate test conditions for triaxial compression tests (i.e., CD and CU tests) should be selected according to hydraulic properties (i.e., permeability and water retentivity) of the aged ballast.
All Science Journal Classification (ASJC) codes
- Civil and Structural Engineering
- Geotechnical Engineering and Engineering Geology