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.

随着道碴老化，道碴颗粒大小和形状的变化降低了排水能力，并导致铁路道碴更大的永久变形。因此，研究时效对不饱和镇流器力学行为的影响，并通过考虑时效效应来估计循环塑性变形具有重要意义。这里，“老化效应”是指细粒含量增加，颗粒形状与新鲜压载物相比变得圆润光滑。在本研究中，通过一系列循环加载三轴压缩试验，评估了老化对不饱和道砟循环塑性变形的影响。试验结果表明，道碴循环塑性变形受含水量、细粒含量和排水条件的影响较大，在完全不排水条件下，富水老化压载物的增加趋势更加显着，这是由于超孔隙水压力的产生导致有效围压下降。此外，两种类型的估计模型（即名为伊利诺伊大学厄巴纳-香槟分校 (UIUC) 模型的半经验模型和名为子加载表面扩展 (SSE) 模型的弹塑性模型）对预测的适用性本研究还通过与循环加载三轴压缩试验的结果进行比较，验证了不饱和道砟的循环塑性变形。结果表明，UIUC模型适用于预测完全排水条件下不同含水量的新鲜道砟（或轻度老化道砟）的循环塑性变形，通过考虑含水量和排水条件的影响，SSE 模型显示出估计新鲜和老化压载物循环塑性变形的良好潜力。本研究结果表明，排水条件对预测老化道碴循环塑性变形有显着影响，应根据水力特性（即渗透率）选择合适的三轴压缩试验（即 CD 和 CU 试验）试验条件。和保水性）老化压载物。