Numerical Evaluation of the Behavior of Ballast-TDA Mixture in the Box Test Using Discrete Element Method

Ballast materials play a very important role in rail tracks, the most important of which is the distribution of stresses to the bottom layers and the provision of proper elasticity and drainage. At the same time, one of the main problems of these materials is particles breakage due to dynamic transit loads as well as tamping operations, which over time, especially for weaker rocks, lead to high fouling and the need for frequent maintenance and repair. One of the proven solutions to increase the service life of ballast materials and reduce the maintenance problems caused by it, is to add an optimal percentage of TDA to the ballast, which helps to improve the abrasion behavior and durability of the material and causes less particles breakage. In this paper, the behavior of ballast materials mixed with TDA is numerically investigated using two-dimensional simulation of ballast box test with discrete element approach. Using this numerical modeling in PFC software, which has been validated by actual laboratory study of ballast box test, the effects of increasing axial load (different stress levels) and operating speed (different loading frequencies) are evaluated by performing a parametric study within the optimal percentage range. Based on this, the optimal mixing percentage between ballast and TDA materials in different stress and frequency conditions has been determined. The results showed that the stress level has a very high effect on the results, while the effect of frequency is much lower. According to the results, also 5 to a maximum of 10% by weight of TDA can be proposed as the optimal mixing percentage both in terms of settlement and particles breakage.