Verification of Box Test Model and Calibration of Finite Element Model Evaluation of Railroad Ballast Performance

The development of innovative models to evaluate railroad ballast performance can reduce railroad maintenance costs and improve train operation and safety. A significant portion of the maintenance costs associated with track transportation systems can be attributed to ballast degradation (fouling). Understanding the mechanisms and the effects of ballast fouling is becoming increasingly important with the increased demand on track transportation systems and as trains become faster and carry more weight. This paper presents the results and findings of a finite element (FE) model to evaluate and validate a railroad ballast box test apparatus developed at the University of Massachusetts, Amherst. FE modeling of the box test was conducted to provide insight for subsequent laboratory box test experiments. Boundary and scale effects of the box test were evaluated through the FE model, and the stress-strain behavior and distribution were explored. The predicted relationship between the elastic modulus and the percentage of fouling of the ballast by wet clay was found through calibration of the FE model. The FE model showed that the boundary conditions of the box governed the behavior of the model, specifically, that the addition of smooth and flexible walls reduced strength capacity and increased plastic deformation of the ballast. The FE model also showed that by increasing the size of the box by approximately 50%, stress concentrations below the tie, which would have led to a failure mechanism resembling punching shear, were avoided.