Long-term geomechanical behavior of geogrid-reinforced ballast in dynamic triaxial tests

During operation, the ballast is subjected to a gradual breakage process that causes clogging of the substructure. Intervention periods on the ballast layer generate high costs that impact the long-term competitiveness of railways. In this context, this work aims to evaluate the geomechanical behavior of reinforced ballast, assessing the effect of reinforcement and stiffness provided by the addition of geogrids. Using 3D printing, the two reinforcement elements were manufactured with PETG and PLA polymers to represent the commercial geogrids Basetrac Grid PET40 and PET65, respectively. Long-term cyclic triaxial tests were used to evaluate the geomechanical behavior of the ballast. The results show that the PLA polymer was more efficient in reducing the deformability of the ballast. Long-term tests also demonstrated that granular materials tend to stabilize plastic deformations, which were not achieved under the stress level and loading frequency adopted in this research, even with the inclusion of geogrids. The low degree of grain breakage shows that the use of cubic particles, together with a well-graded distribution, helps to reduce aggregate degradation in the ballast layer. However, the high confinement levels used in the triaxial tests may have reduced the effect achieved by the reinforcement element. Factors associated with the model geogrids, such as high stiffness, low flexibility, and reduced aperture, also influenced the interaction with the aggregates.