This study investigates the mechanical response and performance of biaxial polypropylene geogrid specimens cyclic loading. This work assesses the influence of embedment depths and subgrade strengths on the of geogrids. The experimental program involved subjecting the geogrid specimens to 100 repeated tensile loading cycles at four distinct load targets: 20%, 40%, 60%, and 80% of the geogrid ultimate tensile strength. The analysis focused evaluating the effects of preloading factors such as California Bearing Ratio (CBR) values, embedment depth, and the response to cyclic testing. Results show trends in stiffness reduction and changes in damping ratio with increased number of cycles. A comparative analysis was conducted with a control specimen from the same batch, highlighting the difference in mechanical response attributed to precycling variables. The findings indicate that the overall mechanical behavior of recovered geogrids is comparably consistent with new geogrids. However, variations in strain and stiffness reduction were observed among the recovered specimens, suggesting a pattern of yielding before failure. The findings suggest a minimal effect of embedment depth on the damping ratio at lower CBR. Overall, it was found that precycling and subgrade conditions have minimal effect on the mechanical response of the recovered specimens when tested in isolation.

This study presents an investigation into the mechanical behavior of geogrid-reinforced ballast subjected to cyclic loading focusing on the macro- and micromechanical features of the geogrid-ballast interaction mechanism. Key areas of interest include the effects of geogrid placement depth, aperture size, and stiffness on the motion of ballast particles, formation of contact force chains, and energy dissipation. A three-dimensional discrete element model, calibrated with experimental data, simulates ballast box tests performed on 300-mm-thick ballast layers reinforced by geogrids placed at depths ranging from 50 to 250 mm below the tie. The findings reveal that geogrids located within the upper 150 mm of the ballast layer significantly reduce tie settlement by minimizing particle movement, creating well-connected soil structures, and decreasing energy dissipation. Upon identifying 150 mm as the optimal geogrid placement depth, a parametric study evaluates the impact of the geogrid aperture size (A) and stiffness on the behavior of geogrid-reinforced ballast. The geogrid aperture size (A) is varied to give aperture size to ballast diameter (D) ratios ranging from 1.09 to 2.91, while the geogrid's stiffness ranges from 9.54 to 18.00 kN/m. Results indicate that A/D ratios greater than or equal to 1.45 are required for geogrids to perform satisfactorily, while stiffness appears to wield a negligible influence on the response of geogrid-reinforced ballast.