DEM Investigation of Geogrid Pullout Behavior in Open-Graded Aggregates

Abstract: Dense-graded aggregates are commonly used in pavement base and subbase layers because of their widespread availability and ease of compaction. However, the presence of fines in these materials often leads to moisture retention, which significantly lowers shear strength and increases the chance of shear failure or excessive permanent deformation. Frequent freeze–thaw cycles can further compromise their structural integrity, ultimately resulting in premature pavement distress. Open-graded aggregates (OGAs), characterized by superior drainage capacity and improved shear resistance, present a promising alternative. However, the stability of OGA layers is highly dependent on construction quality and the degree of compaction achieved. This study aims to investigate the performance of geogrid-stabilized OGA layers—an area with limited prior research— to assess how geogrid inclusion influences the mechanical behavior of OGAs. Given the limitations of traditional experimental testing in capturing micromechanical behavior, a particle-based, three-dimensional (3D) Discrete Element Method (DEM) framework was incorporated in this study to simulate and calibrate the response of geogrid-reinforced OGA assemblies under pullout loading conditions. Numerical pullout testing can provide valuable insights into the interaction mechanisms at the geogrid–aggregate interface. In this study, a triaxial geogrid of desired geometry was modeled in DEM using the Beamed Contact Model and calibrated through standard laboratory tests, while clumped-shaped particles were used to represent the ASTM #4 OGAs. A series of numerical pullout tests was conducted to evaluate the micromechanical response of geogrid-reinforced OGAs, with variations in porosity, applied surcharge, and geogrid tensile stiffness. The simulated pullout behavior demonstrated strong agreement with experimentally observed trends in pullout resistance. The DEM analyses enabled detailed visualization of displacement fields, contact force distributions within the OGA assembly, deformation patterns, and tensile force variations along the geogrid, hence offering valuable insights into the interlocking mechanisms between the geogrid and the OGAs.