Studying the Compaction Behavior of Open-Graded Aggregate Materials using Discrete Element Modeling

Abstract: Dense-graded aggregates in pavement base and subbase layers are susceptible to moisture fluctuations, which can significantly reduce their shear strength, leading to premature pavement failure. Open-graded aggregates (OGAs), with superior drainage qualities and improved shear strength, offer a viable alternative. However, traditional density-based compaction control methods are not applicable to OGA layers due to the presence of large void structures. In such a case, deflection-based compaction control procedures may offer a more appropriate and reliable approach that also correlates well with stability and performance of these layers. Currently, there is no standard compaction and construction guideline available for OGA materials. This paper will present findings from an ongoing research effort aimed at establishing deflection-based compaction control protocols for OGA layers utilizing the Light Weight Deflectometer (LWD). Extensive laboratory experiments were conducted to investigate how packing in OGA materials (meeting ASTM #4 gradation requirements) evolved with variation in compaction energies. Laboratory testing on the OGA materials was carried out at two different scales: (i) in a customized cylindrical mold (304.8 mm diameter x 292.1 mm height) with a vibratory shake table; and (ii) in a large wooden box (1220 mm x 1220 mm x 1220 mm) with a vibratory plate compactor. LWD tests were carried out to record the surface deflections on top of the aggregate layers after different stages of compaction. A commercially available Discrete Element Modeling (DEM) software, Particle Flow Code (PFC) was employed to simulate these laboratory tests to gain in-depth understanding of aggregate packing behavior. The developed model was calibrated using laboratory test results. LWD-measured surface deflections were found to have a strong correlation with the compaction energy applied to the OGA materials. A parametric study was undertaken to evaluate how various model parameters influence the packing nature and LWD-measured surface deflections. The DEM analysis further explored the effect of vibration frequency, vibration amplitude, compactor weight, compaction duration on the degree of packing of OGA matrix.