Investigation on the coarse-grained rearrangement of vibratory compaction in the high-speed railway graded aggregate materials

This paper aims to explore the coarse-grained rearrangement (CGR) phenomenon and its effect on the mechanical behaviors of high-speed railway graded aggregate (HRGA) materials during vibratory compaction. Firstly, the evolution of CGR is characterized by the analysis of mechanical behaviors and migration of the coarse grains in the HRGA materials. Then, a new indicator, the fraction of horizontally deflected coarse grains Hr, is proposed to evaluate the CGR, which increases with the rearrangement degree during vibratory compaction. Finally, using the discrete element method (DEM), the evolution of macro and micro mechanical properties of HRGA materials with different Hr-values (Hr = 0, 0.2, 0.4, 0.6, 0.8, and 1.0) are analyzed based on triaxial compression tests. The numerical results show that the shear strength of the assembly firstly increases with Hr and then reaches a plateau when Hr ≥ 0.6, which can be considered as the vibratory compaction steady state. For the microscopic behaviors, with Hr increasing, the enhanced interlocking between coarse particles makes it more difficult for them to rotate, leading to an increased proportion of sliding contact. Moreover, the effectiveness of the state of Hr = 0.6 was validated by the X-ray computed tomography (X-CT) scanning test. This research is expected to provide microscopic insights into the formation of internal structures for HRGA materials during vibratory compaction and provide a new method to assess the compaction quality of gravel fillers.