Abstract
Subgrade compaction is a critical construction process for ensuring the structural stability and long-term service performance of highway engineering, and its quality directly affects the subgrade’s bearing capacity and deformation characteristics. However, traditional compaction quality evaluation methods primarily rely on post-construction sampling tests, which cannot capture the dynamic evolution of the subgrade structural state during vibratory compaction and provide limited guidance for optimizing vibration parameters and construction conditions. To address these limitations, this study conducted field-scale prototype vibratory compaction tests based on an actual engineering project, using a sandstone weathered soil–rock mixture as the filling material. The dynamic response characteristics of the subgrade under different vibration intensities and loose layer thicknesses were systematically analyzed. Acceleration time-history analysis, Fourier transform (FFT), Hilbert–Huang transform (HHT), and marginal spectrum energy analysis were employed to characterize the near-surface dynamic response and vibration-energy distribution of the compacted layer from the perspectives of the time and frequency domains and energy evolution. The results indicate that the subgrade’s vibratory response exhibits pronounced directional characteristics, with the Z-direction response being more representative of stability and energy concentration. For relatively large loose layer thicknesses, the strong vibration mode improves compaction effectiveness. In contrast, for a 30 cm loose layer thickness, efficient compaction can be achieved even under the weak vibration mode. The findings provide a reference for characterizing the dynamic response of highway subgrades under different vibratory compaction conditions and for selecting vibration parameters under similar field conditions.