Field study on compaction effect and energy evolution characteristics of highway subgrade under low-amplitude vibration

Subgrade compaction is a critical procedure in highway construction. To elucidate the dynamic characteristics and energy transfer mechanisms throughout the entire compaction process, this study utilized four test lanes to conduct field experiments on highway subgrade under varying numbers of rolling passes. Comprehensive measurements and analyses were performed regarding the dynamic characteristics of vibration waves, energy distribution, and the evolution of soil compactness during operation. Furthermore, the compaction efficiency and energy transfer within the subgrade were quantitatively evaluated. The results indicate that the dynamic behavior of subgrade materials varies significantly across different compaction stages, which are consequently categorized into three distinct phases: loose, optimal compaction, and over-compaction. In this experiment, the third rolling pass represented the optimal compaction state, characterized by distinct resonance peaks, a regular frequency spectrum, and highly efficient energy transfer. As compactness increases, the horizontal propagation of vibration waves strengthens, whereas vertical attenuation accelerates, causing energy to concentrate beneath the vibration source. Additionally, the proposed method for evaluating compaction efficiency based on the energy transfer coefficient corroborates the three-stage evolution of the process, offering a direct, quantitative indicator for real-time quality assessment and endpoint determination. These findings provide new theoretical insights and empirical data to support intelligent and refined process control in subgrade compaction.