Coupled Mechanisms of Gravel Skeleton Structure and Directional Vibration Attenuation in Punching and Squeezing Dynamic Compaction: Insights from Physical Model Test and DEM Simulation

Jianbin Xie^1*Yuchen Yang^1*Rong-gu Jia^2*He Zhan¹Yue Hu¹Xuemin Zhang³

• ¹Yunnan University, Kunming, China
• ²Yunnan Construction Investment First Investigation and Design Co.,Ltd, Kunming, China
• ³Central South University, Changsha, China

Rapid growth of projects on high-fill sites under red clay and deep soft clayey foundations in Southwest China has exposed the limitations of conventional dynamic compaction in effective improvement depth and energy utilization. Punching and Squeezing Dynamic Compaction (PSDC) forms red clay–gravel composite piers through successive punching, backfilling and squeezing, offering potential advantages in deep densification; However, the mechanism of energy transmission and structural evolution remain unclear, constraining optimization of construction parameters and design. To address this gap, an integrated “Discrete element simulation–laboratory model testing–μCT 3D reconstruction” framework is established. Based on PFC3D with a Hertz contact model, impact-induced dynamic response and energy distribution were elucidated, and macro–meso consistency was verified against model tests and μCT-3D reconstructed piers, enabling systematic analysis of energy transfer, dissipation and skeleton reorganization under PSDC. Results show pronounced three-dimensional directional attenuation of impact energy: vertical transmission is the most efficient, the 45° oblique direction exhibits intermediate decay, and the horizontal direction attenuates rapidly with distance. Gravel content decisively governs energy pathways and skeletal architecture: a 60% gravel content produces continuous force chains, increases wave impedance, and concentrates energy at depth, promoting more effective compressive deformation and deep densification; in contrast, 50% gravel yields a more discrete skeleton, enhancing shallow random sliding, increasing sliding work, and promoting near-field dissipation. A directional attenuation model derived from a three-dimensional wavefront effectively fits the exponential decay of peak particle velocity with distance in the three directions and, for two representative gravel contents (50% and 60%), indicates a consistent chain linking gravel-skeleton connectivity, energy partitioning, and densification efficiency. These insights, obtained for 50%–60% gravel contents in high-fill red clay, illustrate how skeleton continuity regulates directional attenuation and densification, and they provide a basis for further extensions to broader mixture ratios and field scales.