Formation mechanism of composite piers in clay-gravel mixture under punching and squeezing dynamic compaction
Year: 2026
Type: article
Abstract: Punching and Squeezing Dynamic Compaction (PSDC) is an important reinforcement method for forming composite piers in high-fill foundations. However, the relationships among hammer geometry, dynamic response, and internal three- phase structural evolution remain insufficiently understood. In this study, indoor PSDC model tests, direct shear tests, and CT scanning with 3D reconstruction were conducted under 18 test conditions by varying hammer angle, equivalent tamping energy level, and gravel content. The morphology, dynamic response, shear performance, and three-phase structural characteristics of composite piers were systematically investigated. The results showed that hammer geometry significantly affected both hole formation and composite pier morphology. The 60° hammer tended to form deeper and narrower holes as well as taller and narrower composite piers, whereas the 180° hammer tended to form shallower and wider holes, as well as shorter and wider composite piers. The dynamic response exhibited clear vertical dominance, horizontal attenuation, and staged accumulation. Compared with the 50% clay–gravel condition, the peak dynamic indices under the 60% clay–gravel condition reached 104.76–182.33% of those under the 50% condition, and the peak soil pressure reached 109.11–118.31% of that under the 50% condition. This indicates that a higher gravel content enhanced the overall transfer capacity of tamping energy within the composite piers. 3D reconstruction and structural statistics further showed that the 60% group was more likely to form a continuous gravel load-bearing skeleton, which corresponded to more pronounced shear strengthening. The relative increase in the friction coefficient was 3.35–6.45%, whereas the relative increase in cohesion was 2.44–4.32%. The findings indicate that the formation and strengthening of composite piers were jointly controlled by stress wave propagation, the development of the gravel skeleton, and the interfacial action of fine-grained soil particles. This study deepens the understanding of the formation and strengthening mechanisms of composite piers under PSDC, and provides a basis for optimizing relevant reinforcement parameters.
Source: SOILS AND FOUNDATIONS
Authors: Jianbin Xie, Yuchen Yang, Yinlei Sun, Rong-gu Jia, Ting Zhou, Yue Hu
Institution: Yunnan University
Language: English
Subfield: Civil and Structural Engineering
Field: Engineering
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $1,200
OpenAlex ID: W4412815549