Assessment of microfabric evolution in coral sand foundations reinforced by the vibroflotation compaction method

The microstructural evolution induced double-point vibroflotation in coral sand foundation soils is analyzed using industrial 3D micro X-ray computed tomography technology (μCT). Differences in densification efficacy are assessed by analyzing variations in the microfabric, including particle arrangement and pore structure. Two vertical positions and three planar positions are compared after double-point vibroflotation of two vibro-set groups. The results demonstrated that deeper layers exhibit a superior reinforcement effect compared to corresponding shallow layers, as evidenced by greater increases in the average coordination number (CN_ave) and more pronounced reductions in the average particle distance (APD). Among planar positions, both CN_ave and APD express that a great reinforcement effect arises at the vibro-compaction points. Meanwhile, the middle positions of the vibro-point set and the center positions of two vibro-point sets in the same plane present a similar effect. In addition, the calculated particle size distribution (PSD) curve consisted of intermediate principle axis matches best with that of the manual testing result through QICPIC. The PSD curve shows that finer particles migrates from deeper vibro-point position to surround. Overall, the larger excess pore pressure and overburden earth pressure attribute better densification effect at deeper layer. CN_ave relates to porosity ratio with a inversely proportional relationship because densification comes better particle contact and less porosity space. The microfabric evolution method is proved to be an effective on evaluating the characteristics of particle shapes, including elongation index (EI), flatness index (FI), and shape distribution pattern.