Behavior of Floating Stone Columns in Soft Clay: Field Tests and Numerical Analysis

The use of floating stone columns (FSCs) has recently been adopted to improve the stability of thick soft clay deposits, though their behavior is not yet fully understood. To provide a comprehensive understanding, field load tests were conducted with varying area replacement ratios and length-to-diameter (L/D) ratios at Misono-cho, Suzuka City, Mie Prefecture, Japan. Bulging failure modes were observed using strain gauges, and stress sharing between the stone columns and the surrounding soil was monitored using earth pressure cells. The PLAXIS 3D (version 22) FEM program was used to conduct finite-element computations on 10-noded tetrahedral elements. The FEM model was calibrated and adjusted to account for the installation effects of FSCs and aligns closely with the outcomes of the field test. The settlement improvement factor for FSCs was found to be slightly higher in the long term compared with the short-term condition. Moreover, the settlement improvement factor increases with the applied stress and over time. The ultimate bearing capacity of FSCs depends on the additional confinement provided by adjacent columns. An improved model and design charts were proposed to estimate the ultimate bearing capacity and settlement of FSC-improved ground, showing lower relative error compared with other published results. Finally, a design procedure was anticipated to assist geotechnical engineers in designing FSCs constructed in soft clay.