Influence of Footing Geometry on the Behavior of Floating Stone Columns in Soft Clay

Abstract

Stone columns are commonly used to improve the bearing capacity and reduce the settlement of soft cohesive soils; however, the effects of footing shape and area replacement ratio on the floating stone column (FSC)–improved ground remain unclear. Short-term field load tests were conducted at Misono-cho, Suzuka City, Mie Prefecture, Japan, for footings with area ratios varying from 0.14 to 0.56 and footing length-to-width ratios up to 4. A three-dimensional finite-element model (FEM) was calibrated and validated against field measurements, showing good agreement with observed stress–settlement responses. The results indicate that increasing the area replacement ratio substantially improves the bearing capacity. Increasing the footing length-to-width ratio reduces the bearing capacity up to 7% at lower area ratios, while the reduction was limited to 3% at higher area ratios. The shear strain response obtained from the FEM analysis indicated a transition from punching-dominated behavior to bulging-dominated failure at a critical L / D of 6.67. Square footings produced a triangular failure zone with a larger influence depth, while rectangular footings caused a trapezoidal zone with a smaller, nearly uniform influence depth, resulting in reduced bearing capacity. Using the equivalent homogeneous composite ground approach, bearing capacity and shape factor equations were developed and compared with published studies for validation. The findings highlight the significant influence of footing geometry on the stress distribution, influence depth, and failure mechanism of FSC-improved ground.