Effect of Column Material Internal Angle of Friction and the Geotextile Stiffness on the Behavior of Group of Geosynthetic-Encased Stone Column

One of the most popular soil improvement methods is the use of stone columns to increase the bearing capacity and decrease settlements of buildings built on soft clay. Due to an absence of lateral confinement, the stone column treatment’s effectiveness is insufficient. The stone column’s bearing capacity is increased, and its amount of settlement is considerably reduced when it is encased with a geotextile. Numerical analyses were conducted to evaluate the effects of column material friction angle, geotextile stiffness, column diameter and spacing on the behavior of a group of encased stone columns (ESC) supporting a square isolated footing on soft clay. The analyses showed that increasing friction angle of the column material resulted in lower settlement reduction ratio (SRR) for ordinary stone columns (OSC), but had minimal impact on SRR for ESC. Increasing geotextile stiffness significantly decreased SRR for ESC, but the benefits diminished once stiffness exceeded 1000 kN/m. ESC also showed much higher stress concentration ratios compared to OSC, along with lower excess pore pressures. The mobilized hoop forces in the geotextile increased with applied stress but remained relatively constant for high column friction angles. The results demonstrate the effectiveness of geotextile encasement in improving the performance of stone column foundations, with the geotextile stiffness playing a more dominant role than the column friction angle. Parametric evaluation of column diameter and spacing demonstrated their significant influence on settlement reduction. The findings provide guidance on selection of appropriate geotextile properties for design of encased stone column ground improvements.