Performance analysis of geotextile-encased stone columns using a simplified analytical approach.

Geosynthetic-encased stone columns (GESCs) effectively improve soft soils where traditional stone columns lack sufficient lateral confinement. The complex interaction among the column, encasement, and surrounding soil necessitates an analytical model for efficient prediction and design. This study presents a simplified semi-analytical iterative solution to evaluate ground reinforced with GESCs. The system is modeled as a unit cell with regularly arranged end-bearing stone columns in soft soil. The stone column is idealized as a rigid-plastic material, yielding at active stress and deforming plastically without volume change, while the geosynthetic encasement is represented as linear-elastic, and the surrounding soil is modeled using semi-empirical assumptions in which horizontal stresses are linearly proportional to vertical stresses. The soil profile is divided into horizontal slices to account for depth-dependent behavior, applicable to both homogeneous and layered soils, and to un-encased, partially encased, or fully encased columns. Validation with field tests and finite element analysis shows that the proposed solution provides comparable results for settlements, stress distribution in both soil and stone columns, and encasement radial expansion. The model is effective across a wide range of area replacement ratios (i.e., 0 to 0.35) and encasement stiffnesses (0 to 5000 kN/m), with optimal stiffness effects calculated between 2000 and 3000 kN/m. Parametric analyses reveal that settlement improvement and stress concentration are most sensitive to the area replacement ratio, encasement stiffness, and soil stiffness, while increasing column diameter beyond an optimal value reduces effectiveness. An optimum partial encasement length ratio of 0.45 was identified, beyond which the Settlement improvement factor (SIF) increases only marginally. The proposed model also provides an analytical design chart for evaluating the settlement of GESC-reinforced soft soils, along with a Python-based code for calculation.