Geotextile-encased cinder gravel columns: a coupled DEM–FDM analysis

Cinder gravel, a porous, lightweight, and durable volcanic byproduct, has the potential to be a sustainable and cost-effective alternative to conventional stone columns for ground improvement applications. Its use in soft soils, however, requires sufficient confining pressure to prevent bulging and thus performance degradation. Geotextile-encased cinder gravel (GECG) columns are an innovate method to overcome this, but studies on bearing response and pressure–deformation characteristics are limited. A comprehensive numerical analysis of GECG columns was conducted using a combination of the discrete-element method (DEM) and finite-difference method (FDM). The hybrid DEM–FDM framework enabled simulation of individual particle behavior while maintaining efficiency in modeling continuous, homogeneous materials. The key novelties were examining the macro and mesoscopic behavior of GECG columns under triaxial compression. The developed numerical model was validated and calibrated against triaxial test results. A parametric analysis of GECG columns investigated the influence of relative density and gradation on the compression behavior and load capacity. Upon triaxial compression, the results showed significant radial expansion near the column top, with stress and deformation fields aligning with the column's bearing capacity. The relative density had limited influence on the geotextile's radial deformation, while a higher content of coarse particles in the gradation enhanced the bearing capacity of the GECG columns.