Three-dimensional hydro-mechanical analysis of geogrid-encased steel slag columns in soft foundations

Geosynthetic-encased stone columns effectively reinforce soft soils. This study develops and validates a three-dimensional coupled hydro-mechanical finite-element model to analyse steel slag columns encased by geogrids in saturated soft clay. Numerical outcomes match physical model tests, confirming the model’s capability to predict bearing capacity, column deformation, pore pressure dissipation and consolidation. Three modelling approaches – solid elements with apertures, solid elements without apertures and membrane elements – are compared. Results show that solid elements with apertures most accurately replicate drainage and consolidation. Increasing the infill’s friction angle also enhances lateral confinement and reduces column bulging, improving settlement response. Furthermore, higher geogrid stiffness significantly lowers both settlement and radial deformation, demonstrating an exponential improvement in foundation behaviour. A stiffness range of 2500–3750 kN/m is recommended. Overall, this study provides practical guidance for designing and modelling geogrid-encased steel slag columns in soft soil improvement.