Influence of column spacing on geosynthetic-encased columns behavior in very soft clay

This study evaluates the influence of column spacing on the mechanical behavior of geosynthetic-encased columns (GECs) installed in very soft clay under vertical surcharge loading. A large-scale physical model (1.6 m × 1.6 m × 1.2 m) was instrumented with settlement gauges, piezometers, and pressure cells to monitor performance. Column spacing varied between 2.0D and 3.5D (D = column diameter) to assess effects on settlement, excess pore pressure, stress distribution, and the lateral earth pressure coefficient (K). Smaller spacings led to reduced settlements, faster pore pressure dissipation, and more efficient stress transfer to the columns. In contrast, larger spacings resulted in higher excess pore pressures and reduced system effectiveness. The coefficient K varied with spacing and depth: higher K values were associated with smaller spacings and shallower depths due to increased lateral confinement and interaction among columns. Conversely, deeper measurements showed lower K values due to limited lateral deformation. Comparison between measured and predicted settlements and encasement forces demonstrated good agreement, validating existing analytical models. The findings highlight the critical role of column spacing in optimizing the performance of GEC-reinforced soft soils under surcharge loading.