A full-scale test embankment was constructed on a soft deposit (S-u < 20 kPa) improved by geotextile-encased granular columns to assess its serviceability performance for a nearby stockyard foundation. The behaviour of the improved foundation was monitored by means of instrumentation with respect to surface settlements, excess pore pressures, total vertical stresses acting on the top of the encased column and surrounding soft soil as well as geotextile radial deformation. Two-dimensional finite-element analysis was performed using an axi-symmetric unit cell, and then the results were compared with field measurements. It was observed that the soil arching progressed during post-construction due to a decrease in apparent stiffness of soft clay from quasi undrained to drained stiffness. Furthermore, there was a difference in settlement between the top of the encased column and the surrounding soft soil, midpoint between the columns, which increased during both construction and consolidation stages. A measured relation was also found to correlate the geotextile expansion with the maximum settlement occurring below the embankment.