Ground improvement of soft soil by geotextile-encased columns

This paper compares the field response of two test embankments constructed on similar soft soil deposits. The un-strengthened foundation had vertical drains underneath the embankment and the strengthened foundation had geotextile-encased granular columns, both provided with basal geogrid reinforcement. The effectiveness of the encased granular columns was assessed by comparing the settlement below the embankments, the horizontal displacement of the soft foundation and the excess pore pressures in the middle of the soft clay layer. The results showed that the granular encased columns significantly reduced the maximum settlement occurring below the embankment as well as the maximum horizontal displacement in the clayey foundation. At the same settlement level, the load-carrying capacity of the strengthened foundation was found to increase by as much as around 2·5 times that of the un-strengthened one. It was also observed that the geotextile-encased granular columns caused a noticeable reduction in the maximum excess pore pressure following load application. Furthermore, the degree of consolidation achieved at the end of embankment construction was quite high when encased granular columns were used.