Behaviour of clay reinforced by sand compaction pile with smear

In the design practice for sand compaction piles (SCPs), it is usually assumed that the state of in situ soil does not change during the installation. In fact, there is evidence to suggest that extensive remoulding of the preferred soil fabric occurs within the zone immediately surrounding the SCP. Properties of the soil within this heavily disturbed zone can affect the pore pressure dissipation, and hence the time after which the ultimate strength of the composite ground would be available. In this study, the effect of smear zone around SCPs is modelled in the laboratory using triaxial tests. SCPs of 25–80 mm diameter were installed in 100 mm diameter cylindrical samples. The sand columns were installed by pre-drilling a hole and then backfilling it with well-compacted sand. The smear zone was created by using a rough casing to drill the hole. The effect of the smear zone on SCP was investigated by observing the change in pore pressure during consolidation and the undrained shear strength of the composite sample. Although the shear-induced pore pressures and the undrained shear strength of the composite samples could reasonable be predicted, wide scatter still existed in the relationship between the stress concentration factor and the area replacement ratio.