Effect of the Smear Zone around SCP Improved Composite Samples Tested in the Laboratory

Abstract

In the design practice for sand compaction piles (SCPs), it is usually assumed that the state of in situ soil does not change during installation. In fact, there is evidence to suggest that extensive remolding of the preferred soil fabric can occur within the zone immediately surrounding the SCP during its installation. Properties of the soil within this heavily disturbed zone can effect pore pressure dissipation and hence the time after which the ultimate strength of the composite ground is available. In this study, the effect of the smear zone around SCPs is modeled using triaxial tests. SCPs of 25–80 mm diameter were installed in 100-mm-diameter cylindrical samples. The sand columns were installed by predrilling 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 undrained shear strength of the composite ground. Although both 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.