Detection of smear zone using micro-cone and electrical resistance probe

The installation of a prefabricated vertical drain (PVD) using a mandrel results in soil disturbance adjacent to the PVD, which is known as the smear zone. The smear zone is investigated by a series of radial penetration tests including a micro-cone penetrometer and an electrical resistance probe in the clay specimen prepared in a large-scale chamber. The 5 mm diameter micro-cone penetrometer and the 2.1 mm diameter electrical resistance probe produce continuous soil strength and electrical resistivity profiles around the PVD. Almost-constant values of the cone tip resistance and electrical resistivity are measured within the undisturbed zone. The outer boundary of the smear zone is clearly defined by the locations where the deviations of the measured cone tip resistance and electrical resistivity from the constant values are observed. Significant changes in both measurements are observed in the smear zone with remarkably consistent patterns. The smear zone induced by the PVD installation using a rectangular mandrel has an elliptical shape and extends to approximately 3.2̃3.4 times the half-length of the mandrel and 5.3̃5.4 times the half-width of the mandrel.