The Characteristics of PVD Smear Zone

A smear zone, i.e., a disturbed zone is considered to form during installation of a prefabricated vertical drain (PVD) using a mandrel and this zone retards the horizontal consolidation of soft clays in the vicinity of PVD. The characteristics of the smear zone, such as its extent and hydraulic conductivity remain discrepant among investigators. This study attempts to determine the extent of the smear zone and to measure the hydraulic conductivity of the smear zone directly by laboratory tests. For this purpose, a Smear Zone Model (SZM) test is described. The tests indicate that two soil zones are identifiable in the soil mass surrounding the PVD after the PVD installation using the mandrel. The extent of the smear zone is about 3 to 4 times the equivalent radius of the mandrel depending on soil type. The smear zone permeability ratio was measured to be about 1.03 to 1.25 for the soils tested. However, the test conditions employed were least conducive to generating a highly disturbed zone.