In this study the characteristics and extent of the smear zone are investigated using a large, undisturbed sample. The aim of using such a sample is to capture the realistic characteristics of the smear zone in relation to the in situ soil structure during the installation of prefabricated vertical drains (PVDs) using a mandrel. The extent of the smear zone for Bulli clay (New South Wales, Australia) is determined on the basis of normalised permeability (k(h)/k(hu)) and the reduction in the water content upon consolidation. The permeability and compressibility of the soil are investigated to determine the extent to which the soil surrounding the PVD has become disturbed. In laboratory testing, the soil consolidation behaviour due to a PVD is studied using a large-scale consolidometer apparatus. The numerical results have shown that the writers' solutions give excellent agreement with laboratory observations.