The installation of drains creates a disturbed region known as a smear zone where the change in the clay structure affects the horizontal permeability and compressibility. The parameters required to characterise the smear effect are the extent of the smear zone and the ratio of the horizontal coefficient of permeability in the undisturbed zone and in the smear zone. Only limited studies have been carried out on different aspects of soil disturbance due to driving vertical drains and its effects on the subsequent consolidation. In this paper the disturbed zone around a rectangular mandrel was characterised using soil samples obtained from the soft clay layer at various locations beneath an embankment built at Ballina, Australia, where vertical drains were installed. By determining the change in the coefficient of permeability, the water content and volume compressibility across the smear zone, the effects of soil disturbance on consolidation due to the installation of drains can be quantified using the available numerical model.