Assessment of smear parameters for use in wick drain design

Soft clay becomes remoulded around wick drains during their installation. The effects of remoulding can be taken into account in design by adopting an analytical method incorporating the radius of smear and the permeability of the remoulded soil in the smear zone. However, these parameters are usually not known and are estimated largely based on experience and guidance provided in the technical literature. Back analysis of settlement data from an embankment constructed on soft Pimlico Clay in Australia with a wick drain spacing of 1·5 m in an equilateral triangular configuration is performed to assess the potential smear parameters. A chart showing variations of permeability with smear radius is presented to assist with selection of design parameters for wick drains installed in soft Pimlico Clay. Effects of wick drain spacing on the permeability of the remoulded soil are investigated through back analysis of embankments constructed on wick drains spaced at 1·0 m and 1·35 m in an equilateral triangular configuration. Although the embankments are not constructed in identical ground conditions, there is no evidence that reducing the spacing between the wick drains causes the average permeability ratio to increase.