Development of the smear zone around vertical band drains

This study describes the effect of smear on the settlements of soft clay foundations which have been improved by installation of vertical drains. The smear zone propagation around a band-shaped drain was monitored using a large, radial drainage consolidometer. The test results reveal that a significant reduction in the horizontal permeability takes place towards the central drain, whereas the vertical permeability remains relatively unchanged. The estimated smear zone was about 3–4 times the cross-section area of the band-shaped drain (mandrel). In the analysis, the classical axisymmetric solution for consolidation by vertical drain has been converted into an equivalent 2D plane strain analysis. The plain strain model is subsequently applied to a number of embankments stabilized with vertical drains. It is revealed that the inclusion of smear effects improves the settlement prediction significantly.