Modelling of combined vacuum and surcharge preloading with vertical drains

In this study, 2D and 3D numerical analyses were conducted to predict embankment behaviour on soft clay foundations stabilised by Combined Vacuum and Surcharge Preloading. To determine the equivalent plane strain permeability, a revised conversion procedure for plane strain condition considering linear permeability variation in the smear zone is proposed. The equivalent permeability coefficients are then incorporated in finite element codes, employing the modified Cam-clay theory. The advantages and limitations of vacuum application through vertical drains are discussed through two selected case histories from China and Australia and the predictions are compared with the available field data. Apart from realistic 3D numerical modelling, it is demonstrated that the equivalent plane strain analysis can now be used as a predictive tool with acceptable accuracy.