Numerical modelling of vacuum preloading & field applications
This study describes the effect of unsaturation at a drain boundary on the behaviour of a single prefabricated vertical drain subjected to vacuum preloading based on a two-dimensional plane strain finite element model incorporating the modified Cam Clay model. Unsaturation of soil adjacent to the drain can occur due to mandrel withdrawal or application of vacuum pressure through prefabricated vertical band drains (PVDs). Following initial laboratory simulation in a large-scale radial drainage consolidometer, the authors have attempted to explain the observed retardation of pore pressure dissipation through a series of models, which consider the effect of unsaturation at the drain-soil interface. The results indicate that the introduction of an unsaturated soil layer adjacent to a PVD improves the accuracy of numerical predictions. Lastly, a multidrain analysis is conducted to study the behaviour of an embankment stabilized with vertical drains subjected to vacuum preloading, and the field measurements are compared with a series of numerical model predictions.Key words: consolidation, embankment, finite element method, settlement, soft clay, vacuum preloading, vertical drains.