A system of vertical drains combined with vacuum and surcharge preloading is an effective approach for promoting radial flow to accelerate soil consolidation. When a higher load is required to meet the desired rate of settlement and the cost of surcharge is also significant, the application of vacuum pressure with reduced surcharge loading can be used. The equivalent 2-D plane strain solution for multi-drain analysis is described with the inclusion of the effects of vacuum pressure and smear zone caused by mandrel driven vertical drains. A large-scale radial consolidometer is employed to determine the extent of the smear zone and the results are explained. The equivalent (transformed) permeability coefficients are incorporated in finite element codes, employing the modified Cam-clay theory. The 2D and 3D numerical multi-drain analysis is conducted to pre-dict the excess pore pressures, lateral and vertical displacements. Performance of two selected case histories are discussed and analysed, including the sites of Tianjin Port, China and Ska-Edeby embankment, Stock-holm, Sweden and the predictions are compared with the available field data. The study shows that, apart from realistic 3D numerical modelling, the equivalent plane strain solution can now be used as a predictive tool with an acceptable accuracy as a result of the significant process.
Indraratna, B, Rujikiatkamjorn, C and Ghandeharioon, A, Modelling of soft ground consolidation via combined surcharge and vacuum preloading, In Kartstunen, M & Leoni, M (eds), The 2nd International Workshop on Geotechnics of Soft Soils - Focus on Ground Improvement, 2008, 43-54, CRC Press: Taylor and Francis.