The use of vertical drains with vacuum preloading is considered as the most effective and economical method for improving soft clays (normally consolidated to lightly over-consolidated) to eliminate settlements of the permanent infrastructure. Application of vacuum pressure via prefabricated vertical drains promotes radial flow consolidation enhancing the shear strength of the compressed ground. In this paper, the mechanisms of the vacuum preloading system based on current practices are described through the selection of the important design parameters. The equivalent plane strain solution for both Darcian and non-Dracian flow are presented to predict the excess pore pressures, lateral and vertical displacements. The numerical analyses incorporating equivalent plane strain solutions were performed to predict the soil responses based on two selected case histories in Thailand, one with vacuum and the other without vacuum application. The research findings provided insight as to which of the above aspects needed to be simulated accurately in numerical modelling. It is found that the accuracy of modelling depends on the correct selection of the constitutive model applied in the numerical analysis. Finally, a parametric study of the combination of vacuum and surcharge preloading was conducted to demonstrate how any excessive lateral displacements can be avoided.