A system of prefabricated vertical drains (PVDs) with a surcharge load is an effective method for accelerating soil consolidation by promoting radial flow. This study presents a three-dimensional (3D) finite element model for soft soil improved by a single drain. In the finite element analysis, the actual rectangular PVD cross-section is considered, and the equivalent drain diameter is then back calculated based on the consolidation curves. The numerical predictions are then compared to previous studies. The settlements observed in the laboratory are subsequently compared with the three-dimensional finite element analysis incorporating the modified Cam-Clay model and Hansbo’s theory.