Numerical simulations based on 1D or 2D methods are insufficient to integrally describe the consolidation behaviors of sand drained foundations. On the other hand

it is very difficult to simulate the coupled three-dimensional consolidation in the situation that sand drains are dense. However

plane deformation and spatial seepage (PDSS) analysis is sufficient and acceptable. On the basis of symmetry principle and Biot’s consolidation theory

the PDSS modeling proposed is improved. A more reasonable scheme of 3D FEM grid is developed for sand drained ground in which drains are distributed on the pattern of equilateral triangle. Drains are located on nodes instead of elements and the special characteristics of radial drainage are considered. The improved model also is connected to an inverse method and applied to an engineering project to analyze the subsidence of a soft foundation preloaded by combined vacuum and embankment as well as the flux of water discharged by sand drains