Abstract: The soil layers in the southwest of Iran are mostly soft and fine. Raft foundations undergo excessive settlement on these soils. In these cases, using piled raft foundations can decrease the settlements to some extent. But because of the low stiffness of soft clay, settlement is still more than expected. An appropriate solution is soil improvement. In this paper, a 3D nonlinear continuum FEM numerical model is adopted to investigate the possibility of increasing the efficiency of the pile-raft systems through top soft soil layer improvement. The improvement of the top soil layer is possible by, for example, backfilling on the soft ground surface, removing and replacing the top layer with compacted granular material, and mixing the top layer with cement or lime. The improved top layer thickness could be in the range of 1 through 4 m, in practical applications. The average settlement, maximum settlement, differential settlement, piled raft coefficient, and load distribution in a center pile for soft clay and improved clay are compared. It was observed that soil improvement caused settlement reduction significantly.